University of Ghana http://ugspace.ug.edu.gh THE INFLUENCE OF RICE HUSK BIOCHAR AND NITROGEN SOURCES ON THE GROWTH OF LOWLAND RICE ON AN EUTRIC GLEYSOL FROM WALEWALE BY GIBRILLA AHMED (10088285) A THESIS SUBMITTED TO THE UNIVERSITY OF GHANA IN PARTIAL FULFILMENT OF THE REQUIREMENT FOR M.PHIL SOIL SCIENCE Department of Soil Science School of Agriculture University of Ghana Legon, Accra, Ghana. July 2018 University of Ghana http://ugspace.ug.edu.gh DECLARATION I hereby declare that the thesis herein presented for the award of Master of Philosophy in Soil Science is a result of my investigation. All references to other authors’ work as sources of information are duly acknowledged. ……………………………. ……………………….. GIBRILLA AHMED Date (STUDENT) …………………………. ……………………….. Dr. Mrs. STELLA ASUMING - BREMPONG Date (PRINCIPAL SUPERVISOR) ……………………………. ……………………….. Dr. ERIC K. NARTEY Date (CO-SUPERVISOR) i University of Ghana http://ugspace.ug.edu.gh DEDICATION This work is dedicated to my dear wife Asana Salifu, the memory of my late parents Abdulai Gibrilla and Fatima Addy. Without their endless support and encouragement, thoughtful guidance and genuine care, I would not have achieved all I have achieved. ii University of Ghana http://ugspace.ug.edu.gh ACKNOWLEDGEMENTS My utmost gratitude goes to The Almighty Allah for the gift of life to complete the study successfully, but for you, I would not have made it this far. My sincere gratitude and deep appreciation goes to my supervisor, Dr. Mrs. Stella Asuming- Brempong for her guidance, support in helping me realize my potential. I am extremely grateful for the extent you went to make sure my work was done and completed on time. Allah richly bless you. I wholeheartedly extend my thanks to Dr. Eric K. Nartey, my co-suprvisor for his critique and keeping me on track throughout my research work programme. To all the Lecturers of the Department, I say a very big thank you and ask for Allah’s blessings for your support, suggestions, encouragement and love they showed me throughout my two-year study. My acknowledgement will not be complete without expressing my profound gratitude to West Africa Agricultural Productivity Programme (WAAPP) and USAID-Ghana/University of Ghana Institutional Capacity Building for Agricultural Productivity Project for their financial support towards my academic work. Finally, my special thanks go to all my friends and Laboratory technicians of the Soil Science Department for their support during Laboratory analysis of my samples. iii University of Ghana http://ugspace.ug.edu.gh ABSTRACT Soil nutrient depletion in lowland rice growing ecologies in Northern Ghana is one of the major causes of low rice yields. Most nutrients applied to enhance the fertility of soil are lost through leaching due to the low CEC of the soils caused mainly by low organic matter and low colloidal clay content of the soils. The application of biochar has been found to improve soil fertility through its enhanced nutrient retention leading to increased nutrient uptake and consequently increased crop yield. The study therefore focused on assessing the potential of using rice husk biochar in combination with different sources and levels of nitrogen on productivity of a soil from lowland rice ecology. The hypothesis was that rice husk biochar in combination with inorganic or organic N will improve the growth and yield of rice and chemical properties of a typic Eutric Gleysol. Soil samples used for the study were collected from a lowland rice growing field in Walewale and some physical and chemical properties of the soil were determined before applying the soil amendments. A pot experiment involving twelve treatments were laid out in a complete randomized design with three replications. Two biochar application rates of 0 t/ha and 50 t/ha were combined factorially with three different rates of nitrogen at 0 kg/ha, 50 kg/ha and 100 kg/ha from two different sources viz, sulfate of ammonia and cowdung. Growth parameters such as weekly plant height and weekly tiller number were monitored one week after transplanting to harvesting. After harvest, the grain yield, straw yield and plant nutrient concentrations were determined. Residual soil analysis was carried out after harvest. The results of the study showed that grain and dry matter yield, N uptake and residual soil total N and C were influenced by amendment with biochar at 50 tons/ha. The combination of biochar at 50 tons per ha with inorganic nitrogen at 100 kg/ha produced the highest grain yield/pot and the highest nitrogen use efficiency (NUE). iv University of Ghana http://ugspace.ug.edu.gh TABLE OF CONTENTS TITLE PAGE DECLARATION ............................................................................................................................. i DEDICATION ................................................................................................................................ ii ACKNOWLEDGEMENTS ........................................................................................................... iii ABSTRACT ................................................................................................................................... iv LIST OF TABLES .......................................................................................................................... x LIST OF PLATES ......................................................................................................................... xi CHAPTER ONE ............................................................................................................................. 1 INTRODUCTION .......................................................................................................................... 1 1.1 Problem statement ............................................................................................................ 4 1.2 Justification ...................................................................................................................... 5 1.3 Hypothesis ........................................................................................................................ 6 CHAPTER TWO ............................................................................................................................ 7 2 LITERATURE REVIEW ....................................................................................................... 7 2.1 Rice Taxonomy and Botany ............................................................................................. 7 2.2 Rice production in Ghana. ................................................................................................ 7 2.3 Nitrogen transformation in flooded soils ....................................................................... 10 2.3.1 Soil nitrate accumulation ........................................................................................ 10 2.3.2 Loss of nitrate ......................................................................................................... 11 2.3.3 Ammonia volatilization .......................................................................................... 12 2.4 Nitrogen (N) fertilizer management in rice paddy fields ............................................... 13 2.5 Importance of Nitrogen in rice plant nutrition ............................................................... 13 2.6 Biochar ........................................................................................................................... 14 2.7 Definition of terms ......................................................................................................... 15 v University of Ghana http://ugspace.ug.edu.gh 2.7.1 Kiln ......................................................................................................................... 15 2.7.2 Feedstock ................................................................................................................ 15 2.7.3 Char ......................................................................................................................... 16 2.7.4 Charcoal .................................................................................................................. 16 2.7.5 Synthesis gas ........................................................................................................... 16 2.7.6 Biooil....................................................................................................................... 17 2.8 Biochar production processes......................................................................................... 17 2.9 Hydrothermal Carbonization. ......................................................................................... 18 2.9.1 Pyrolysis .................................................................................................................. 18 2.9.1.1 Slow pyrolysis ................................................................................................. 19 2.9.1.2 Fast pyrolysis ................................................................................................... 19 2.9.1.3 Gasification ...................................................................................................... 19 2.9.1.4 Carbonization................................................................................................... 20 2.9.2 Structural composition of biochar ........................................................................... 20 2.9.3 Properties of biochar ............................................................................................... 21 2.9.3.1 Physical properties of biochar ......................................................................... 21 2.9.3.2 Chemical properties of biochar ........................................................................ 22 2.9.4 Effects of feedstock on biochar properties.............................................................. 22 2.9.5 Effects of temperature on biochar properties .......................................................... 24 2.9.6 Nitrogen fertilizer and biochar interaction .............................................................. 25 CHAPTER THREE ...................................................................................................................... 29 3 MATERIALS AND METHODS .......................................................................................... 29 3.1 Soils and sampling ......................................................................................................... 29 3.2 Soil characterization ....................................................................................................... 29 3.2.1 Physical analyses .................................................................................................... 29 vi University of Ghana http://ugspace.ug.edu.gh 3.2.1.1 Bulk density determination .............................................................................. 29 3.2.1.2 Particle Size Analysis ...................................................................................... 30 3.2.2 Chemical analyses of soil........................................................................................ 32 3.2.2.1 Soil pH ............................................................................................................. 32 3.2.2.2 Total carbon and Total nitrogen ...................................................................... 32 3.2.2.3 Exchangeable bases and Cation Exchange Capacity ....................................... 33 3.2.2.4 Cation Exchange Capacity (CEC) ................................................................... 34 3.2.2.5 Exchangeable Acidity (H+ and Al3+). .............................................................. 35 3.2.2.6 Effective Cation Exchange Capacity (ECEC) ................................................. 36 3.2.2.7 Available Phosphorus ...................................................................................... 36 3.2.2.8 Total Phosphorus ............................................................................................. 37 3.3 Rice husk characterization ............................................................................................. 37 3.3.1 pH in water and KCl ............................................................................................... 38 3.3.2 Total carbon and Total nitrogen of rice husk .......................................................... 38 3.4 Biochar preparation and processing ............................................................................... 38 3.5 Biochar characterization ................................................................................................. 42 3.5.1 Biochar pH .............................................................................................................. 42 3.5.2 Biochar Total Nitrogen and Total Carbon .............................................................. 42 3.5.3 Biochar Total Phosphorus ....................................................................................... 42 3.5.4 Biochar Available Phosphorus ................................................................................ 43 3.6 Screen house studies....................................................................................................... 43 3.7 Experimental setup ......................................................................................................... 43 3.7.1 Pot filling with Soil and Biochar ............................................................................ 43 3.7.2 Experimental Data collection .................................................................................. 48 3.7.2.1 Growth Data .................................................................................................... 48 vii University of Ghana http://ugspace.ug.edu.gh 3.7.2.2 Plant Biomass yield ......................................................................................... 48 3.7.3 Chemical analyses of plant material ....................................................................... 49 3.7.3.1 Total Nitrogen and Carbon .............................................................................. 49 3.7.3.2 Nitrogen uptake ............................................................................................... 49 3.7.3.3 Total plant phosphorus .................................................................................... 49 3.7.4 Residual soil analysis .............................................................................................. 50 3.7.4.1 Residual Soil pH .............................................................................................. 50 3.7.4.2 Total Phosphorus for Residual soil .................................................................. 50 CHAPTER FOUR ......................................................................................................................... 53 4 RESULTS ............................................................................................................................. 53 4.1 Characterization of soil used .......................................................................................... 53 4.2 Chemical characterization of rice husk feedstock and its biochar derivative ................ 55 4.3 Characterization of Cow dung........................................................................................ 57 4.4 Soil amendment influence on rice growth parameters ................................................... 57 4.5 Dry matter and grain yields of rice plant as influenced by soil amendment and application of different nitrogen sources and levels .................................................................................... 59 4.6 Effects of biochar on N and P uptake ............................................................................. 64 4.7 Nitrogen levels and sources on nitrogen uptake............................................................. 64 4.8 Interactive effect of biochar and nitrogen on N and P uptake ........................................ 65 4.9 Influence of nitrogen sources and levels on residual soil chemical properties .............. 68 4.10 Effect of biochar and N interaction on Residual soil chemical properties ................. 68 5 DISCUSSION ....................................................................................................................... 71 5.1 Characteristics of native soil .......................................................................................... 71 5.2 Characteristics of rice husk and rice husk biochar. ........................................................ 72 5.3 Characteristics of Cow dung .......................................................................................... 74 viii University of Ghana http://ugspace.ug.edu.gh 5.4 Influence of amendments on Growth parameters .......................................................... 74 5.5 Influence of amendments on dry matter matter yield .................................................... 75 5.6 Influence of amendments on grain yield ........................................................................ 77 5.7 Influence of amendment on nutrient uptake. .................................................................. 78 5.8 Effects of amendments on residual chemical properties of soil ..................................... 80 5.9 Nitrogen Use Efficiency (NUE) ..................................................................................... 82 CHAPTER SIX ............................................................................................................................. 84 6 CONCLUSION AND RECOMMENDATION .................................................................... 84 6.1 Conclusion ...................................................................................................................... 84 6.2 Recommendations .......................................................................................................... 85 REFERENCES ............................................................................................................................. 86 ix University of Ghana http://ugspace.ug.edu.gh LIST OF TABLES Tables Page Table 3. 1 Fertilizer application rates ........................................................................................... 48 Table 4. 1 Some selected physical and chemical properties of the Lima series ........................... 54 Table 4. 2 Some chemical properties of the rice husk and its biochar derivative ......................... 56 Table 4. 3 Some chemical properties of cow dung used............................................................... 58 Table 4. 4 Effect of biochar application on plant height ............................................................... 58 Table 4. 5 Different sources and levels of N on weekly rice plant height* .................................. 58 Table 4. 6 Effect of biochar-nitrogen interactions on weekly plant height. ................................. 60 Table 4. 7 Influence of biochar on tiller numbers ......................................................................... 60 Table 4. 8 Effects of different sources and levels of N on tiller number ...................................... 60 Table 4. 9 Influence of biochar nitrogen interactions on tiller number ........................................ 61 Table 4. 10 Effects of amending soil with biochar and the influence on dry matter ................... 61 Table 4. 11 Nitrogen sources and levels on dry matter and grain yields of rice plant .................. 61 Table 4. 12 The influence of biochar x nitrogen interactions on dry matter and grain yields of rice ....................................................................................................................................................... 63 Table 4. 13 Effects of biochar on nutrient uptake ......................................................................... 65 Table 4. 14 Effects of different sources and levels of nitrogen on plant nutrient uptake ............. 65 Table 4. 15 Effects of biochar x nitrogen interactions on plant nutrient uptake ........................... 66 Table 4. 16 Influence of biochar on soil properties (residual soil). .............................................. 67 Table 4. 17 Influence of N on residual soil chemical properties .................................................. 70 Table 4. 18 Influence of biochar nitrogen interactions on residual soil chemical properties ....... 70 x University of Ghana http://ugspace.ug.edu.gh LIST OF PLATES Plate Page Plate 1 Locally manufactured kuntan kiln .................................................................................... 39 Plate 2 Rice husk feedstock under charring .................................................................................. 39 Plate 3 Partially charred rice husk biochar ................................................................................... 40 Plate 4 Completely charred rice husk ........................................................................................... 40 Plate 5 Water being sprinkled on biochar put off fire and to end up charring process. ................ 41 Plate 6 Picture of transplanted rice in pots.................................................................................... 47 Plate 7 Picture of potted rice plants at seven weeks of growth ..................................................... 47 xi University of Ghana http://ugspace.ug.edu.gh CHAPTER ONE INTRODUCTION Rice has become the second most consumed staple food in Ghana after maize and its consumption keeps increasing due to rising population, urbanization and change in consumer habits (National Rice Development Strategy, NRDS 2009; Global Agriculture Information Network, GAIN, 2010). According to Kranjac-Berisavljevic (2000), rice accounts for approximately 15% of the Gross Domestic Product (GDP) and its producing land size in Ghana totals about 45% of the total land area planted to cereals. The rice sector provides enormous employment to rural dwellers. A presentation on the National Rice Development Strategy (NRDS) for Ghana shows that the current per capita rice consumption in Ghana stands at 38 kg and this is expected to increase to 63 kg by the year 2018, leading to an aggregate demand of 1.68 million metric tons (NRDS, 2009). In spite of the increasing consumption of rice in Ghana, domestic demand for rice has not been adequately met by growth in local production, with average annual paddy and milled production of 493,000 tons and 322,000 tons respectively. The low productivity of rice has led to an importation of about 496,000 tons of milled rice in 2015 to compensate for the substantial rice yield gap (MoFA, 2015). This phenomenon has also created an opportunity for international food traders to supply rice to Ghana due to its high demand (Guisse, 2010). Current rice production in Ghana satisfied around 30 to 40 percent of the national demand with a corresponding average rice import bill of 450 million United State dollars annually (Angelucci, 2013; Kula & Dormon, 2009). Foreign exchange rate has significant impact on pricing of global rice trade due to price quoting in US dollars. The situation implies that a depreciating Ghanaian currency (cedi) relative to the US dollar, will require more Cedis for rice importation. This makes rice imports an issue of national concern for policy 1 University of Ghana http://ugspace.ug.edu.gh makers because of its impact on domestic currency and local industries (Awudu and Huffman, 2000). Rice production in Ghana has been categorized into three ecosystems based on adaptive mechanism which is characterized by water supply namely; irrigated, upland and lowland rice farming. Lowland ecosystem of rice production is of the largest among the ecosystems is the most appropriate environment suitable for rice cultivation in Ghana and constitutes about 78% of arable land. The ecology is characterized by traditionally growing crops without structures to regulate the flow of water. There is also minimal use of fertilizers and most often indigenous crop varieties are used (MoFA, 2009). The potential for lowland rice farming is much higher compared to upland rice farming because lowland presents the possibility of cultivating rice two or more times annually in the absence of irrigation which makes it economically more valuable compared to upland rice farming. However paddy yields under lowland are usually low as a result of a declining soil productivity (Buri et al 1999). Most rice farmers by way of improving the productivity of soils rely heavily on the use of inorganic fertilizers. However, the high cost of inorganic fertilizers make them unaffordable for most rice farmers to use. Alternatively, the adoption of an integrated approach that involves the use of fertilizers with other soil amendment could minimize the quantity of fertilizer used per unit area hence the cost. In rice growing areas in Ghana, rice husk abounds but is hardly used as organic matter because of its high C: N ratio (Issaka et al., 2011). There are thus ‘rice huskmountains’ in almost all rice growing areas in Ghana breeding rodents. Disposing of the rice husk has been through burning openly which causes environmental pollution. Alternatively, burning the rice husk under no or 2 University of Ghana http://ugspace.ug.edu.gh limited oxygen supply condition to produce biochar could serve as valuable soil conditioner to improve upon soil productivity. Biochar is a solid porous carbonaceous material produced by thermal combustion of organic material in an oxygen depleted atmosphere. It has physico- chemical properties that are suitable for safe and long term storage of carbon in the environment and for soil improvement (Shackley and Sohi, 2010). Biochar use in Ghana could offer new technology for both soil fertility and crop productivity improvement as well as potential positive and quantifiable environmental benefits, such as carbon trading (Yeboah et al., 2009, Major et al., 2010; Sohi et al.,2010; Gaskin et al., 2010; Bracmort, 2010). The application of biochar in combination with organic and inorganic fertilizers on tropical soils can lead to increased crop yields due to the ability of charred material to persist in soil for long periods (Glaser et al., 2002; Ogawa et al.,2006; Woolf, 2008). Numerous studies have also reported higher plant growth responses to the combined use of biochar with inorganic fertilizers signifying a synergistic relationship between the two soil amendments (Lehmann and Glaser, 2003). However, since the nitrogen content of biochar is low, plant nutrients must be supplied externally (Woods and Mann, 2000; Glaser and Birk, 2011). From long-term experiments, it has been also concluded that nitrogen (N) is the most essential nutrient element for rice, and usually it is the most yield-limiting nutrient in irrigated rice production around the world (Samonte et al., 2006). Additionally, inorganic nitrogen recovery rate within the tropics has been reported to be very low and mainly attributed to factors such as leaching (under flooded condition), untimely application of nitrogen fertilizers, method of placement, N source and soil fixation, (Nyalemegbe et al., 2012). 3 University of Ghana http://ugspace.ug.edu.gh Many sub-saharan African (SSA) farmers especially Ghanaian farmers are aware of the potential contribution of nitrogen to rice production. However, the use of nitrogen fertilizers in sub-Sahara Africa is very low compared to the world average (Woomer and Munchena, 1993). On the average, less than 5 kg/ha of inorganic fertilizer materials are applied to food crops in the sub-Sahara Africa (Tisdale et al., 2002). The low adoption of fertilizer has been attributed to high costs coupled with low producer price of most food crops. The constraints to inorganic fertilizer in Ghana call for investigation into the possibility of reducing the fertilizer N rates by combining the nutrient with conditioners to meet the N requirements of rice to increase yield. 1.1 Problem statement The current national average yield of rice is low and is estimated to be 2.7 Mt/ha (SRID, 2014). Low inherent soil fertility and declining soil productivity as a result of continuous cultivation has been recognized as some of the main causes of low yield in rice (Buri et al., 2011). The continuous decline in rice yields on smallholder farmers fields has led to a huge gap between potential crop yields and actual crop yields. Northern region is one of the regions noted for rice production under lowland ecology. Even though the region is the second highest rice producing region after Volta region, yield is low under lowland production (SRID MoFA, 2015). Rice farmers have relied on inorganic fertilizers to improve upon the fertility of soils within the region. Responses to inorganic fertilizers have been low because of low application rates. In addition, most of the nutrients especially nitrogen applied to these soils are lost through leaching due to the low CEC resulting from low input of organic matter and the inherently low clay contents of the soils. Organic fertilizers, on the hand, are very scarce in most of the rice growing areas in the Northern Region making their use limited in the rice growing communities. To achieve adequacy in rice production, hence reduction in rice 4 University of Ghana http://ugspace.ug.edu.gh imports, there is the pressing need to manage some of the soil infertility problems by adopting an integrated approach that is affordable to the rural poor farmer. 1.2 Justification Integrated approach of soil fertility management involving the use of biochar in combination with inorganic or organic fertilizers in Ghana is new and now being assessed in the perspective of the agricultural crop production system. The addition of biochar to soil has been reported to enhance soil cation exchange capacity, soil organic carbon, plant nutrient availability and fertilizer use efficiency due to reduced nutrient losses on highly weathered infertile tropical soils (Glaser et al, 2002; Lehman et al., 2003; Liang et al., 2006). Most of the research work on biochar in Ghana has been conducted on highly weathered Ultisols and Alfisols with little to no information on the Eutric Gleysol used in lowland rice production. Additionally, the effect of using biochar in combination with organic and inorganic N fertilizer in a bid to optimize N availability too has received little attention. In pursuance of the country’s goal of decreasing rice imports and making rice production more competitive, a critical study is required to evaluate the agronomic benefit of biochar prepared from rice husk on rice production vis-à-vis inorganic and organic N fertilizer application rates if the country’s quest for increased commercial rice production is to be realized. The use of rice husk biochar will additionally help to reduce CO2 emission to the atmosphere through the otherwise aerobic burning of the material. The use of rice husk biochar in rice production, if successful, will minimize rodent infestation of rice farms and mills and will furthermore be an attempt at closing the nutrient loop in rice production. 5 University of Ghana http://ugspace.ug.edu.gh The objectives of this study were therefore, to; i. Determine the influence of rice husk biochar in combination with different sources and rates of N on the growth and yield of rice. ii. Evaluate the influence of rice husk biochar on some chemical properties of a typic Eutric Gleysol after amendment for rice cultivation. iii. Evaluate the influence of rice husk biochar on nitrogen use efficiency. 1.3 Hypothesis HO: Rice husk biochar in combination with inorganic and organic N will not improve the growth and yield of rice and the chemical properties of a typic Eutric Gleysol. HA: Rice husk biochar in combination with inorganic and organic N fertilizer as amendments will improve growth and yield of rice and chemical properties of a typic Eutric Gleysol. 6 University of Ghana http://ugspace.ug.edu.gh CHAPTER TWO 2 LITERATURE REVIEW 2.1 Rice Taxonomy and Botany Rice is the second most cultivated grain crop in the world after maize (Boumas, 1985). There are two species of domesticated rice in the Poaccae family namely Oryza sativa and Oryza glaberrima (Linscombe, 2006). The Oryza sativa family is a native of tropical and subtropical southern Asia whiles oryza glaberrima is a native of Southeastern Africa (Linares, 2002). Oryza glaberrima is less yielding compared to Oryza sativa but resistant to several stresses (WARDA, 1996; Jones et al, 1997). Although they are distinctively different from each other, Oryza glaberrima and Oryza sativa are used as the background parents in varieties amelioration programmes. The rice crop is cultivated as a monocarpic annual grass with hairy auricle, jointed hollow round culms, flat, sessile leaf blades, and a terminal panicle. It has intercalary meristems that enable the crop grow vertically without lateral thickening and enable it survive as a perennial crop in tropical areas. It has the ability to produce ratoons and survive for about 20 years (Boumas, 1985). Depending on the crop variety and fertility status of the soil, the rice plant usually grows to 1.0 – 8 m tall producing small wind pollinated flowers in a branched arching to the pendulous inflorescence. 2.2 Rice production in Ghana. The two main rice varieties cultivated in Ghana are Oryza sativa and Oryza glaberima (Agbanyo 2012). Rice is cultivated in the ten regions of the country (MiDA, 2010). The crop is grown within all the main ecological-climatic zones with the Northern, Volta and Upper East regions being the 7 University of Ghana http://ugspace.ug.edu.gh main rice producing regions in the country producing an average paddy yield of 45,000 to 160,000 tons annually (MoFA, 2015; USAID, 2009). Rice production in Ghana is mostly dominated by smallholder farmers, with farm size below one hectare (Angelucci et al., 2013). Most of these small scale farmers rely on the use of low-quality seeds as planting materials for cultivation, which affects the growth pattern and results in irregular maturity time. This therefore affects harvest and rice grain quality (Angelucci et al., 2013). Women perform an important role in the rice production value chain. They are mainly involved in activities such as transplanting, manual weeding, fertilizer application and scaring of birds. Also, women carry out post-harvest operations like; packaging, threshing, hauling, winnowing, drying, parboili ng, milling, storage and marketing. Conversely, men predominantly carry out land preparation activities which encompass land clearing, ploughing, harrowing and also harvesting (Norman & Kebe, 2006). In Ghana, rice is cultivated in three different ecologies which comprise; upland rain-fed, lowland rain-fed, and irrigated ecologies. Lowland rain-fed ecology accounts for approximately 78% of the country’s rice production. Upland rain-fed and irrigated ecologies on the other hand produce about 6% and 16%, respectively (MoFA, 2009). Under the upland rain-fed ecology, the cultivation of rice is done on well drained soils with relatively low water table normally below the root zone of the plant. Precipitation is therefore the only source of moisture for crops in this ecology, consequently cultivation can only be done once in a year under mono-modal rainfall pattern areas (Kranjac-Berisavljevic et al., 2003). Weeds-crop competition is very intense in this ecology since the soil condition is suitable for most weeds. Short duration and drought tolerant varieties are predominantly grown in this ecology. Varieties of O. glaberrima are commonly grown due to their tallness and ability to compete effectively with weeds (Agbanyo, 2012). These varieties are well 8 University of Ghana http://ugspace.ug.edu.gh adapted to the harsh environmental conditions, diseases, insects, pests, and the low soil fertility (MoFA, 2009). Rain-fed lowland ecology is more suitable for rice production than the upland rain-fed ecology even though it also depends on rainfall. The soils within lowland ecology are able to retain more water during downpour due to their hydromorphic nature and the topography (Agbanyo, 2012). Generally, the field is levelled and bunded to conserve water from a downpour or other water bodies. Oteng (1997) reported that, rain-fed lowland ecology face constraints such as weed control, water management, and adverse soil conditions. Irrigated ecology utilizes technology such as improved land preparation, improved varieties, fertilizer application and water management. As a result, it gives higher yields than the other ecologies (MOFA, 2009). The crops are not dependent on rainfall since water is frequently supplied, thus the crop can be grown for two or more times in a year. In this ecology, weed competition is rarely seen as the field is continuously submerged to control weeds. Rice production in the country has been far lower than demand due to rapid population increase and changing consumer preferences (MiDA, 2010). This suggests that, the quantity of rice consumed in Ghana is more than the quantum produced in the country. To deal with this deficit, Ghana has to either increase its production or import rice into the country. Rice imports between 2003 and 2008 were 348,182 metric tons which accounted for 69% of the total national rice consumption needs (MiDA, 2010). Ghana produced about 30% to 40% of its rice requirement with a corresponding annual average rice import bill of USD 350 million (MOFA, 2015). The huge reliance on rice imports has been a worry for the Ghana government especially after food prices ascended in 2008. Ghana launched its National Rice Development Strategy (NRDS) in 2009 with the main objective of doubling domestic production by 2018. 9 University of Ghana http://ugspace.ug.edu.gh 2.3 Nitrogen transformation in flooded soils Under saturated or flooded conditions, nitrification is restricted by a limited O + 2 supply and NH4 accumulates in the soil. At the end of a flooded rice crop, organic N and NH + 4 N dominate and NO - 3 present is typically negligible. Subsequent drying of the soil favors aerobic N transformations. Organic N mineralizes to NH +4 , which is rapidly nitrified into NO - 3 . As a result, NO -3 accumulates in the soil during the aerobic phase, but is rapidly lost upon soil flooding (George et al., 1992). Plant growth can influence the magnitudes and forms of soil mineral N. Nitrate, the predominant form of soil mineral N during the nonflooded season, will be assimilated by plants growing during the dry season and dry-to-wet transition periods. Buresh et al. (1989) found that soil NO - 3 during the dry season in a lowland rice soil correlated inversely with the amount of N accumulated in weeds. Legumes grown during this season additionally accumulate atmospheric N through Biological Nitrogen Fixation (BNF). Part of the N in the plant biomass is removed from the land through the harvestable products of an economic crop. The remaining plant N can be returned to the soil as residues. Decomposition of plowed-under dry-season plant residues releases NH +4 into the flooded soil. Rice uptake decreases NH + 4 , the predominant N form in the flooded soil. Declining NH +4 level in flooded soil during the latter part of rice season is partly replenished through BNF in flooded soil (Eskew et al., 1981; Yoshida and Yoneyama, 1980) and from decomposition of rice roots and stubbles in addition to mineralization of soil N. 2.3.1 Soil nitrate accumulation Nitrate-N accumulates when lowland rice soils become dry and aerated (Patrick and Wyatt, 1964, Ventura and Watanabe, 1978). The production of NO -3 depends on the amount of organic N available for mineralization. Organic N varies considerably in lowland rice soils, depending on the level of native organic matter, and 10 University of Ghana http://ugspace.ug.edu.gh the history of cropping and organic amendments. The amount of N mineralized is increased by higher soil organic N levels (Broadbent, 1984; Hadas et al., 1986; Sahrawat, 1983). Bacon (1990) reported that successive soil incorporation of rice stubble gradually increased the N mineralization potential. Residual soil water from the preceding wet season rice crop, intermittent rains, and irrigation cause fluctuating soil water conditions. Soil water fluctuation generally results in a large production of NO -3 (Birch, 1960; Herlihy, 1979; Sahrawat, 1980; Seneviratne and Wild, 1985). In a greenhouse study, continuous soil flooding during the dry season prevented NO -3 accumulation (Ventura and Watanabe, 1978). Drying, as well as alternate drying and wetting treatments resulted in the accumulation of soil NO -3 . Dry-season fallows are subjected to tillage for upland crap establishment or for weed control. Tillage increases soil aeration and tends to enhance the nitrification of mineralized NH +4 into NO - 3 (Dowdell et al., 1983). 2.3.2 Loss of nitrate Flooding of aerated soil has generally been accepted as a major factor of NO -3 loss from rice soils (Buresh et al., 1989). With the use of 15N microplots, Bacon et al. (1986) reported 90% reduction in NO -3 concentration after flooding of a rice soil. Soil flooding can promote leaching losses of NO -3 . Downward water flow carries NO - 3 to lower soil layers (White, 1988). Large NO - 3 losses through leaching occur generally from aggregated soils and from soils under bare fallow (Legg and Meisinger, 1982; White, 1988). These conditions exist in lowland soils during the aerobic phase before puddling for rice culture. Soil saturation depletes soil of its O2, thus creating favorable conditions for denitrifying organisms to reduce NO -3 .Denitrification results in the production of N2 and N2O (Knowles, 1982). The rates of N2 and N2O evolution from soils will be higher under conditions of f1uctuating redox potentials (wetting and drying cycles) than when the redox potential is continuously high (aerobic condition) or continuously low (anaerobic condition) (Letey 11 University of Ghana http://ugspace.ug.edu.gh et al., 1981; Reddy and Patrick, 1975). Mosier et al. (1986) measured large fluxes of N2 and N2O from both fallow and cropped aerobic soils following water applications. Conditions favorable for N2 and N2O emissions may occur during the dry-to-wet transition period in lowland rice-based crapping systems. Bacon et al. (1986) attributed rice soil NO -3 loss primarily to denitrification. An incubation study with the use of 15N-labeled NO -3 by Buresh et al. (1989) indicated that NO - 3 completely disappeared after 9 days of flooding, and 5% or less of the added NO -3 remained in the soil as either NH +4 or organic N. 2.3.3 Ammonia volatilization Loss of nitrogen through volatilization from soils including flooded soils has been a subject of several recent comprehensive reviews. Mikkelsen et al. (1978) have reported the significance of NH3 volatilization as N loss mechanism in flooded rice fields. It is clearly evident from literature that estimates of the magnitude of NH3 volatilization loss may vary widely with the technique used for its measurement (De Datta, 1981). The pH of the flooded water has been recognized as the single most important determinant that affect NH3 volatilization (Jayaweera and Mikkelsen, 1990). The magnitude of NH3 loss from submerged soils is directly related to the content of aqueous NH3 or partial pressure of ammonia in water at the interface with the atmosphere. Aqueous NH3 as a fraction of total ammoniacal N is directly influenced by water pH and temperature. Aqueous NH3 is negligible below pH 7.5, but it increases rapidly from pH 7.5 to 10. At pH 9.2 about 50% of the ammoniacal N in water is present as NH3 (Vlek and Craswell, 1981). Aqueous NH3, at a constant ammoniacal N concentration and pH, increases linearly with temperature, resulting in nearly a fourfold increase with a change in temperature from 10 to 40°C (Vlek and Craswell, 1981). 12 University of Ghana http://ugspace.ug.edu.gh 2.4 Nitrogen (N) fertilizer management in rice paddy fields Nitrogen fertilizer is a very important nutrient for rice growth and development. To produce 11 to 22 kg of rice grain, 1 kg of N is needed (Duxbury et al. 2000). Apart from being the most essential nutrient element, it has also being observed that it is the most difficult nutrient element to manage in International Irrigation (IIR) rice growing ecology. (Liu et al., 2013). According to Cassman and Harwood (1995), nitrogen is extremely mobile in the soil and it is lost from the soil plant interface through different ways and this leads to low agronomic nitrogen use efficiency in rice production. However, Belder et al. (2005) found an increase in grain yield when nitrogen was applied at the right time in IIR system of rice production. Nitrogen deficiency during rice growth period reduces the crop biomass and increase the percentage of unfilled grains, thus reducing the grain yield (Mohammadian, 2002). Rezaei et al. (2009) reported that nitrogen fertilizer application increased plant height, number of panicles per meter square, harvest index and fertility percent. However, test weight, number of filled and unfilled grains and number of grains per panicle were not affected by nitrogen fertilizer application. 2.5 Importance of Nitrogen in rice plant nutrition Among the essential nutrient elements, nitrogen is the most vital nutrient influencing the potential yield of rice (Cassman and Harwood, 1995). At early and mid tillering stage of growth, rice plants need nitrogen as much as possible for maximum panicle production. Nitrogen is also required at the reproductive and ripening stages in order to enhance number of grains/panicle and grain filling (Datta, 1986). The amount of N removal is estimated between 16 to 17 kg for the production of one ton of rough rice (Dobermann and Fairhurst, 2000). The efficiency of nitrogen uptake ranges from 20 to 60% based on the growing ecology, pH and water temperature, doses and modes of N supply (split or 13 University of Ghana http://ugspace.ug.edu.gh blanket application) as well as varieties (Datta et al., 1986). Conversion of nitrogen in nitrogenous fertilizer to ammonium is essential in the nutrition of irrigated rice production (Dobermann and Fairhurst, 2000), although rice can also absorb nitrate-N (Singh et al. 2002). According to Singh et al. (2002), ammonium-N fertilizer sources are highly recommended in submerged rice growing ecology because the NH +4 is stable under flooded soil conditions. The availability of excessive N in the soil does not only cause higher transpiration rates but also reduces the availability of soil water particularly during flowering and grain filling stage which contributes to reduce grain yield (Song et al, 2010). Under pre flooded condition, the recommended rate of nitrogen application for attainment of nitrogen uptake of 130-150 kgN/ha is 120-180 kg at panicle initiation to produce grain yield of 12 t/ha of rice per hectare (Nangia, et al., 2008). 2.6 Biochar Biochar is the by-product of biomass pyrolysis in an oxygen depleted atmosphere. It contains porous carbonaceous structure and an array of functional groups (Lehmann and Joseph 2009). The product which is a mixture of various elements such as carbon, hydrogen, oxygen and in different proportions as properties which is dependent on material from which is produced and the thermal temperature (pyrolysis temperature) (Masek, 2009; Mukherjee et al., 2012; Zimmerman, 2012). Biochar is progressively receiving attention in agriculture as an environmental-friendly amendment to principally mitigate climate (Lehmann and Glaser, 2003). Biochar or black carbon is rich in ‘carbon’ has a large specific surface area and has been shown to have the ability to increase water and nutrient retention of soils (Lehmann and Joseph, 2009). It also enhances the productivity of soil by improving water holding capacity, nutrients adsorption and activity of microbes and therefore increasing yield of crops. Charring of feed stocks such as sawdust, animal 14 University of Ghana http://ugspace.ug.edu.gh manure and crop residues to produce biochar helps in recycling of forestry and agricultural wastes (Lehmann et al., 2003). 2.7 Definition of terms The process of biochar production is associated with a thermochemical process known as pyrolysis. Although biochar production started several years back, the science involved with its production is still poorly understood. The following list of terms have been defined to differentiate between the different terms associated with its production. These are: 2.7.1 Kiln Kilns are equipment constructed from soil or other local materials used in the production of biochar. Modern kilns can be constructed from metals such as oil drums designed in various forms to prevent oxygen entry. The ancient and simplest way of producing char since the dawn of carbonization history is the use of earth as biochar production kilns. The use of earth as barrier in carbonization process involves underground or surface. With the underground method, a dug pit is filled with firewood and then covered with excavated soil to serve as insulator for the pit whiles the surface method involves covering a pile of wood on the ground with sand to limit air entry (Lehmann & Joseph, 2009). 2.7.2 Feedstock Feedstock is any organic material pyrolysed to produce biochar. The physico-chemical properties of biochar produced is influenced by the type of feedstock from which biochar is produced. Organic materials such as wood waste, crop residues (including straw, nut shells, and rice hulls), switch grass, bagasse from the sugarcane industry, chicken litter are currently used as feedstocks in commercial scale or in research facilities (Das et al, 2008). 15 University of Ghana http://ugspace.ug.edu.gh 2.7.3 Char Char solid component of biochar product derived from thermal decomposition of organic material. It is made up of between 60 and 90% volatile and fixed carbon. The inorganic ash component of the char is made up of different mineral compounds with approximately 6.8 g phosphorus per kg char produced from wood materials most of which are bound to char with about 15% of the phosphorus which is soluble. (Lehman and Joseph, 2009). About 1% of nitrogen is contained in the char with the rest of as gas. In the case of potassium, about 50% is accessible from the char (Pyreg, 2013) 2.7.4 Charcoal It is solid material derived from the thermal decomposition of conversion of wood and other materials mainly used as source of fire for burning (Okimori et al., 2003). According to Harris (1999), biochar production process is similar to that of charcoal which can be considered as one of the oldest invented industrial technologies of Homo sapiens. However, biochar production can be differentiated from charcoal and other similar materials by considering the fact that biochar is synthesized completely with the intention of being applied to the soil for improving its fertility, carbon sequestration and other uses. In charcoal production, the burning of biomass in fire will create ash mainly consisting of minerals like calcium, magnesium or other inorganic carbonates in contrast to the organic carbon rich biochar. Moreover, only a limited amount of vegetation will be burnt in the conditions of limited oxygen supply, thus allowing a portion of it to remain as char. 2.7.5 Synthesis gas This is the gaseous by-product of pyrolysis comprising a mixture of gases such as carbon monoxide (CO), carbon dioxide (CO2), nitrogen (N2), and hydrogen (H2). Synthesis gas also contains 16 University of Ghana http://ugspace.ug.edu.gh methane (CH4), water vapour, some higher hydrocarbons, various inorganic and organic contaminants like char, ash, tar, ammonia (NH3), hydrogen sulfide (H2S), sulfur dioxide (SO2), and nitrogen dioxide (NO2) (Belgiorno et al, 2003) . Additionally, the gas contains impurities capable of causing serious problems with downstream applications by clogging the process lines, deactivating catalysts, and acting as precursors for toxic emissions (Nordgreen et al, 2006). Synthesis gas can be upgraded to produce fuels such as biomethane, DME (dimethyl ether) or methanol. (Bojler Görling, 2012). 2.7.6 Biooil The liquid part in the pyrolysis gas is called biooil and consists of long hydrocarbon chains. Biooil contains between 45% and 50% oxygen which is primarily bound in water. In the biooil more than 300 different compounds have been identified which also varies depending on the type of biomass and pyrolysis process. (Ringer et al., 2006) 2.8 Biochar production processes Carbonization of wood for the purpose of biochar production is known to human from time immemorial. By utilizing waste resources, enhanced biochar technology can contribute to mankind by providing energy needs of the future and also improving soil carbon sequestration potential. Biochar production entails heating of biomass in an oxygen deficient environment to remove volatile gases to porous carbon rich material by simple process is known as thermal decomposition usually achieved from pyrolysis or gasification (Demirbas, 2004). The artificial production of biochar generally utilizes two methods, hydrothermal carbonization and pyrolysis. In both charring processes, organic biomass substrates (feedstock, manure, straw, etc.) are converted to carbon rich products, due to thermochemical processes under limited or no 17 University of Ghana http://ugspace.ug.edu.gh available oxygen supply (Lehmann and Joseph, 2009). Different biomass contains different fractions of fixed carbon and different amounts of lignin, cellulose and other organic compounds that will degrade at different rates and respond differently to temperatures (Bridgwater, 2012). 2.9 Hydrothermal Carbonization. The hydrothermal carbonization of biomass is obtained by applying high pyrolytic temperature between 200 and 250 °C to a biomass in a suspension with liquid under high atmospheric pressure for several hours to produce a coal-like product called hydrochar (Funke and Ziegler 2010). The product which is usually characterized by high carbon content and high calorific value is produced from organic materials such as municipal solid waste, wet agricultural residues, sewage sludge, algae and aquaculture residues (Afolabi et al, 2015). In this process, the feedstock is introduced into water under mild temperature (usually in the range 180 – 250 °C and pressure (generally autogeneous) conditions. During hydrothermal carbonization, the biomass undergoes dehydration, decarboxylation and decarbonylation reactions: the biomass is converted into a carbon-densified product hydrochar, which can be used as soil amendment to improve soil nutrient retention capacity by increasing the nutrient supply for plants and decreasing losses due to leaching (Libra et al, 2011). 2.9.1 Pyrolysis Pyrolysis is the heating of organic materials at elevated temperature in an oxygen deficient environment. The products of pyrolysis are char, syngas (from synthetic gas) and bio-oil (Lehmann and Joseph, 2010; Antal and Gronli, 2003). The solid product, termed variously as char, biochar, charcoal or coke, is generally of high carbon content and may contain around half the total carbon of the original organic matter. The syngas, is the gaseous product and comprises a mixture of carbon monoxide, hydrogen and carbon dioxide can be recirculated into the pyrolyzer as a 18 University of Ghana http://ugspace.ug.edu.gh fluidizing gas or burned to provide energy for the pyrolysis process (Bojler Görling, 2012). Liquid products from biomass pyrolysis are frequently termed bio-oil. Pyrolysis can be divided into 5 categories depending on the operating conditions used i.e. temperature, residence time, heating rate and flow rate of sweeping gas. They include slow pyrolysis, fast pyrolysis, gasification and carbonization. 2.9.1.1 Slow pyrolysis This involves the slow heating of large biomass to temperatures in excess of 400 °C in an oxygen deficient environment to produce biochar. The residence time for feedstock in reaction is longer due to the relatively slow pyrolysis process resulting from slow transfer of heat. It yields more biochar than any other technology involved. It can preserve up to 50% of the carbon in the charred organic material (Garcia-Perez et al., 2011). 2.9.1.2 Fast pyrolysis This involves the rapid heating of biomass within few seconds or less at temperature range of 400 - 700 °C in an oxygen deficient environment. Fast pyrolysis which produces 60 to 70% of the biomass as bio oil and 15 to 25 % as biochar requires the particle size of feedstock to be generally less than 2 mm to attain the rapid heating rate (Cummer and Brown, 2002; Czernik and Brigwater, 2004; Mohan et al., 2006 ) . 2.9.1.3 Gasification The term gasification involves the thermo-chemical conversion of biomass at high temperatures (>700 °C) under limited amount of oxygen conditions to produce combustible gases known as syngas. The main constituents of the gases include carbon monoxide (CO), hydrogen (H2) and traces of methane (CH4). The production of syngas by gasification is more efficient than the direct 19 University of Ghana http://ugspace.ug.edu.gh combustion of the original fuel due its combustion at higher temperatures. In addition, corrosive elements like chloride and potassium are removed during gasification due to high-temperature, which results in the production of clean gas instead of problematic fuels (Higman and Burgt 2008). 2.9.1.4 Carbonization This process involves the conversion of biomass into carbon rich material. It represents various pyrolytic processes, similar to traditional process used for charcoal production. The temperature ranges from 280 °C to 500 °C. The biomass spontaneously breaks down and produces charcoal along with the production of some combustible and non-combustible gases (Walter 1985). 2.9.2 Structural composition of biochar Biochar is made up of stable carbon compounds formed by heating biomass is to temperatures between 300 to 1000 °C under limited oxygen concentrations. Feedstock type from which biochar is produced and pyrolysis condition influence the structural and chemical composition of the biochar (Sohi et al., 2009). The proportion of aromatic carbon in biochar increases with increase in charring temperature due to the relative increase in the loss of volatile matter. As charing begins, there is evaporation of water followed by hydrocarbons, tarry vapour, H2, CO and CO2. Subsequently, there is conversion of alkyl and O-alkyl and C to aryl C (Baldock and Smernik, 2002; Demribas, 2004: Darko, 2013). Around 330 ℃, poly-aromatic graphene sheets begin to grow laterally, at the expense of armophous carbon phase, and eventually coalesce. Above 600 ℃, carbonization which is removal of most carbon atoms becomes the dorminant process and consequent relative increase of the carbon content. Carbonisation can be made up to 90% by weight in biochars from woody feedstocks (Antal and Gronli, 2003; Demribas, 2004). 20 University of Ghana http://ugspace.ug.edu.gh 2.9.3 Properties of biochar Physicochemical properties of biochar mostly depend on two factors. They are, properties of feedstock used for production and final temperature. Depending on the starting material and process parameters (temperature, residence time, etc.), the biochar will obtain different physical and chemical structures that can modify the physical and chemical characteristics of the soil 2.9.3.1 Physical properties of biochar The biochar structure is amorphous, containing local crystalline structures of joint aromatic compounds (Graber et al., 2011). The carbon skeleton formed during pyrolysis of organic matter results in a high porosity of biochar, due to its sponge-like structure (Kumari et al., 2014). The voids are formed as pores present as macro- (>50 µm), meso- (2-50 µm) and micropores (<2 µm). The large proportions of micropores (<2 x 10-3 µm in diameter) is responsible for the increasing surface area, that can reduce the mobility of soil water (Lehmann and Joseph, 2009). The high porosity results in a low bulk density, which when incorporated into the soil in sufficient concentrations can reduce the total bulk density of the soil (Laird et al., 2010). Most biochar exhibits a large surface area, depending on the base material and treatment. For biochar obtained from pyrolysis, surface areas range from 20 m2g−1 (Chen et al., 2008) up to 3000 m2g−1 (Guo et al., 2002). The large surface area of biochar will increase the ion exchange capacity and the sorption of nutrients (Lehmann and Joseph, 2009). The amount of adsorbed water is directly dependent on the surface area, therefore biochars are able to adsorb large amounts of water. The process of water adsorption on the surface area of biochar is governed by the functional groups (Antal and Grønli, 2003). When added to the soil, biochar will increase the total soil surface area, which is one physical property that is believed to be responsible to overcome the problem of too much water held in clay 21 University of Ghana http://ugspace.ug.edu.gh soils, due to increased soil aeration, and increase the water content/water holding capacity in sandy soils (Lehmann and Joseph, 2009). 2.9.3.2 Chemical properties of biochar The chemistry of biochar is highly dependent on the biomass used, temperature during pyrolysis and residence time. However, all biochars are composed of condensed aromatic ring structures that become larger and even more condensed with increasing pyrolysis temperature. It is known that a range of functional groups exists on the surface of biochar, such as heteroatoms (hydrogen, oxygen, nitrate, phosphorus and sulfur), acidic carboxyl groups and other basic functional groups (chromenes and pyrenes) (Lehmann and Joseph, 2009). However, the presence of functional groups on the surface of biochar depends on the type of feedstock. Moreover, the overall assumption is that temperatures above 600 °C will decompose the functional groups through heat degradation (Jindo et al., 2014). Most biochars have a strong surface area charge and thereby a high cation exchange capacity (CEC) having both cation and anion exchange capacity (Gai et al., 2014). Mukherjee et al. (2011) stated that the surface properties of biochar lead to its potentially useful properties, such as contaminant control and the release and retention of nutrients. There is small variability for the pH between biochars, with typical values above seven (Verheijen et al., 2010). 2.9.4 Effects of feedstock on biochar properties Physical and chemical characteristics of biochar produced from various feedstocks vary from one another. The feedstock from which biochar is produced has effect on the chemical structure, yield and elemental compounds present in the biochar (Zhang et al., 2014). The feedstock type of biochar influences the variability and contents of elemental constituents of ash in biochar (Antal 22 University of Ghana http://ugspace.ug.edu.gh and Gronli, 2003). Lignocellulosic feedstocks yield high biochar and low yield of poor quality bio- oil, cellulose-rich feedstock tends to give low molecular weight organic acids, water and pyrolytic sugar rich bio-oils whiles feedstocks high in lignin gives higher energy bio-oil enriched with mono and oligo-phenols (Laird et al.,2011) Due to the loss of Carbon, hydrogen and Oxygen much of the mineral constituents of the feedstock are retained in the biochar produced (Amonette and Joseph, 2009). Concentrations of bases in biochar depend primarily on the mineral content of the biomass feedstock and will determine its credits for nutrients such as P, K+, Ca2+, and Mg2+ that may be given for agricultural applications of biochar (Laird et al., 2009). The elemental contents of biochar especially N and P vary considerably due to the characteristics of feedstock. Feedstocks such as animal manures, biosolids and sewage sludge have high contents of nitrogen, phosphorous, potassium and Sulphur. There has been reported decrease of 60 to 80% of nitrogen in biochars derived from sugarcane bagasse, sewage sludge, rice husk and cattle manure (Shinogi and Kanri, 2003). Sohi et al. (2010) reported that the difference in magnitudes of surface area, pores and functional groups in biochar as a result of the difference in the feedstock, and how it affects the sorption characteristics of biochar. Biochar produced from manure-based feedstock has a higher CEC than that of wood based feedstock (Singh et al., 2010), but the wood-based biochar has a higher saturated hydraulic conductivity (Lei and Zhang, 2013). Wood-based feedstocks produce biochar that are coarser and more resistant (Winsley, 2007). The pH of biochar is also affected by the feedstock type with wood-based biochar having high pH and stable carbon than manure and crop residue based biochar (Novak et al., 2013; Brewer and Brown, 2012). 23 University of Ghana http://ugspace.ug.edu.gh 2.9.5 Effects of temperature on biochar properties Biochars produced from the same feedstocks may not possess similar properties due to differences in production conditions such as pyrolysis temperature and more specifically the final combustion temperature. The structural and physicochemical properties of biochar, pore structures, such as surface area, surface functional groups and elemental composition, can also be affected by varying the pyrolysis condition, such as pyrolysis temperature, heating rate and residence time (Tang et al., 2013; Brewer et al., 2009) Various studies have indicated that there is a decrease in biochar yield with increase in pyrolysis temperature (DeSisto et al. 2010; Garcia-Perez et al. 2008; Keiluweit et al. 2010). The decrease in biochar yield is as a result of combustion of organic materials as well as depolymerization of cellulose and hemicellulose (Demirbas 2004; Cao and Harris 2010). According to Muradov et al. (2012), the decrease in biochar yield with increased charring temperature is due to increase in the rate of volatilization of organic compounds. The main factor governing the surface area of biochar is pyrolysis temperature. Day et al., (2005) reported an increase in surface area of biochar from 120 to 460 m2/g following an increasee in charring temperature from 400 to 900 ℃. Biochar produced under low temperature regimes may be suitable for regulating the release of nutrients contained in feedstock whiles biochar produced under high temperature regimes result in formation of materials similar to activated carbon (Ogawa et al., 2006). Additionally, the surfaces of biochar produced under low temperature conditions can be hydrophobic thereby limiting their ability to water storage within soil. Biochar produced under lower charring temperature contains volatile compounds that can seal pore spaces leading to lower biochar surface area. The pore sealing effect is however reduced under high temperature condition (>650 ℃) as there is burning of volatile matter at higher charring temperatures (Mukherjee et al., 24 University of Ghana http://ugspace.ug.edu.gh 2011). There is accessibility of surface pore spaces of biochar at temperatures between 650 and 750 ℃ due to volatilization of liquid components of biochar. Howerever, there is collapse in the micropore structure of biochar when temperature rises above 750 ℃ leading to decrease in surface area of biochar (Lua and Guo , 1998). The chemical properties of biochar are also greatly affected by temperature and heating rate. Angin (2013) reported an increase pH values of biochar following increased pyrolysis or charring temperature. Yuan et al. (2011) attributed the increase in pH values to the separation of basic salts from organic materials due to increase in pyrolysis temperature. The quantity of carbon in biochar increases with increase in charring temperature, while the oxygen and hydrogen content decrease with respect to carbon content (Chen et al. 2011; Chun et al. 2004). In addition, increasing the charring temperature lead to an increase the ash and fixed C contents, and to a decrease the content of volatile materials (Tag et al, 2016). Furthermore, the H/C and O/C ratios of biochar are affected by charring temperature with the ratios of H/C and O/C decreased with increasing temperature. Other properties such as porosity, surface area, surface functional groups and cation exchange capacity (CEC) of biochars (Sun et al, 2014). According to Lehmann (2007) the Cation Exchange Capacity (CEC) of biochar increases with increased charring temperature. Lakaria et al 2012, observed differences in nutrient composition of biochars made under varying pyrolytic temperature and duration. There is decrease in the volatile and Nitrogen component of biochar whiles an increase in ash and fixed carbon content following an increase in pyrolysis temperature from 400 ℃ to 600 ℃ 2.9.6 Nitrogen fertilizer and biochar interaction Biochar directly and indirectly alters plant nutrient availability in soil. There is an increasing evidence suggesting that biochar impacts a number of soil N reactions (Clough et al., 2013) and 25 University of Ghana http://ugspace.ug.edu.gh the effects is dependent on biochar feedstock and production condition, in addition to soil properties and environmental conditions. Biochar has been observed to affect N fixation (Mia et al. 2014), N mineralization or immobilization (Ameloot et al., 2015), increase or decrease nitrification (Ulyett et al., 2014), denitrification (Cayuela et al., 2013), or ammonia volatilization (Mandal et al., 2016). Biochar also alters nodulation by N-fixing bacteria in crops such as pea, soybean and red clover, leading to increased plant biomass production, in association with increased B and Mo concentrations in biochar-amended soils (Mia et al., 2014; Ogawa and Okimori 2010; Rondon et al., 2007). Rondon et al. (2007) evaluated the biological N2 fixation by common beans (Phaseolus vulgaris L.) through biochar additions and reported that proportion of fixed N by Rhizobium strains increased by 72% when 90 g biochar per kg of soil soil was added. Bean yield was also increased by 46% with 90 g biochar kg−1 soil in comparison to no biochar treatment. A stimulation of N mineralization has been observed as a consequence of labile C addition or a result of soil pH neutralization linked to the stimulation of microbial activity and abundance. Biochar-induced changes in N cycling differ substantially from potential lime-induced changes, as biochar may sorb NO -3 , NH3, NH + 4 and organic-N (Bai et al., 2015) as well as compounds such as phenolics that could otherwise inhibit nitrification (DeLuca et al., 2006). In addition, indirect mechanisms associated with soil microbial composition changes can be generated by the specific properties of biochar and thereby have strong implications for soil microbial N processing. Nitrification rates were accelerated by addition of biochar in two acidic arable soils (Zhao et al., 2014). He et al. (2016) also reported an increased nitrification activity in biochar-amended acid oxisol when exogenous NH +4 was added, suggesting that nitrification, after successive biochar applications, was not limited by nitrifier activity as was observed in unamended soils. 26 University of Ghana http://ugspace.ug.edu.gh Biochar is more resistant when applied to the soil. Upon addition of biochar to the soil, there is enhacement of nitrogen utilization from applied chemical fertilizer (Steiner et al., 2007 ; Widowati et al.,2011). The reduction in nitrogen loss is as a result of increased cation exchange capacity of soil following biochar addition (Chang et al., 2008; Masuilli et al., 2010). Biochar amendments in temperate soils have the potential to recover N from high nutrient waste products (e.g. sewage sludge, poultry litter, food waste) (Bridle and Pritchard, 2004). Direct fertilization occurs when a high nutrient biochar is added to soil, leading to increased nitrogen uptake by plants (Chan et al., 2008). Low-ash biochars indirectly improve nutrient retention in soils, for plant nutrients such as NH +, NO - + 2+ 2+ 2+ 2+4 3 , K , Ca , Mg , Zn and Cu , by increasing soil CEC (Gaskin et al., 2010; Kameyama et al., 2012; Major 2009; Van Zwieten et al., 2010). Many studies have reported that biochar incorporation could reduce inorganic N leaching and increase N retention in the soil (Major et al., 2012; Sun et al., 2017; Yao et al., 2012). The mechanisms underpinning the effects of biochar on N retention in soil are not well understood, but some potential processes have been proposed: a). Biochar has a high cation exchange capacity (CEC) (Ding et al., 2010; Nelissen et al., 2012) and changes the soil pH (Novak et al., 2009), leading to the direct absorption of NH + -4 and NO3 . b). Biochar can enhance the water-holding capacity (WHC) of the soil and thus reduce the total volume of leachate (Ouyang et al., 2013; Zheng et al., 2013). c). Due to microbial immobilization (Ippolito et al., 2012), biochar, especially when pyrolyzed at low temperatures, usually contains considerable amounts of labile carbon (Nelissen et al., 2012). This carbon can serve as a microbial substrate, resulting in microbial demand for inorganic N, which thereby immobilizes the N through biotic processes (Lehmann et al., 2003 Nelissen et al. 2012 and 2014; Zheng et al. 2013). Ammonia volatilization is another mechanism that accounts for the loss of fertilizer derived N. This process tends to increase 27 University of Ghana http://ugspace.ug.edu.gh following the addition of biochar (Reverchon et al., 2014; Yang et al., 2015) because most biochars have a high pH and serve as liming agents (Novak et al., 2009). Even though previous studies have focus on using biochar to improve soil fertility, there is limited information on how biochar interact with nitrogen sources under flooded conditions. 28 University of Ghana http://ugspace.ug.edu.gh CHAPTER THREE 3 MATERIALS AND METHODS 3.1 Soils and sampling The soil was sampled from the savanna zone in the Northern Region of Ghana. The area has an average annual rainfall of about 870 mm (MoFA, 2015). The soil used for the experiment is the Lima series classified as Eutric Gleysol by the Soil Research Institute (1990) according to the FAO/UNESCO classification system (1990). The soil was located at 10º28’29.0”N and 0º47’55.5”W. Soil samples used for the pot experiment were randomly taken from the plough layer (0 – 20 cm), bulked, homogenized and sub samples taken for routine characterization and pot experiment. Undisturbed samples were also taken for bulk density determination. The disturbed samples were air-dried and portions were ground to pass through a 2 mm sieve to obtain the fine earth fraction. The remaining soil was not processed (whole soil) and was used for pot experiment in a screen house. 3.2 Soil characterization 3.2.1 Physical analyses The soil physical properties that were determined included bulk density and particle size distribution. 3.2.1.1 Bulk density determination The surface of the soil from which the soil was to be sampled was cleared by removal of plant debris and a 2.5 centimeter radius core sampler of known height was driven into the soil. To avoid compaction, another core sampler of known length was placed on the core sampler in the soil and hit with a hammer until the other in the soil was completely buried. The buried core sampler was 29 University of Ghana http://ugspace.ug.edu.gh then carefully removed and extraneous soil around the core sampler was removed. The process was repeated three times to obtain three replicate for the soil sample. The samplers were trimmed of soil at the ends after which each soil in the sampler was placed into a moisture can for drying at 105 ºC in an oven for 24 hrs. The oven dry mass of each soil in the core sampler was then recorded. The volume of the core sampler was determined from its radius and height. The field bulk density of the soil was calculated as follows; M ⍴𝑏 = ……………………………………………….………..[3.1] (𝑘𝑔/𝑚3) (πd2⁄4)h Where ⍴𝑏= Bulk density of soil M= mass of soil = W2-W1 W2 = Weight in gram taken after oven drying the moisture can and its contents. W1 = Weight in gram of empty moisture can. π d2/4= area of core base d= diameter of core h= height of core (π d2/4) h= volume of core (i.e. volume of soil) 3.2.1.2 Particle Size Analysis Bouyoucos hydrometer method modified by Day (1965) was used to determine the particles size distribution of the soil samples. Forty grammes (40 g) of the fine earth was weighed into a dispersing bottle. The soil was treated with H2O2 (1:1 soil: solution) to destroy the organic matter 30 University of Ghana http://ugspace.ug.edu.gh after which 100 mL of 5% calgon (sodium hexametaphosphate) solution was added to form a suspension. The suspension was shaken on a reciprocating mechanical shaker for 2 hours to help disperse the soil into the various separates (sand, silt and clay). The suspension of was then transferred into a 1 L graduated sedimentation cylinder and distilled water added to reach the 1 L mark. A plunger was used to vigorously agitate the soil suspension and then allowed to stand. After five minutes, a hydrometer was immersed and the first hydrometer reading taken. The first hydrometer reading was for both silt and clay in suspension. The second hydrometer reading (density of clay only in suspension) was recorded after 5 hours. The suspension was directly transferred onto a 47 µm sieve to determine the quantity of sand in the mixture. The content on the sieve was washed thoroughly with tap water to get rid of any clay and silt particles and then transferred into a moisture can of known weight for oven drying at 105 ºC for 24 hours. The hydrometer readings at five minutes and five hours were also taken for the blank which contained 5% calgon only. A thermometer was used to record temperatures of the suspensions at both hydrometer readings and the readings were recorded. Temperature effects on density of the soil particles were accounted for by using the relation provided by Day (1965). For every 1°C increase in temperature, above 19.5 °C, there is an increase of 0.3 in the density of the particles in suspension. Correction for temperature = blank hydrometer reading – increase in weight of soil particles The concentration of the three separates were calculated as follows: hydrometer reading at 5 hrs % clay = × 100………………………………..……...[ 3.2 ] 40 g hydrometer reading at 5 min− hydrometer reading at 5hrs % silt = × 100……………...[3.3 ] 40 g 31 University of Ghana http://ugspace.ug.edu.gh weight of oven dried sample % sand = × 100………………………………………..[3.4 ] 40 g Where 40 = weight of soil sample in grams The particle size distribution values calculated were used to determine the textural class of the soils with the aid of the USDA textural triangle presented in the appendix. 3.2.2 Chemical analyses of soil 3.2.2.1 Soil pH The pH of the soil in water was determined by weighing twenty grams of soil into a beaker followed by addition of 20 mL of distilled water to obtain soil to water ratio of (1:1). This ratio was used to ensure enough volume of supernatant for immersion of electrode. The mixture was then stirred several times for about 30 minutes and allowed to stand for about an hour to enable most of the suspension to settle and also for the temperature of the suspension to equilibrate with the room temperature. The glass electrode pH meter (pH-mV-Temp PL-700PV) was standardized using two solutions of pH 4 and 7. The electrode was rinsed with distilled water and then immersed into the partly settled suspension and the reading on the pH meter recorded. The determination of pH of the samples was repeated using 1 M KCl solution according to the protocol outlined. 3.2.2.2 Total carbon and Total nitrogen The total carbon and nitrogen contents of the soils were determined using a Leco Trumac Carbon Nitrogen Sulphur version 1.3 Analyzer. Two hundred milligrams of the fine earth fraction of each soil was weighed into platinum crucibles and each mixed with 500 mg of comcat and placed in the furnace of the analyzer. The C and N concentrations in the samples were read after 6 minutes of combustion. 32 University of Ghana http://ugspace.ug.edu.gh 3.2.2.3 Exchangeable bases and Cation Exchange Capacity Ten grams (10 g) of the soil samples (2 mm sieved) were weighed into a 200 mL extraction bottles. Hundred (100 mL) of 1N ammonium acetate (NH4OAc) solution buffered at pH 7.0 was added. The bottles were covered with lid and then placed on a reciprocating shaker and shaken for 1 hr at 180 strokes per min. The soil suspension was then filtered through a No. 42 Whatman filter paper. The filtrates were used for the determination of Ca, Mg, K and Na. A 5 mL aliquot of the filtrates from section 3.2.2.3 was pipetted into 50 mL volumetric flask and deionized water added to reach the mark on the volumetric flask. The Perkin Elmer atomic absorption spectrometer (Analyst 800) was calibrated with the appropriate standards for Ca, Mg and Na respectively and the absorbance for each element determined. Exchangeable Na and K were calculated as: R × Vol.of extract ×103(g) × 102(cmol)×E Ca (cmol kg−1c ) = ………………………….….[3.5 ] Weight of soil ×106(µg)× 40 Where 40 = Atomic mass of Ca and R = AAS (Atomic absorption spectroscopy) reading in mgL-1 E = Charge of Ca −1 R × Vol.of extract × 10 3(g) × 102(cmol) ×E Mg (cmolckg ) = ………………………..….[3.6 ] Weight of soil ×106(µg)× 24 Where 24 = Atomic mass of Mg R = AAS (Atomic absorption spectroscopy) reading in mgL-1 E = Charge of Mg 33 University of Ghana http://ugspace.ug.edu.gh −1 R × Vol.of extract × 10 3(g)× 102(cmol) × E Na (cmolckg ) = 6 ………………….…………[3.7] Weight of soil × 10 (µg) × 23 Where, R = AAS (Atomic absorption spectroscopy) reading on mgL-1 23 = Atomic weight of Na E = Charge of Na The K content in the diluted soil extracts from section 3.2.2.3 were measured with the standardized flame photometer. The flame photometer was standardized to give a 100 full scale deflection at 10 mg/kg of K. The values obtained were then used to calculate the amount of potassium contained in the soils as shown in the formula below: −1 R × Vol.of extract × 10 3(g)× 102(cmol)× E K (cmolckg ) = …………………..…………[3.8] Weight of soil × 106(µg) × 39.1 Where, R is the flame photometer reading (ppm) 39.1 = Atomic weight of K E = Charge of K 3.2.2.4 Cation Exchange Capacity (CEC) The soil residues after filtration in section (3.2.2.3) was immediately leached with 50 mL portions of methanol into empty plastic bottles. The soils were leached again with 50 mL portions of acidified 1M KCl through a No. 42 Whatman filter paper into different plastic bottles. Each portion 34 University of Ghana http://ugspace.ug.edu.gh was added at a time and allowed to pass through, before adding the next portion. Ten millilitres (10 mL) of the leachates were then transferred into a Kjeldahl flask and 5 mL of 40% NaOH was added and distilled. The distillate was collected in 5 mL of 2% boric acid in a conical flask to about 30 mL and then back titrated against 0.01M HCl to determine the ammonium ion concentration. The CEC of the soil was estimated after determination of ammonium ion concentration in the filtrate. 3.2.2.5 Exchangeable Acidity (H+ and Al3+). Five (5) grammes of soil was weighed into a 100 mL extraction bottle and 50 mL of 1 M KCl solution was added. The bottle and its content were placed on a mechanical shaker and shaken for 1 hour. The soil suspension was then centrifuged and the supernatant decanted into an empty clean bottle. With the aid of a pipette, twenty millilitres (20 mL) aliquot was taken and transferred into a 100 mL conical flask, heated to near boiling point to drive out CO2, allowed to cool down and 2-3 drops of phenolphthalein indicator added for titration to a permanent pink end point against 0.01 M NaOH. The titre value was recorded as titre for both H+ and Al3+. Five millilitres of 4% NaF was added to the solution at the endpoint and back titrated against 0.01M HCl until a colourless end point was reached. The titre value was recorded as that for Al3+. (𝑚𝐿 𝑁𝑎𝑂𝐻 𝑠𝑎𝑚𝑝𝑙𝑒−𝑚𝐿𝑁𝑎𝑂𝐻 𝑏𝑙𝑎𝑛𝑘)𝑥𝑁𝑥100 cmolc/kg KCl acidity = …………………………..……[3.9] 𝑠𝑎𝑚𝑝𝑙𝑒.𝑔 𝑚𝑙 𝐻𝐶𝑙𝑥𝑁𝑥100 cmolc/kgKCl exchangeable Al = …………………………………………….….[3.10] 𝑠𝑎𝑚𝑝𝑙𝑒.𝑔 cmolc/kgH = KCl exchangeable acidity – KCl exchangeable Al………………………....….[3.11] 35 University of Ghana http://ugspace.ug.edu.gh 3.2.2.6 Effective Cation Exchange Capacity (ECEC) The Effective Cation Exchange Capacity is obtained by summing up the exchangeable Ca2+, Mg2+, Na+, K+, H+, and Al3+. (i.e. Ca2++ Mg2++ Na++ K++ H++Al3+) 3.2.2.7 Available Phosphorus The available phosphorus in the soil samples were determined using the method of Bray and Kurtz, (1945). Fifty millilitres of Bray 1 solution (0.03 M NH4F in 0.025 M HCl) was added to five grams (5g) of soil in an extraction bottle. The soil suspension was shaken for 3 min on a reciprocating shaker at 180 strokes per min, allowed to settle and the supernatant was filtered into a 100 mL volumetric flask through a No. 42 Whatman filter paper then distilled water added to reach the mark. Phosphorus in the filtrate was determined using the Murphy and Rilley method (1962) molybdate blue-ascorbic acid colour development method as follows: A solution of 12 g of ammonium molybdate and 0.2998 g of antimony potassium tartrate dissolved in 250 mL of distilled water was prepared and added to 1000 mL of 2.5 M H2SO4 mixed thoroughly and made to volume in a 2 L volumetric flask and labelled Reagent A. Another solution was prepared by dissolving 1.056 g of ascorbic acid in 200 mL of Reagent A and labelled as Reagent B. Five millilitre (5 mL) aliquots of the filtrates were pipetted in duplicate into a 50 mL volumetric flask and the pH adjusted with p-nitrophenol indicator. The solution was then neutralized with a few drops of ammonium hydroxide (4M NH4OH) until the colour changed to yellow. Eight millilitres (8 mL) of Reagent B was then added to the sample solution and made to volume in a 50 mL volumetric flask. A blank was also prepared using 5 mL of distilled water and 8 mL of reagent B. The Spectroquant® Pharo 300 M spectrophotometer was calibrated using 5, 10, 15, 20, 25 and 30 mg L-1 standard P solutions prepared in the same manner as above. Phosphorus in the solution 36 University of Ghana http://ugspace.ug.edu.gh was determined by reading the resultant colour intensity on the Spectroquant® Pharo 300 jM spectrophotometer, at a wavelength of 712 nm. The available P concentration in the soil sample was read and calculated using the spectrophotometer reading as follows spectrophotometer reading (𝑚𝑔𝐿−1)× volume of extract P (mg/kg) = × 100…………...…..[3.12] volume of aliquot × weight of soil sample × 106 3.2.2.8 Total Phosphorus Total phosphorus was determined by digesting 2 g of 0.5 mm sieved soil with 25 mL of a mixture of concentrated HNO3 and 60% HClO4 in a ratio of 2:3 (HNO3 : HClO4). The digestion was continued until white fumes of HClO4- ceased. The digest was cooled, diluted with distilled water and then filtered into a 100 mL volumetric flask using a No. 42 Whatman filter paper. The volume was brought to the 100 mL mark with distilled water. The total phosphorus in the filtrate was measured by colour development and read on Philips PU 8620 spectrophotometer as described in section above (3.2.2.7) and the determination of P in soil sample was calculated using equation below spectrophotometer reading (𝑚𝑔𝐿−1)× volume of extract P (mg/kg) = ………………………. [3.13] volume of aliquot × weight of soil sample 3.3 Rice husk characterization Rice husk was collected from a rice processing mill at the Irrigation Development Authority at Ashaiman in the Greater Accra Region of Ghana. The feedstock was air-dried, milled to pass through a 0.5 mm sieve and saved for chemical analysis. 37 University of Ghana http://ugspace.ug.edu.gh 3.3.1 pH in water and KCl One gram of rice husk was weighed into a beaker and 20 mL of distilled water added, to give rice husk water ratio of (1:20). This ratio was used to allow enough volume of supernatant for immersion of electrode. After continuous stirring for 30 minutes, the mixture was allowed to stand for an hour to allow the suspension to settle and the suspension temperature to equilibriate with the temperature of the room. The glass electrode pH meter- CG818, Schott Great was standardized using two solutions of pH 4 and 7. The electrode was rinsed with distilled water and then dipped into the partly settled suspension and the reading on the pH meter taken. The determination of pH of the samples was repeated using 1 M KCl solution according to the protocol outlined. 3.3.2 Total carbon and Total nitrogen of rice husk The total carbon and nitrogen content of the rice husk were determined using a Leco Trumac Carbon Nitrogen Sulphur version 1.3 Analyzer. Two hundred milligrammes of the rice husk was weighed into platinum crucibles and each mixed with 500 mg of comcat and placed in the furnace of the analyzer. The total N and C concentration in the samples were read after 6 minutes of combustion. 3.4 Biochar preparation and processing The biochar was produced using locally fabricated conically shaped metal called the Kuntan Kiln (plate 1). The process involved placing the kiln on a flat cemented platform as shown below. The flame was then set up within the kiln using pieces of dried grasses and wood. The flame provided energy for the pyrolysis. When the flame finally lit up, the feedstock (rice husk) was gathered around the base of the kiln. 38 University of Ghana http://ugspace.ug.edu.gh Plate 1 Locally manufactured kuntan kiln Plate 2 Rice husk feedstock under charring The charring process started 10 to 15 minutes later when the rice husk feedstock started browning at the neck. The feedstock was turned thereafter every ten to fifteen minutes to obtain uniformly charred material and minimize the production of ash. During the charring process, a dual laser infrared thermometer was pointed to the heap to note the charring temperature which was between 537.2 ℃ and 628.1 ℃. The charring lasted between 40 to 50 minutes. 39 University of Ghana http://ugspace.ug.edu.gh Plate 3 Partially charred rice husk biochar Plate 4 Completely charred rice husk 40 University of Ghana http://ugspace.ug.edu.gh The biochar was then spread evenly on the cemented platform at the end of charring and water sprinkled on it to put off the fire and to end the charring process. The biochar was then rinsed with distilled water several times to get rid of the ash and then air dried. The biochar yield from charring of rice husk feed stock was estimated as follows 𝐷𝑟𝑦 𝑤𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑏𝑖𝑜𝑐ℎ𝑎𝑟(𝐷𝐵) 𝐵𝑖𝑜𝑐ℎ𝑎𝑟 𝑦𝑖𝑒𝑙𝑑(𝐵𝑦) = × 100% ……………….……….. [3.14] 𝐷𝑟𝑦 𝑚𝑎𝑡𝑡𝑒𝑟 𝑤𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑓𝑒𝑒𝑑𝑠𝑡𝑜𝑐𝑘(𝐷𝐹) The biochar was then grounded to pass through a 2 mm sieve and saved for routine chemical analyses Plate 5 Water being sprinkled on biochar to put off fire and to end up charring process. 41 University of Ghana http://ugspace.ug.edu.gh 3.5 Biochar characterization Samples of the prepared biochar was taken to the laboratory after air drying and sieving through a 2 mm sieve for analysis to determine some chemical properties. 3.5.1 Biochar pH Two grams (2 g) of biochar was weighed in triplicate into 50 mL beakers and 20 mL of deionized water was added to give a biochar to water ratio of 1: 10. The suspension was stirred continuously for 30 min, left to stand for 1 hour to equilibrate with room temperature. The glass electrode pH meter (pH-mV-Temp PL-700PV) was standardized using pH solutions of 4 and 7. The electrode was dipped into partly settled suspension of biochar and the reading on the pH meter taken. The same procedure was used to determine the pH of the biochar in 1 M KCl. 3.5.2 Biochar Total Nitrogen and Total Carbon The total carbon and nitrogen content of the biochar were determined using a Leco Trumac Carbon Nitrogen Sulphur version 1.3 Analyzer. Two hundred milligrammes of the rice husk biochar was weighed into platinum crucibles and each mixed with 500 mg of comcat and placed in the furnace of the analyzer. The total N and C concentrations in the samples were read after 6 minutes of combustion. 3.5.3 Biochar Total Phosphorus Total phosphorus was determined by digesting 0.2 g of biochar with 25 mL of a mixture of concentrated HNO3 and 60% HClO4 in the ratio of 1:1.5 (HNO3: 60% HClO4). Distilled water was added to the digest, filtered and made up to volume in a 100 mL volumetric flask with distilled water. The total Phosphorus in the digest was determined as described by the Murphy and Rilley method (1962) method as outlined earlier in section (3.2.2.7). The P content of the samples in 42 University of Ghana http://ugspace.ug.edu.gh triplicates was then read with the spectrophotometer, and the calculations were done as follows: spectrophotometer reading (𝑚𝑔𝐿−1)× volume of extract Total P (%) = ……………..……[3.13] volume of aliquot × weight of biochar 3.5.4 Biochar Available Phosphorus Fifty milliliters (50 mL) of 0.5 M NaHCO3 solution was added to one gramme of biochar contained in an extraction bottle and mixture shaken for thirty minutes on a mechanical shaker. The biochar extractant mixture was filtered through a Whatman No. 42 filter paper. A 10 mL aliquot was taken and 10 mL sulphuric acid (H2SO4) added and centrifuged at 3000 rpm for 15 minutes. The concentration of the P in each sample was then determined after colour development using the Murphy and Rilley method (1962) method as described in section (3.2.2.7). The intensity of the colour developed at a wavelength of 712 nm was read on the UV spectrophotometer and recorded. The P was then calculated as in equation [3.13] above. 3.6 Screen house studies Pot experiment was conducted in a screen house at the “Sinas Garden” of University of Ghana, Legon. Temperature in the screen house throughout the experiment was between 25 oC and 32 oC The potted plants were put in a screen house to control environmental conditions. 3.7 Experimental setup 3.7.1 Pot filling with Soil and Biochar Polyvinyl (PVC) containers of 17 cm diameter and a height of 17 cm were used as pots in the study. A total of 66 pots were used in the study. The pots were filled with soil to a predetermined height to attain the field bulk density value of 1.34 g/cm3 .Since the field bulk density and volume of pots were known, the weight of soil needed to fill the pot to get the required bulk density was calculated using the equation below. 43 University of Ghana http://ugspace.ug.edu.gh 𝑉 = 𝜋𝑟2h ;…………………………………..………[ 3.14 ] M (g) =𝐵𝐷 (g/cm3) x 𝑉 (cm3) ………………...…....[3.15 ] Where V is volume of cylindrical PVC pot, r, is radius of PVC pot, h, is height of pot, M, is the mass of soil sample and BD is soil field bulk density of soil . The mass of the soil from the calculation in equation [3.14] was 3.5 kg. This amount of soil was put into the pots leaving height of 5.5 cm in the pots to maintain a constant head of water simulating flooded conditions as in lowland conditions for rice cultivation. Half of the number of the potted soils were amended with biochar at a rate of 50 t/ha of biochar (i.e 30 t/ha of C in biochar). These treatments were replicated three times. All the soils were and then filled with water to field capacity and incubated for 2 weeks and randomized in the screen house. There were thus two levels of biochar application viz., 0 and 50 t/ha. The rice variety (Jasmine 85) planting stock was obtained from Savanna Agricultural Research Institute (SARI), Nyanpkala in the Northern Region. The seeds were air – dried for three (3) days, sieved and cleaned of debris. Germination test was conducted before planting which. The seeds were nursed in a nursery and transplanted 12 days after seeding and later thinned to 3 seedlings per pot. Fertilizer were applied to pots one week after transplanting. Two sources of N i.e. cow dung and ammonium sulphate were applied at three rates of zero (0), 50 kg N/ha and 100 kg N/ha to the soils. The quantity of cowdung (Q) applied per pot for the organic N sources was determined from the formula 44 University of Ghana http://ugspace.ug.edu.gh Q = RxA C Where R = Rate of application of N A = area of soil in pot (m2) C = nitrogen concentration of cowdung or ammonium sulphate R= 100 kg N per ha, Area (A) for pot of diameter 17 cm = 0.0227 m2 C = 1.2% Therefore, for cowdung N applied 100 kg per ha, Q = 0.0189 kg = 18.91g/pot Therefore for cowdung N at 50 kg per ha, using the formula above will be 9.45 g. A similar calculation was made for treatments requiring inorganic N fertilizer i.e. ammonium sulphate. Basal P and K fertilizers were applied to all the experimental treatments a rates of 40 kg K/ha and 45 kg P2O5/ha, respectively from muriate of potash and TSP. There was thus a two biochar rate, two N sources, three N rates and three replicates i.e. 2x2x3x 3 factorial experiment arranged in a completely randomized design giving 36 treatment units. Another set of 36 was added raising the number of experimental units 72 out of which 36 were harvested 48 days after transplanting and the remaining 36 harvested after 94 days. T1: B0ON0 0 t/ha rice husk biochar + 0 kg Organic N T2: B0IN0 0 t/ha rice husk biochar + 0 kg Inorganic N T3: B0ON50 0 t/ha rice husk biochar + 50 kg Organic N 45 University of Ghana http://ugspace.ug.edu.gh T4: B0ON100 0 t/ha rice husk biochar + 100 kg Organic N T5: B0IN50 0 t/ha rice husk biochar + 50 kg Inorganic N T6: B0IN100 0 t/ha rice husk biochar + 100 kg Inorganic N T7: B1ON0 50 t/ha rice husk biochar + 0 kg Organic N T8: B1IN0 50 t/ha rice husk biochar + 0 kg Inorganic N T9: B1ON50 50 t/ha rice husk biochar + 50 kg Organic N T10: B1ON100 50 t/ha rice husk biochar + 100 kg Organic N T11: B1IN50 50 t/ha rice husk biochar + 50 kg Inorganic N T12: B1IN100 50 t/ha rice husk biochar + 100 kg Inorganic N The boldly typed treatments were practically the same so two out of the four were used for the analysis thereby reducing the number of treatments to 10. 46 University of Ghana http://ugspace.ug.edu.gh Plate 6 Picture of transplanted rice in pots Plate 7 Picture of potted rice plants at seven weeks of growth 47 University of Ghana http://ugspace.ug.edu.gh Table 3. 1 Fertilizer application rates Fertilizer Nutrient supplied Rate Amount per pot (kg/ha) (g) Sulphate of ammonia Nitrogen 100 1.08 Cowdung Nitrogen 100 18.91 Triple super phosphate Phosphorus 45 0.23 Muriate of potash Potassium 40 0.15 A parallel experiment with the same treatments was set up in which case the experiment was terminated at seven weeks. After transplanting a 5.5 cm head of water was maintained to simulate flooded conditions 3.7.2 Experimental Data collection Plant growth was monitored after transplanting and data on growth parameters taken. After harvesting the dry matter weight was recorded followed by chemical analysis on the biomass to determine some nutrient contents of the straw. 3.7.2.1 Growth Data Plant height and tiller numbers were recorded weekly for 7 weeks as growth data. Plant height was measured with a meter ruler from the soil surface to the arch of the uppermost leaf. The tiller numbers were recorded by counting the total number of tillers week after week. 3.7.2.2 Plant Biomass yield Biomass was measured by harvesting the above ground biomass of rice plant from each pot at the end of the 48th and the 94th days of transplanting the rice. On the 48th day after sampling, the dry weight of the straw was noted after oven drying under temperature of 65 ºC for 3 to 5 days. On the 48 University of Ghana http://ugspace.ug.edu.gh 94th day after sampling the rice plants, grains were separated from the straw and the grains were air dried. The straw was oven dried for 3 to 5 days at 65 ºC to a constant weight. On the 94th day after sampling the rice plants, grains were separated from the straw and the grains were air dried. The straw was oven dried for 3 to 5 days at 65 ºC to a constant weight. The total biomass yield was calculated by summing the dry weight of the straw and grain. 3.7.3 Chemical analyses of plant material The harvested plant samples were subjected to chemical analysis to determine some chemical properties of the harvested plant samples 3.7.3.1 Total Nitrogen and Carbon The total carbon and nitrogen contents of the plant samples were determined using a Leco Trumac Carbon Nitrogen Sulphur version 1.3 Analyzer. Two hundred milligramme of the plant sample was weighed into platinum crucibles and each mixed with 500 mg of comcat and placed in the furnace of the analyzer. The C and N concentrations in the samples were read after 6 minutes of combustion in a mixture of helium and oxygen gas. 3.7.3.2 Nitrogen uptake The N uptake by plant was calculated using the formula below shoot % N Shoot N uptake (mg/pot) = shoot dry weight (g⁄pot) × × 1000………..[3.16] 100 3.7.3.3 Total plant phosphorus Hundred milligrammes of each of the milled shoot and root samples were weighed into 50 mL conical flask and 5 mL of concentrated sulphuric acid (H2SO4) was added. The flask was then swirled to ensure that the acid mixed thoroughly with the milled sample and left to stand overnight. 49 University of Ghana http://ugspace.ug.edu.gh This allowed for a thorough dissolution of the samples by the acid. The flask and its content were then heated on a sand bath for 1 min and H2O2 was added drop wise with intermittent swirling till the solution was clear. Deionized water was added to the solution and left to cool, after which the solution was filtered through a No. 42 Whatman filter paper into a 100 mL volumetric flask and made to the mark with deionized water. A 5 mL aliquot of the digest was pipetted into 50 mL volumetric flask in duplicates and colour developed according to the method of Murphy and Riley (1962) as outlined in section 3.2.2.7. The shoot total P was determined from the dry matter yield of plant and the plant P% content as: shoot % P Shoot P uptake (mg/pot) = shoot dry weight (g⁄pot) × × 1000 .…..[3.17] 100 3.7.4 Residual soil analysis Soils were sampled from the pots after harvesting of rice and analysed to determine some chemical properties. 3.7.4.1 Residual Soil pH Twenty grams (20 g) of the soil sample were weighed in duplicates into 50 mL beakers, Distilled water of 20 mL was added to the samples and stirred continuously for 30 min. The soil suspension was then left to stand for an hour. The glass electrode pH meter (pH-mV-Temp PL-700PV) was standardized and the pH measured as described in section 3.2.2.1. The pH in 1M KCl was also determined. 3.7.4.2 Total Phosphorus for Residual soil Total phosphorus for the residual soil was determined by digesting 0.2 g of residual soil with 25 mL of a mixture of concentrated HNO3 and 60% HClO4 in the ratio of 1:1.5 (HNO3: 60% HClO4). 50 University of Ghana http://ugspace.ug.edu.gh Distilled water was added to the digest, filtered and made up to volume in a 100 mL volumetric flask with distilled water. Phosphorus in the digest was determined as described by the Watanabe and Olsen (1965) as outlined in section 3.2.2.7. The P content of the samples in triplicates was then read with the spectrophotometer, and the calculations were done. Total Nitrogen and Total Carbon The total carbon and nitrogen content of the residual soils were determined using a Leco Trumac Carbon Nitrogen Sulphur version 1.3 Analyzer. Two hundred milligramme of the fine earth fraction of each soil was weighed into platinum crucibles and each mixed with 500 mg of comcat and placed in the furnace of the analyzer. The C and N concentration in the samples were read after 6 minutes of combustion. Total Phosphorous Residual phosphorus in the soil samples after harvesting the rice plant was determined. Ten grams of the air dried soil samples (2 mm sieved) were weighed into 100 mL extraction bottles. Fifty millilitres (50 mL) of Bray 1 solution (0.03 M NH4F in 0.025 M HCl) was added. The soil suspension was shaken for 3 min on a reciprocating shaker at 180 strokes per min, allowed to settle and the supernatant filtered through a No.42 Whatman filter paper into a 100 mL volumetric flask which was made up to the mark with distilled water. Phosphorus in the filtrate was determined using the Watanabe and Olsen, (1965) molybdate blue-ascorbic acid method as described in section earlier section (3. 2. 2. 7). Data Analyses The measured crop parameters, nutrient uptake and the residual soil analyses after harvest were subjected to analysis of variance (ANOVA) using Genstat 12th edition to establish if there were 51 University of Ghana http://ugspace.ug.edu.gh any significant difference in treatment effects at p˂ 0.05. Mean separations were done using LSD (0.05). 52 University of Ghana http://ugspace.ug.edu.gh CHAPTER FOUR 4 RESULTS 4.1 Characterization of soil used Some physico- chemical properties of the ploughed layer of the soil used in the study are shown in the Table 4.1 The soil is Lima series and is classified as Eutric Gleysol by the Soil Research Institute 1999 according to the FAO/UNESCO classification system (1990) or Aquic Dystroquept according to (USDA) (Dowuona, 1985). The sand content is 32.75%, silt 38.50% and clay content of 28.75% giving it a textural class of clay loam. The soil has bulk density of the ploughed soil layer is 1.34 Mg/m3. The soil is strongly acid in reaction with pH in water being 5.0 and in 1M KCl, the pH of the soil sample was 4.1 i.e. very strongly acid. The soil has an organic carbon content of 13 g/kg which is higher than the levels in most soils from the savannah zone of northern Ghana where the average carbon contents are generally lower than 5 g/kg (Nartey et al., 1997). The total nitrogen of 0.8 g/kg and available P of 10.76 mg/kg are consequentially higher than the average of most northern Ghana soils (Table 4.1). The C: N ratio of the soil is 16.25. The total phosphorus of the soil series is 124.5 mg/kg which is also characteristic of northern Ghana soils (Nartey et al., 1997). The exchangeable calcium and magnesium contents of the soil sample are 1.8 cmol/kg and 0.32 cmol/kg respectively. The exchangeable potassium is 0.49 cmol/kg whilst the exchangeable sodium the lowest among the exchangeable bases is 0.22 cmol/kg. The soil has an exchangeable acidity (Al3+ and H+) of 0.62 cmol/kg. The effective cation exchange capacity (ECEC) of the soil is therefore very low with a value of 3.46 cmol/kg with a high base saturation of approximately 83%. 53 University of Ghana http://ugspace.ug.edu.gh Table 4. 1 Some selected physical and chemical properties of the Lima series Properties Values Physical properties Bulk density (Mg/m3) 1.34 Sand content (%) 32.75 Clay content (%) 28.75 Silt content (%) 38.50 Textural class Clay loam Chemical properties pH 1:1 (H2O) 5.00 pH 1:1 (1M KCl) 4.10 Organic C (g /kg) 13.00 Total N (g /kg) 0.80 C: N 16.25 Total P (mg/kg) 124.50 Available P (mg/kg) 10.76 Exchangeable Ca (cmol(+)/kg 1.80 Exchangeable Mg (cmol(+)/kg 0.32 Exchangeable K (cmol(+)/kg 0.49 Exchangeable Na (cmol(+)/kg 0.22 Exchangeable Acidity cmol(+)/kg 0.62 ECEC 3.42 Base saturation (%) 82.70 54 University of Ghana http://ugspace.ug.edu.gh 𝐷𝑟𝑦 𝑤𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑏𝑖𝑜𝑐ℎ𝑎𝑟(𝐷𝐵) 𝐵𝑖𝑜𝑐ℎ𝑎𝑟 𝑦𝑖𝑒𝑙𝑑(𝐵𝑦) = × 100% ……………….……….. [3.14] 𝐷𝑟𝑦 𝑚𝑎𝑡𝑡𝑒𝑟 𝑤𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑓𝑒𝑒𝑑𝑠𝑡𝑜𝑐𝑘(𝐷𝐹) 11.5 𝐵𝑦 = × 100% = 57.5%.....................................................................[3.15] 20 4.2 Chemical characterization of rice husk feedstock and its biochar derivative Some selected chemical properties of the rice husk and its biochar derivative used for the study are presented in the Table 4.2. The pH of the rice husk in water was 6.0 whilst that of its biochar derivative was 8.1. The pH of the rice husk in 1M KCl was 5.2 and that of the rice husk biochar was 8.5. The total carbon content of the rice husk is 400.09 g/kg and after charring increased 1.84 times to 738 g/kg. The total nitrogen content of the rice husk feed stock which was 11.5 g/kg decreased by 57.4% to 4.9 g/kg upon charring. The C:N ratio of rice husk which was 34.8 increased six fold after charring using the Kuntan kiln at temperatures between 537.2 ℃ and 628.1 ℃. Total phosphorus content of the rice husk which was 289 mg/kg increased 20.8 times to 6032 mg/kg when it was converted to biochar. The available phosphorus of the rice husk biochar was 2313 mg/kg. 55 University of Ghana http://ugspace.ug.edu.gh Table 4. 2 Some Chemical properties of the rice husk and its biochar derivative Parameter Rice husk Rice husk biochar pH (water) 6.00 8.10 pH (1M KCl) 5.20 8.50 Total N (g kg-1) 11.50 4.90 Total C (g kg-1) 400.09 738.00 C:N 34.80 150.60 Available P (mg/kg) 2313.00 Total P (mg/kg) 289.00 6032.00 56 University of Ghana http://ugspace.ug.edu.gh 4.3 Characterization of Cow dung The cow dung which was used as a source of organic nitrogen was characterized to know some of its chemical properties and these are presented in Table 4.3. The total nitrogen and total carbon contents of the cow dung were 231 g/kg and 11.8 g/kg, respectively with a C:N ratio of 19.5. 4.4 Soil amendment influence on rice growth parameters This aspect of the results examines the effects of rice husk biochar and different sources of nitrogen on rice growth. The rice growth parameters included weekly plant height, tiller numbers recordings and the dry matter yield which was taken at 42 days after transplanting (DAT). The grain weight at maturity was also taken at 94 DAT. The effect of biochar on weekly plant height is presented on Table 4.4. There was no significant difference in plant height one week after transplanting irrespective of whether the soil was amended with biochar or not as plant height was between 48.5 and 50.7 cm. Two weeks after transplanting the rice plants in the un-amended soils were 62 cm, and significantly 5 cm shorter than those in the biochar amended soils. Three weeks after transplanting the difference in height between the plant from the un-amended soils and the biochar amended ones had increased to 6.4 cm. The differences in height progressively increased to the sixth week where the plants from the un-amended soils attained a height of 95. 5 cm with their biochar amended counterparts being 108.1 cm in height Applying inorganic and organic forms of N fertilizer at different levels resulted in no significant difference in plant height among the various treatments for the various weeks (Table 4.5). The treatments involving inorganic nitrogen fertilizer however recorded higher plant heights compared to the organic nitrogen sources after week 3 (Table 4.5). No lodging was observed for any of the rice plant at any point in time. 57 University of Ghana http://ugspace.ug.edu.gh Table 4. 3 Some chemical properties of cow dung used Parameter Values Carbon (g/kg) 231.00 Nitrogen (g/kg) 11.80 C:N 19.50 Table 4. 4 Effect of biochar application on plant height Biochar rates Wk. 1 Wk.2 Wk. 3 Wk. 4 Wk. 5 Wk.6 B0 48.5 62.0 77.6 87.4 91.3 95.5 B1 50.7 67.0 84.0 95.8. 104.3 108.1 LSD ns 4.9 6.4 7.7 10.8 11.0 Wk: Week Table 4. 5 Different sources and levels of N on weekly rice plant height* N Levels Wk. 1 Wk. 2 Wk. 3 Wk. 4 Wk. 5 Wk. 6 ON0 58.0 68.8 85.8 94.2 98.3 92.0 ON50 45.0 60.4 74.1 83.1 88.6 100.0 ON100 53.0 67.7 83.5 91.2 92.8 97.0 IN50 46.2 65.1 84.3 95.6 102.5 105.0 IN100 44.2 61.3 76.3 94.2 106.8 114.8 LSD ns ns ns ns ns ns ON = Organic N source, IN = inorganic N source, ns=not significant The interaction between different application rates of biochar with different sources and levels of nitrogen resulted in generally no significant difference in the plant height especially from the second week as evident in Table 4.6. 58 University of Ghana http://ugspace.ug.edu.gh As was for plant height, amending soil with biochar at the rate of 50 t/ha, there was no significant difference in tiller numbers compared with the un-amended soil (Table 4.7). Similarly, no significant difference in treatment was observed on weekly basis when different sources and levels of nitrogen were applied on the rice plant. The different levels and sources of nitrogen did not result in significant difference in the weekly tiller number count. However, it was only in the treatment where inorganic N fertilizer was applied at 100 kg/ha that tiller numbers increased progressively with time up to the sixth week after transplanting (Table 4.8) The interaction of biochar with different sources and levels of N did not also result in any significant difference in tiller number as shown in Table 4.9. 4.5 Dry matter and grain yields of rice plant as influenced by soil amendment and application of different nitrogen sources and levels There was significant difference in dry matter yield between treatments of biochar amended and that of the un-amended soils. The dry matter yield of rice was 12.4 g/pot for treatments where the soil was un-amended with biochar and this was significantly different by 29% to 16.06 g/pot when the soil was amended with biochar at 50 tons/ha (p = 0.007 ) (Table 4.10). Similarly, grain yield which was 15.9 g/pot in the un-amended soil increased almost 21% to 19.0 g /pot when the soil was amended with biochar soil (Table 4.10). When no nitrogen was applied, the dry matter yield of rice was 11.86 g/pot which was not significantly different from when organic N was applied at 50 kg N/ha was applied (Table 4.11). 59 University of Ghana http://ugspace.ug.edu.gh Table 4. 6 Effect of biochar-nitrogen interactions on weekly plant height. Treatments Wk.1 Wk.2 Wk.3 Wk.4 Wk.5 Wk.6 B0ON0 64.3 70.0 81.7 88.7 91.7 94.7 B0ON50 42.8 60.2 72.5 80.2 81.8 85.7 B0ON100 49.3 63.0 81.3 91.7 92.7 97.3 B0IN50 43.2 60.2 77.3 87.3 92.0 94.3 B0IN100 42.83 59.0 75.3 89.3 98.3 105 B1ON0 51.7 67.7 90.0 99.7 105.0 106 B1ON50 48.2 62.8 75.7 86.0 105.0 98.3 B1ON100 57.5 72.3 85.7 90.7 93.0 96.7 B1IN50 49.33 70.0 91.3 103.8 113.0 115.7 B1IN100 45.67 63.7 77.3 99.0 115.3 124.0 LSD 7.60 10.82 14.03 18.16 23.06 23.42 Table 4. 7 Influence of biochar on tiller numbers Biochar rates Wk.1 Wk.2 Wk.3 Wk.4 Wk.5 Wk. 6 B0 3.4 7.7 9.4 9.9 10.8 11.0 B1 3.3 7.4 9.2 9.7 11.4 11.8 LSD ns ns ns ns ns ns Table 4. 8 Effects of different sources and levels of N on tiller number N Levels Wk.1 Wk. 2 Wk.3 Wk. 4 Wk.5 Wk. 6 ON0 4.3 7.8 9.5 9.5 10.8 10.8 ON50 3.1 8.0 10.0 10.1 11.5 11.5 ON100 3.6 8.6 10.0 10.0 10.6 10.8 IN50 3.0 7.3 9.5 9.8 11.0 11.0 IN100 3.3 6.0 7.8 9.6 11.8 13.1 LSD ns ns ns ns ns ns 60 University of Ghana http://ugspace.ug.edu.gh Table 4. 9 Influence of biochar nitrogen interactions on tiller number Treatments Wk.1 Wk.2 Wk.3 Wk.4 Wk.5 Wk.6 B0ON0 4.3 8.0 9.0 9.0 11.0 11.0 B0ON50 3.3 7.7 10.7 11.0 11.0 11.0 B0ON100 4.0 8.3 10.3 10.3 10.3 10.3 B0IN50 3.0 7.3 8.7 9.0 10.7 10.7 B0IN100 3.6 7.3 8.7 10.3 11.3 12.3 B1ON0 4.3 7.7 10.0 10.0 10.7 10.7 B1ON50 3.0 8.3 9.3 9.3 12.0 12.0 B1ON100 3.3 9.0 9.7 9.7 11.0 11.3 B1IN50 3.0 7.3 10.3 10.7 11.3 11.3 B1IN100 3.0 4.7 7.0 9.0 12.3 14.0 LSD ns ns ns ns ns ns Table 4. 10 Effects of amending soil with biochar and the influence on dry matter and grain yields Dry matter weight (g/ pot) Grain weight at maturity (g/pot) Biochar rate 42 DAT 94 DAT B0 12.4 15.9 B1 16.0 19.2 LSD 0.9 1.9 Table 4. 11 Nitrogen sources and levels on dry matter and grain yields of rice plant Dry matter weight (g / pot) Grain weight at maturity (g/pot) N Levels 42 DAT 94 DAT ON0 11.86 13.23 ON50 11.45 14.21 ON100 13.67 18.34 IN50 15.77 19.22 IN100 18.41 23.07 LSD 1.43 3.11 61 University of Ghana http://ugspace.ug.edu.gh However, at 100 kg N/ha from cow dung, dry matter increased to 13.67 g/pot. Both inorganic application rates increased dry matter yield significantly to 15.77 and 18.4 g/pot, respectively for 50 kg N/ha and 100 kg N/ha application rates. Dry matter yield was therefore in the order of 0N0 = ON50 < 0N100 < IN50 < IN100 .Grain yield trend was similar to that of the dry matter with the inorganic N sources giving higher yields than their organic counterparts. When both biochar and N at 50 kg/ha from cow dung were amended to the soil, dry matter was 12.47 g/pot which was significantly higher than when the soil was not amended with anything and when the soil was amended with only cow dung N at 50 kg/ha (Table 4.12). On increasing the cow dung N to 100 kg/ha in the biochar amended plot, dry matter increased significantly by 26% to 15.74 g/pot. Amending soil with 50 t/ha biochar and inorganic N at 50 kg/ha increased dry matter significantly to 17.97 g/pot from that of the un-amended soil (10.42 g/pot) and from when only either of the two amendments was applied. The 17.97 g/pot dry matter yield was also significantly higher than yields obtained from the pots from which biochar and cow dung N at the two rates were applied. Amending the soil with biochar and fertilizing with sulphate of ammonia at 100 kg /ha increased dry matter yield from that of the biochar amendment and inorganic N at 100 kg/ha by 20% to 20.06 g/pot. In general the interactive effect of biochar at 50 t/ha and N was in the order of B1IN100 > B1IN50 > B1ON100 > B1ON50. The interactive effects of biochar and N from cow dung at the two rates on grain yield (i.e. comparing treatments B1ON100 and B1ON50) did not show any significant difference between the two rates of N as grain yield was statistically similar with values between 15.6 and 18.4 g/pot. When biochar was however amended with sulphate of ammonia at 50 kg/ha grain yield was 21.4 62 University of Ghana http://ugspace.ug.edu.gh g/pot significantly higher than biochar treatments with the cow dung. On adding 50 kg more sulphate of ammonia, yield increased almost 19% to 25.43 g/pot (Table 4.12). Table 4. 12 The influence of biochar x nitrogen interactions on dry matter and grain yields of rice plant. Dry matter weight at (g /pot) Grain weight at maturity (g/pot) Treatments 42 DAT 94 DAT B0ON0 10.42 11.07 B0ON50 10.63 12.82. B0ON100 11.60 18.25 B0IN50 13.58 17.03 B0IN100 15.76 20.70 B1ON0 13.08 15.40 B1ON50 12.47 18.44 B1ON100 15.74 15.60 B1IN50 17.97 21.40 B1IN100 21.06 25.43 LSD 2.02 4.41 63 University of Ghana http://ugspace.ug.edu.gh 4.6 Effects of biochar on N and P uptake The effect of biochar on uptake of N and P in the plant dry matter is presented in Table 4.13. Uptake of N in rice plants from the un-amended soils averaged 170 mg/pot and this increased 1.3 times to 223 mg/pot when the soil was amended with 50 t/ha biochar. Amending the soil with biochar significantly improved on the P uptake by the rice plants almost 1.5 times from 79 mg/pot in the un-amended soil to 116.5 mg/pot when the soil was amended with biochar (Table 4.13). 4.7 Nitrogen levels and sources on nitrogen uptake When no N was applied to the soil, N uptake was 140 mg/pot which was statistically similar to that when cow dung was applied at 50 kg/ha (157 mg/pot) (Table 4.14). When N from the cow dung was increased to 100 kg/ha, N uptake increased significantly from 157 mg/pot to 201 mg/pot which was statistically similar to the 214 mg/pot uptake from sulphate of ammonia N applied at 50 kg/ha. On increasing Ammonium sulphate N to 100kg N/ha the highest uptake of N at 281 mg/pot was attained. There was significant difference in P uptake when different sources and levels of N were applied. P uptake was lowest when no N source was applied to the rice plant. On amending the soil with cow dung at 50 kg N/ha, P uptake was 81 mg/pot statistically similar to the 77.2 mg/pot observed in the unfertilized soil. Addition of cow dung at 100 kg N/ha increased P uptake significantly to 95.6 mg/pot and further to 107.4 mg/pot when inorganic N at 50 kg/ha was applied. Phosphorus uptake was highest (127.6 mg/pot) when inorganic nitrogen was applied at 100 kg/ha. 64 University of Ghana http://ugspace.ug.edu.gh 4.8 Interactive effect of biochar and nitrogen on N and P uptake Amending soil with biochar and external input of nitrogen fertilizer increased N uptake (Table 4.15). When the soil was amended with biochar at 50 t/ha and cow dung at 50 kgN/ha. N uptake Table 4. 13 Effects of biochar on nutrients uptake Biochar rates N uptake (mg/pot) P uptake (mg/pot) B0 170.0 79.0 B1 223.0 116.50 LSD 26.6 5.86 Table 4. 14 Effects of different sources and levels of nitrogen on plant nutrient uptake N Levels N uptake (mg/pot) P uptake (mg/pot) ON0 140.0 77.2 ON50 157.0 81.0 ON100 201.0 95.6 IN50 214.0 107.4 IN100 281.7 127.6 LSD 42.0 9.2 65 University of Ghana http://ugspace.ug.edu.gh Table 4. 15 Effects of biochar x nitrogen interactions on plant nutrient uptake Treatments N uptake (mg/pot) P uptake (mg/pot) B0ON0 122.0 65.7 B0ON50 160.0 69.1 B0ON100 169.0 74.6 B0IN50 180.0 83.5 B0IN100 247.3 102.2 B1ON0 154.0 92.8 B1ON50 158.0 88.8 B1ON100 230.0 116.6 B1IN50 187.0 131.2 B1IN100 316.0 153.1 LSD 59.0 13.1 (158 mg/pot) statistically similar to when the soil was not amended with neither fertilizer nor biochar. When the N from cow dung was increased to 100 kg/ha N uptake increased almost by 46% to 230 mg/pot. Addition of sulphate of ammonia-N at 50 kg/ha gave similar uptake (187 mg/pot) as when cow dung at 100 kg/ha was applied to the biochar amended soil albeit significantly higher N uptake than the cow dung-N at 50 kg/ha. The interactive effect of biochar and sulphate of ammonia N at 100 kg/ha on rice plant N uptake was significantly the highest with a 29% increase over the same biochar amended soil with sulphate of ammonia-N at 50 kg /ha to 316 mg/pot 66 University of Ghana http://ugspace.ug.edu.gh Amending soil with biochar and cow dung at 50 kg N/ha increased P uptake significantly over that in the un-amended soil (Table 4.15). Plant P uptake from the B1ON50 which was 88.8 mg/pot increased to 116.6 mg/pot when the nitrogen content in the cow dung was increased to 100 kg/ha (B1ON100). On amending the soil with both biochar and sulphate of ammonia N at 50 kg /ha, P uptake by rice plants was 131.2 mg/pot i.e 15 mg/pot more than plants from B1ON100. Further increase of urea-N to 100 kg/ha on the biochar amended soil increased P uptake by the rice plants to 153.1 g/pot (Table 4.15) 4.9 Effects of Amendments on residual soil chemical properties Where soil was amended with biochar at 50 t/ha, the soil residual total nitrogen, total P, total C were significantly higher than where the soil was un- amended with biochar i.e. no biochar was added (Table 4.16). Residual pH which was on the average 4.9 in the un-amended soils increased by 0.5 pH units to 5.4. Biochar amendment increased residual carbon content by 45% from 11.2 to 20.4 g/kg. Total N content almost doubled from 0.32 g/kg to 0.63 g/kg with total P increasing by 64% from 168 g/kg to 275 g/kg. Table 4. 16 Influence of biochar on soil properties (residual soil). Treatments pH Total C (g/kg) Total N(g/kg) Total P(mg/kg) B0 4.9 11.2 0.32 168.0 B1 5.4 20.4 0.63 275.0 LSD 7.0 0.15 49.3 67 University of Ghana http://ugspace.ug.edu.gh 4.9 Influence of nitrogen sources and levels on residual soil chemical properties There were generally no significant difference in pH of the residual soil of the various treatments that received N fertilization from the two sources as residual pH was between 5.0 and 5.3. The unfertilized soil had residual C content of 14.1 g/kg similar to the 13 g/kg before cultivation. On fertilization with cow dung equivalent of 50 kg N/ ha, however, residual C increased significantly to 15.9 g/kg (Table 4.17). Doubling the N from cow dung to 100 kg/ha increased residual C by 17% from that of the un-amended soil to 18.0 g/kg. Inorganic N application from sulphate of ammonia at the two rates gave similar residual carbon levels (15.4 g/kg) as that of ON50. Total N of the soil before cultivation which was 0.8 g/kg (Table 4.1) decreased to 0.33 g/kg after rice cultivation in the unfertilized treatments (Table 4.17). This residual N in the unfertilized soil was not significantly different from N concentrations in soils (0.32 - 0.35 g/kg) that received inorganic N fertilizations. Residual N in the organically N amended soils (0.62 to 0.76 g/kg) were similar to the levels before cultivation but about twice more than their inorganically N fertilized soils. It is worthy of note that apart from the treatments which were fertilized with cow dung at N equivalent of 100 kg/ha and which had residual total P of 323 mg/kg, all the other treatments had statistically similar P contents ranging between 173 mg/kg and 195 mg/kg. 4.10 Effect of biochar and N interaction on Residual soil chemical properties Treatments with biochar but with or without N fertilization had residual pH in water after harvest being similar to the 5.0 before cultivation (Table 4.18). On amendment with biochar at 50 t/ha and inorganically N fertilizing with sulphate of ammonia at both 50 and 100 kg N/ha, residual pH did not vary significantly from that of the soil before cultivation as there was just a marginal increase of between 0.1 unit. However, on amending the soil with biochar and fertilizing with cow 68 University of Ghana http://ugspace.ug.edu.gh dung at the two N rates residual pH was 5.5 in B1ON50 soils and 5.9 for B1ON100 soils. These respective increases of 0.5 and 0.9 pH units above that of the soil before cultivation are significant (Nartey et al., 2000). Residual organic carbon in soils with no biochar but fertilized with either organic or inorganic sources of N were significantly not different from each other with levels of the nutrient between 11.3 and 12.4 g/kg. The organic carbon levels in these soils were however significantly higher than the levels in the un-amended soils (9.4 g/kg) (Table 4.18). Amendment of biochar and N fertilization of the soils increased residual OC contents more than two times with the B1ON100 soil having significantly the highest concentration of 23.5 g/kg. The B1ON50, B1IN50 and B1IN100 had statistically similar OC concentrations of between 19.6 and 20.3 g/kg. It is note-worthy that though biochar- N application interaction was significantly higher in residual N than the soil before amendments, it was only the B1ON100 treatment significantly had higher residual values than in instances where only one of the amendments was applied. There was twice as much residual N in the organically amended plots than their inorganically amended plots at the same rate after harvest. There were no significant differences between the other biochar-nitrogen treatments and treatments that had received either biochar alone or N fertilization alone (Table 4.18). In fact, residual N in the B1ON100 was more than seven times in the soil with no amendment (B0ON0) and 2.1 times more than in B0IN100, and 1.25 times more than before cultivation. There was no clear trend in the residual total P. However, the B1ON100 treatment seem to have accumulated the highest concentration of 367 mg/kg P almost thrice that in the soil before cultivation. 69 University of Ghana http://ugspace.ug.edu.gh Table 4. 17 Influence of N on residual soil chemical properties N Levels pH Total C (g/kg) Total N (g/kg) Total P(mg/kg) ON0 5.1 14.1 0.33 193 ON50 5.0 15.9 0.62 173 ON100 5.3 18.0 0.76 323 IN50 5.1 15.4 0.32 173 IN100 5.1 15.4 0.35 195 LSD 1.22 0.24 Ns Table 4. 18 Influence of biochar nitrogen interactions on residual soil chemical properties Treatments pH Total C (g/kg) Total N (g/kg) Total P(mg/kg) B0ON0 4.9 9.4 0.14 127 B0ON50 4.6 11.7 0.31 150 B0ON100 4.8 12.4 0.52 280 B0IN50 5.1 11.2 0.30 163 B0IN100 5.1 11.3 0.22 120 B1ON0 5.3 18.8 0.53 260 B1ON50 5.5 20.3 0.78 297 B1ON100 5.9 23.5 1.00 367 B1IN50 5.1 19.6 0.35 183 B1IN100 5 19.6 0.48 270 LSD 1.7 0.35 Ns 70 University of Ghana http://ugspace.ug.edu.gh CHAPTER FIVE 5 DISCUSSION 5.1 Characteristics of native soil The soil being clay loam would hold an appreciable amount of water and that may account for its suitability for rice production by the natives. The soil has medium bulk density of 1.34 Mg/m3 due to relatively high amount of silt and clay fractions. The acidic nature (pH of 5.0 in water) could be as a result of the annual ponding of the soil for rice production with concomitant leaching of bases culminating in decrease in pH. This corroborated by the low exchangeable base concentration of 2.83 cmol/kg. This pH is below the average value of 6.5 (Foth and Ellis, 1997) as being ideal for good availability of plant nutrients in mineral soils. The continuous application of sulphate of ammonia as the main N source for rice cultivation in the area could have also contributed to the acidic nature of the soil. Even though the pH of the soil is acidic, inland valley soils are impounded by the rain water most of the time thus creating the lowland condition and this can lead to a shift up of the pH of the flooded soil. The organic carbon content of the soil (13 g/kg) which is unusually higher than the average of northern Ghana soils (Nartey et al., 1997; SRI, 2009) could be as a result of the continuous use of cow dung for rice farming in the area and also the relatively higher moisture content of the soils due to low land rice production that slows down decomposition of organic matter. Despite the total P of the soil being 124 mg/kg, the available phosphorus of the soil is 10.76 mg/kg which is high for soils in Northern Region of Ghana. The use of cow dung by farmers when planting rice might have contributed to the relatively higher Bray available P and total N recorded. Otherwise, these soils in the Northern Region are highly weathered and contain iron and aluminium oxides and oxyhydroxides (sesquioxides) which have the capacity to sorb very large 71 University of Ghana http://ugspace.ug.edu.gh added P or native P thereby transforming them into Fe- and Al-bound forms (Nartey et al., 1997)). The low CEC and hence basic cations of the soil, could be attributed to factors such as the low organic matter and kaolinitic nature of clay as found in similar soils elsewhere in northern Ghana (Nartey et al., 1997). The generally low fertility status of the soil would require for an external input fertilizer to increase the productivity of the soil. 5.2 Characteristics of rice husk and rice husk biochar. The higher biochar pH (8.1) than its feedstock (6.0) is attributed to the chemical cracking of hemicellulose and cellulose during pyrolysis which lead to the release of organic acids and phenolic substances (Struebel et al. (2011); Shinogi and Kanri (2003). These acids react with basic cations in the feedstocks to form alkaline salts which increase the pH of biochar. According to Yuan et al (2011), the increase in pH is due to the formation of ash that contains Ca, Mg, K and Na during the pyrolysis process. During pyrolysis the aliphatic carbon groups in feedstock are condensed into more recalcitrant aromatic carbon leading to a higher concentration per unit weight (Sohi, 2009) and this may account for the 1.84 times more carbon in the biochar than its feedstock from which it was derived. Carbon content of the biochar product increases with increasing temperature (Joseph, 2009). Biochar charring temperatures above 500 °C commonly produce materials with C contents greater than 80 percent. At temperatures between 400 and 500 °C biochars have C contents that range from 60 to 80 percent and biochars produced at low temperatures (< 350 °C) have C content that varies from 15 to 60 percent (Joseph, 2009). In this study, the charring was done at the temperatures of between 537.2 ℃ and 628.1 ℃. It is therefore not surprising that the concentration of carbon was 73.8% with a biochar yield of 57.5% when the ‘Kuntan’ kiln was used for the charring. 72 University of Ghana http://ugspace.ug.edu.gh The total nitrogen content of the rice husk is 11.5 g/kg this is almost double the biochar total nitrogen value of 4.9 g/kg. The 57.4% decrease in nitrogen content of rice husk biochar after charring the feed stock is due to the volatilization of nitrogen during charring process and this is corroborated by Shinogi and Kanri (2003) who found out that about half of N is lost during pyrolysis as temperature increases from 350 to 600 °C. Significant N losses (60-80 percent) have also been reported for biochars produced from rice husks (Bagreev et al., 2001). The higher C:N ratio of biochar than the feedstock is as a result of the carbonization process explained earlier which led to higher biochar carbon content and an attendant decrease in total N relative to the feedstock. Thus, the six-fold increase in C:N ratio of biochar over that of the feedstock is a matter of consequence This high value of C:N ratio of biochar shows that biochar will not easily decompose in the soil and thus would sequester more carbon into the soil to greatly improve carbon stocks of northern Ghana soils should the material be used. Contrary to N, the total P content of the biochar is higher than the P content of the feedstock. Volatilization of P occur at higher temperatures between 700 °C and 800 °C (DeLuca et al., 2009). Since charring was done at temperature below 700 ℃, it is not likely that P was volatilized in this study. The total P content of the biochar was far higher (6032 mg/kg) than that in the feedstock (289 mg/kg) and this is as a result of conversion of organic P to the inorganic form during pyrolysis. The release of the inorganic orthophosphate ions also combines with the liberated Ca to form Ca-P compounds which are not readily soluble and hence increasing significantly the total P contents of the biochar (Lehman, 2007). This in part, may explain why this biochar type has a small available P of 2313 mg/kg. 73 University of Ghana http://ugspace.ug.edu.gh 5.3 Characteristics of Cow dung The total carbon content of cow dung was 231g/kg and total nitrogen content of 12 g/kg generating a C:N ratio of 19.5. With relatively low C:N ratio the cow dung will enable the manure to mineralize easily and supply the soil with high nitrogen content than biochar within a growing season. 5.4 Influence of amendments on Growth parameters Significantly higher weekly plant height was recorded for the biochar amended soils over the non biochar amended ones indicating that just adding biochar at 50 t/ha improved growth of the rice plant as indicated by the increase in plant height. The increased plant height in biochar amended soil over non biochar amended soil is due to the more readily available N in the biochar amended soil as evident in the almost twice more total N in the residual analysis of the biochar amended soil than its un-amended counterpart. The higher available N in the biochar amended soil could have promoted more chlorophyll formation to enhance plant growth as reflected in superior dry matter and grain yield in rice plants from the biochar amended soils. The rice was planted under flooded conditions and therefore the N from the non biochar amended soil could have been leached out faster explaining superior height of rice plants from the biochar amended soils. This is further corroborated by the 1.3 times higher uptake of N by rice plants from the biochar amended soils over the un-amended ones The non-significance in plant height when different levels of N from both cow dung and sulphate of ammonia on height of rice plant confirms that biochar is responsible for increase in plant height of the rice plants. There was no positive influence of biochar alone and in combination with N from the two sources implying that biochar at 50t/ha could not be used in boosting rice yield through tiller formation. 74 University of Ghana http://ugspace.ug.edu.gh 5.5 Influence of amendments on dry matter matter yield The dry matter yield per pot was significantly higher in the biochar amended soils than the un- amended biochar soils due to higher availability of N as explained earlier which is also corroborated by the superior uptake of 1.3 times more N and 1.5 times more P by rice plants from the biochar amended soils with respect to the un-amended soils. Thus, with higher uptake of the two major nutrients N and P, which translated into higher vegetative growth, it stands to reason that rice plants from the biochar amended soils had 29% more dry matter yield than their counterparts. The results are in accordance with Milla et al. (2013) who also found out that applied biochar improved biomass production by increased plant weight. The non-significance in straw dry matter of cow dung-N at 50 kg N/ha could be due to lower content of nitrogen in cow dung for plant uptake compared to relatively higher N content of N applied at 100 kg. With regards to the inorganic N sources at the two rates, there were significant increases in dry matter weight over the un-amended soil could be due to the more readily available N in the latter three N rates. The fact that straw dry matter of rice increased with increasing N amendment especially with the Sulphate of ammonia application and the dry matter was higher in even the inorganic source at 50 kg N/ha than the organic source at 100 kg N/ha confirm the higher availability in the inorganic sources than the organic sources. The result is in accordance with that of Chaturvedi (2005) who reported an increase in dry matter accumulation following increased nitrogen application rates. The organic source would be mineralizing slowly especially under flooded conditions releasing its available N slowly as against the inorganic source which is made up of readily available N. It therefore stands to reason that all the rice plants in the inorganic treatments had higher dry matter contents per pot as N is a major nutrient in chlorophyll formation. This higher availability of N 75 University of Ghana http://ugspace.ug.edu.gh from the inorganic sources than the organic sources is further corroborated by superior N uptake from the inorganic source to the organic sources at the same rate and twice as much residual N in the organically amended plots than their inorganically amended plots at the same rate after harvest. The positive interactive effect of biochar and nitrogen on dry matter yield of rice which did not exist on plant height and tiller numbers indicates that for rice production on the Lima Series with the two amendments dry matter is enhanced more than height and tiller numbers. For increased yield therefore, farmers should rather increase number of seeds per hill if they are planting at stake or increase plant density when they are transplanting. The fact that there was no significant increase in dry matter yield over the un-amended soil when 50 kg N from cow dung was applied to the soil but there was when biochar was added to the same treatment goes to show the positive effect of biochar on rice production. Biochar may have helped in faster N mineralization from cow dung (Milla et al., 2013)). The generally higher dry matter (DM) yields when both biochar and N were applied to Lima series over the un-amended soils and the DM of rice being in the order of B1IN100 > B1IN50 > B1ON50 B1ON100 could be attributed to the increased availability of nitrogen for rice uptake due to enhanced nutrient retention brought about by biochar addition. The high surface area of biochar according to Liang et al. (2006), enhances absorption of NH +4 and NO - 3 thereby reducing leaching losses and offers a mechanism for developing slow release fertilizer which in turn improves nutrient use efficiency and increase the crop yield (Sarkhot et al., 2012). Nitrogen availability in the order of IN100 >IN50 > ON100 > ON50 was enhanced on addition of biochar. 76 University of Ghana http://ugspace.ug.edu.gh 5.6 Influence of amendments on grain yield Nitorgen and P are known to have a major influence in rice grain yield (Purseglov, 1972). With respective 1.3 and 1.5 times more uptake of N and P in rice from the biochar amended soils than their un-amended counterparts, it stands to reason that grain yields in rice grown in the biochar amended soils are 21% more than their counterparts grown in the un-amended soils. Grain yield generally followed the pattern for DM yield and not plant height or tiller numbers. It thus appears that N uptake was translated into dry matter and grain production rather than tiller numbers and plant height. Applying inorganic nitrogen fertilizer led to higher grain yield over the organic nitrogen fertilizer because chemical fertilizer offers nutrients that are readily available and soluble in soil solution to plants. With higher availability of N from the inorganic sources, it is expected that there would be lower residual N. This is evident in the significantly lower residual N in the Lima series to which the inorganic forms of N relative to the non N amended ones (Table 4.17). Nutrient availability from organic sources is due to microbial action (mineralization) which normally takes a longer time hence delay in release of nutrients for plant uptake (Miller, 2007). On the contrary the organically amended soils generally had almost twice as much residual N than their inorganic counterparts at the same application rates and non N amended soils. This has implication for continuous use of the soils. With application of sulphate of ammonia, there still seem to be mining of nutrients from the inherent fertility of the original soil as residual N which was 0.8 g/kg in the soil before cultivation had decreased by about between 56% and 60% to between 0.32 and 0.35 in the inorganically N amended soil. The organically amended soils especially the cow dung applied at 100 kgN/ha seem to be maintaining the fertility of the soil as there was marginal decreases of only 5% and 22.5%, for the cow dung at 50 kgN/ha 77 University of Ghana http://ugspace.ug.edu.gh It is thus clear that the use of inorganic source of nitrogen produced better response to yield than organic source of nitrogen at the expense of maintaining soil fertility. Grain yield increased with increasing rates of nitrogen application. The increase in grain yield in response to application of N fertilizers is probably due to the enhanced availability of nitrogen which enhanced more leaf area resulting in higher photo assimilates and thereby resulted in more dry matter accumulation. These results are supported by the findings of Mandal et al. (1992). Furthermore, increased nitrogen application can lead to increase in the protein percentage, which in turn increased the grain weight (Kausar et al, 1993). The highest grain yield of the harvested rice when biochar was combined with inorganic nitrogen applied at 100 kg/ha over the control and when either of the two amendments was applied alone is consistent with the results of Steiner et al., (2007) and Widowati et al., (2011) who reported an improved crop yield resulting from the application of fertilizer along with biochar due to better N utilization. The reason behind better nutrient utilization was the decrease in N losses due to more NH + 4 adsorption on biochar surfaces (Chan et al., 2008; Masulili et al., 2010). The result is also similar the results of Masulili et al. (2010) who in a pot experiment found that the combined effect of urea and biochar produced more grain yield than the control. Grain yield increase was higher at where biochar was combined with inorganic nitrogen than with the same quantity of organic nitrogen. 5.7 Influence of amendment on nutrient uptake. The amendment of soil with biochar and nitrogen sources resulted in an increased uptake of some soil nutrients. High N uptake of rice at harvest stage was recorded among treatments amended with biochar. The results demonstrated that biochar not only promoted fertilizer N utilization but also enhanced soil N availability to the plant. Biochar can act as a soil conditioner, altering the soil 78 University of Ghana http://ugspace.ug.edu.gh chemical and microbial properties and resulting in an increased uptake of soil nutrients that were not available in otherwise poor soils (Shen et al., 2016; Van Zwieten et al., 2010). The higher uptake of N and P by rice when biochar alone was applied to the soil shows the positive effect of the amendment in making nutrient available. The biochar may have interacted with the native N resulting in faster mineralization with a concomitant release of more available N (Yeboah et al., 2009). The biochar itself contains available P (2313 mg/pot) which may have been made available to the crops and hence the higher uptake in the biochar amended plots Application of inorganic nitrogen resulted in a significantly higher nitrogen uptake by rice than when organic N was applied due to the fact that the inorganic nitrogen source contains more readily available nitrogen compared to the organic nitrogen. The interaction of biochar with nitrogen resulted in a higher nitrogen and P uptake especially when biochar was applied with inorganic nitrogen at 100 kg/ha due to enhanced availability of the two nutrients. Similar results were reported by DeLuca et al. (2009) who stated that biochar added to soil with a nitrogen source yielded an increase in net nitrification and improved the nitrogen availability to the plants. The outcome is also similar to the results of Yeboah et al. (2009) who noted that biochar increased the uptake of nitrogen in plants. The reason for better N content, uptake and N recovery might be the higher nutrient retention capacity of biochar amended soil. The higher intake of both N and P anywhere the two nutrients were applied together could also be due to the synergistic relationship between the two nutrients (Marschner, 1986). Higher availability and uptake of one would lead to higher uptake of the other and vice versa. Phosphorus uptake significantly increased with the application of biochar. Amending soil with biochar resulted in an increased P content of 37 mg/pot over the un-amended soils. The increase 79 University of Ghana http://ugspace.ug.edu.gh in P uptake following amendment with biochar is due to the higher P content of biochar which might have contributed to increase in soil P after amendment and this is supported by by Milla et al., (2013) who reported that addition of nutrient enriched biochar increased the available phosphorus. Similar results were also recorded by Lehmann (2007) who also reported that addition of biochar significantly increased plant growth and nutrition and corroborated by Angst and Sohi (2013) and Yao et al., (2013) who found that biochar adsorbed P more efficiently and became bio- available over a period of time which stimulated plant growth. 5.8 Effects of amendments on residual chemical properties of soil Rice husk biochar has been found to increase pH of Ankasa and Tikobo series, two of the strongly acid soils in Ghana by 1 pH unit after six weeks of incubation (Frimpong Manso, 2017) and the increment has been ascribed to high levels of total and exchangeable Ca and especially Mg in biochar. The 0.5 increase in pH of the biochar amended soils with respective to the un-amended soil after harvest) is significant as a result of the release of basic cations especially the alkali earth metals Ca and Mg found in rice husk biochar (Nartey et al. 2000 ; Frimpong Manso, 2017). The increase in soil pH could also be attributed to the influence of higher pH of 8.1 of rice husk biochar on the soil. Furthermore, Lu et al. (2014) also observed the liming effect in a subtropical paddy soil, which was accentuated by the higher dose of biochar with smaller particle size. There was generally no change in pH of the soils when N from the two sources at the two rates were applied to the soil. Being under flooded condition, nitrification of NH +4 from the two sources were suppressed and hence no change in pH. The interactive effect of biochar and N led to respective 0.6 and 1.0 pH unit increase in the cow dung applied at 50 and 100 kg N /ha mainly due to biochar offering sites for increased mineralization of organic N to NH +4 with a concomitant release of OH - 80 University of Ghana http://ugspace.ug.edu.gh to raise the pH. It therefore stands to reason that residual pH increase was higher in the B1ON100 soil than the B1ON50 counterpart soils because of the higher organic N content of the former. The rice husk biochar has a high C: N ratio of 150.6, it is expected that the carbon will be more stable in the biochar amended soil leading to higher soil carbon levels after cultivation accounting for the higher C contents of 20.4 g/kg compared to the 11.2 of the un-amended soil. Besides, aging of biochar has also been found to increase the carbon content (Sohi et al.,2009). The rice husk biochar amended to the soil at 50 tons/ha contained 4.9 g/kg total N and 6032.0 mg/kg total P and these contents may have contributed to the doubling of residual TN contents and the 64% increase in total P over the contents in the un-amended soil. The carbon contents of the organic nitrogen amended soils recorded higher soil total carbon compared to the inorganic sources of nitrogen with application of organic nitrogen at 100 kg/ha recording the highest residual soil carbon of 1800 mg/kg. This is mainly due the relatively higher carbon content of organic source of nitrogen compared to the inorganic forms. The highest residual organic carbon accumulations in the soil (23.5 g/kg) was found when cow dung at 100 kgN/ha was combined with biochar at 50 tons/ha and this could be due to the contribution of both recalcitrant carbon from biochar and a more labile organic carbon from the cow dung. It is therefore clear that addition of both biochar and cow dung tends to sequester more carbon in Lima soils. There must however be continuous monitoring of the different carbon pools in these soils to ascertain which fraction would enhance soil productivity and how long the carbon content would persist with continuous cultivation. The highest residual N and P in the cow dung amended soil at 100 kg N per ha could be due to the levels in the cow dung and the relatively slow mineralization because of the anaerobic conditions under which the rice was cultivated. This holds promise for subsequent cultivation of the crop 81 University of Ghana http://ugspace.ug.edu.gh since the residual N concentration (0.76 g/kg) in the soil is similar to the level before cultivation (0.8) g/kg whilst there has been an increase in total P levels from 124.5 mg/kg to 323 mg/kg. The interaction of biochar with nitrogen from cow dung applied at 100 kg N/ha resulted in the only significant difference in residual soil total nitrogen among the treatments due to the two amendments possibly increasing CEC of the soil to hold more NH +4 and thereby decreasing leaching. Under flooded conditions, nitrification would be minimized and thus the prevalent form of N in the soil would be NH +4 . With an increase in CEC by the two amendments viz. biochar and cow dung, it stands to reason more ammonium would be retained. With a higher organic N which would not decompose readily, it is a matter of consequence that residual total N and P would be highest in the B1ON100 soil. The highest residual total P in the B1ON100 soil is as a result of the contribution of P from the 50 ton/ha biochar and the cow dung total P applied. 5.9 Nitrogen Use Efficiency (NUE) To assess the effectiveness of the biochar on nitrogen retention, the nitrogen use Efficiency (NUE) was estimated. The Nitrogen Use Efficiency (NUE) was calculated according to the formula by (Baligar, et al., 2007). NUE = 𝑁𝑢𝑡𝑟𝑖𝑒𝑛𝑡 𝑢𝑝𝑡𝑎𝑘𝑒 F(𝑚𝑔)−𝑁𝑢𝑡𝑟𝑖𝑒𝑛𝑡 𝑢𝑝𝑡𝑎𝑘𝑒 𝐶(𝑚𝑔)×100 …………………………………….. [5.1] 𝑄𝑢𝑎𝑛𝑡𝑖𝑡𝑦 𝑜𝑓 𝑛𝑢𝑡𝑟𝑖𝑒𝑛𝑡 𝑎𝑝𝑝𝑙𝑖𝑒𝑑 (𝑚𝑔) Where F = Uptake in soil at specific N application rate and C = Uptake in un-amended soil 82 University of Ghana http://ugspace.ug.edu.gh Table 5. 1 Nitrogen use efficiency of treatments. Treatments NUE% B0ON0 - B0ON50 28.31 B0ON100 20.79 B0IN50 51.32 B0IN100 55.44 B1ON0 - B1ON50 31.85 B1ON100 47.78 B1IN50 57.52 B1IN100 85.84 The NUE shows the ability of the plant to obtain N as a nutrient from the soil (Baligar et al.,2007). In calculating the NUE, the average equivalent N in both organic and inorganic sources of nitrogen were used as the amount of N applied per pot. This translated to 1080 mg per pot for N100 rate and 540 mg N per pot for N50. The NUE of the various fertilized amendments are shown in Table 5.1. The nitrogen use efficiency from the Table 5.1 above shows a higher efficiency in the biochar amended soils than the non biochar amended soils. The highest nitrogen use efficiency (85.84%) was recorded when biochar was amended with Ammonium sulphate N at 100 kg/ha. This represents an increment of 55% over application of ammonium sulphate N at 100 kg/ha without biochar. 83 University of Ghana http://ugspace.ug.edu.gh CHAPTER SIX 6 CONCLUSION AND RECOMMENDATION 6.1 Conclusion The results of the research show that rice husk biochar produced from the rice husk feedstock had a higher pH of 8.1 compared to that of the feedstock of 6.0. The charring of rice husk increased the total carbon content of the biochar to almost about two folds that of the rice husk feedstock. Total P content of the charred material was also higher than that of the feedstock. The results of the experiment also show that there was significant difference in some of the growth parameters of rice when biochar was applied and where no biochar was applied to treatments. Parameters such as plant height, grain weight, straw weight, nutrient uptake, residual soil carbon and nitrogen were influenced by the application of biochar. Rice yield was higher at where soil was amended with biochar as compared to soil un-amended with biochar. Plant height, tiller number, grain yield and nitrogen uptake were positively influenced by the use of inorganic nitrogen fertilizers compared to the organic fertilizers applied at the same rate from different levels. The results also showed positive effects of biochar on nutrient uptake. Uptake of N and P were higher in the biochar amended soils than where no biochar was applied. The biochar amended soils showed increase in total C in the residual soil samples. The residual soil analysis also showed relatively higher total P and total N in the biochar amended soils than soil un-amended with biochar. Results from the residual soil analysis showed that the use of organic nitrogen sources like cow dung will be beneficial in the Northern Region soils because of the high nitrogen and carbon 84 University of Ghana http://ugspace.ug.edu.gh contents of the residual soil implying that rice grown on the same soil in the subsequent season will benefit from the residual soil nitrogen from the organic nitrogen amended soils. Finally the nitrogen use efficiency was higher in the biochar amended soils compared to the non- amended ones 6.2 Recommendations To increase yield of rice in the Northern Region, it is recommended that the nitrogen fertilizer (sulfate of ammonia) be applied together with biochar. The study did not however look at how biochar and nitrogen will influence rice growth in different moisture regimes under lowland conditions especially under the inland valley moisture regime. It is, therefore, recommended that an experiment of this nature be undertaken under field condition to how biochar nitrogen interaction will influence rice growth under different moisture regimes. It is also recommended that another experiment that involve interaction of different rates of organic and inorganic sources of nitrogen with biochar be undertaken in future to observe the growth on yield of rice. Results from the study showed that addition of rice husk biochar prepared from the “Kutan” kiln combined with organic or inorganic nitrogen will contribute to the increase in yield of rice. 85 University of Ghana http://ugspace.ug.edu.gh REFERENCES Abdulai, A. and W. Huffman. (2000). “Structural adjustment and economic efficiency of rice farmers in Northern Ghana”. Economic Development and Cultural Change, 48(3): 503–20. Abdullah, G. Hassan, I.A. Khan, S.A. Khan, S.A. Khan and H. Ali. (2008). 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B 1 0.8333 0.8333 1.09 0.310 N 4 6.6667 1.6667 2.17 0.109 B.N 4 0.6667 0.1667 0.22 0.926 Residual 20 15.3333 0.7667 Total 29 23.5000 Variate: Tiller_No_WK_2 Source of variation d.f. s.s. m.s. v.r. F pr. B 1 0.833 0.833 0.35 0.560 N 4 23.867 5.967 2.52 0.073 B.N 4 11.333 2.833 1.20 0.343 Residual 20 47.333 2.367 Total 29 83.367 Variate: Tiller_No_WK_3 Source of variation d.f. s.s. m.s. v.r. F pr. B 1 0.300 0.300 0.17 0.682 N 4 19.133 4.783 2.76 0.056 B.N 4 12.867 3.217 1.86 0.158 Residual 20 34.667 1.733 Total 29 66.967 Variate: Tiller_No_WK_4 Source of variation d.f. s.s. m.s. v.r. F pr. B 1 0.300 0.300 0.12 0.736 N 4 1.667 0.417 0.16 0.955 B.N 4 12.867 3.217 1.25 0.321 Residual 20 51.333 2.567 Total 29 66.167 113 University of Ghana http://ugspace.ug.edu.gh Variate: Tiller_No_WK_5 Source of variation d.f. s.s. m.s. v.r. F pr. B 1 2.700 2.700 0.59 0.453 N 4 5.667 1.417 0.31 0.869 B.N 4 1.800 0.450 0.10 0.982 Residual 20 92.000 4.600 Total 29 102.167 Variate: Tiller_No_WK_6 Source of variation d.f. s.s. m.s. v.r. F pr. B 1 4.800 4.800 0.77 0.389 N 4 23.467 5.867 0.95 0.458 B.N 4 3.200 0.800 0.13 0.970 Residual 20 124.000 6.200 Total 29 155.467 Variate: Plant_hiegth_WK1 Source of variation d.f. s.s. m.s. v.r. F pr. B 1 29.01 29.01 1.28 0.272 N 4 850.28 212.57 9.36 <.001 B.N 4 423.45 105.86 4.66 0.008 Residual 20 454.00 22.70 Total 29 1756.74 Variate: Plant_hiegth_WK2 Source of variation d.f. s.s. m.s. v.r. F pr. B 1 208.03 208.03 4.86 0.039 N 4 334.25 83.56 1.95 0.141 B.N 4 143.55 35.89 0.84 0.517 Residual 20 855.83 42.79 Total 29 1541.67 Variate: Plant_hiegth_WK_3 Source of variation d.f. s.s. m.s. v.r. F pr. B 1 304.01 304.01 4.31 0.051 N 4 661.03 165.26 2.34 0.090 B.N 4 143.37 35.84 0.51 0.730 Residual 20 1409.83 70.49 Total 29 2518.24 114 University of Ghana http://ugspace.ug.edu.gh Variate: Plant_hiegthWK_4 Source of variation d.f. s.s. m.s. v.r. F pr. B 1 529.2 529.2 5.11 0.035 N 4 610.5 152.6 1.47 0.247 B.N 4 253.4 63.3 0.61 0.659 Residual 20 2071.3 103.6 Total 29 3464.5 Variate: Plant_hiegthWK_5 Source of variation d.f. s.s. m.s. v.r. F pr. B 1 1274.0 1274.0 6.24 0.021 N 4 1281.5 320.4 1.57 0.221 B.N 4 361.2 90.3 0.44 0.776 Residual 20 4081.5 204.1 Total 29 6998.2 Variate: Plant_hiegth_WK_6 Source of variation d.f. s.s. m.s. v.r. F pr. B 1 1190.7 1190.7 5.67 0.027 N 4 1808.0 452.0 2.15 0.112 B.N 4 430.1 107.5 0.51 0.728 Residual 20 4199.3 210.0 Total 29 7628.2 Variate: Grain Weight (grams) at maturity Source of variation d.f. s.s. m.s. v.r. F pr. B 1 80.688 80.688 12.05 0.002 N 4 381.637 95.409 14.24 <.001 B.N 4 21.234 5.308 0.79 0.004 Residual 20 133.967 6.698 Total 29 617.526 Variate: Straw weight at six weeks (grams) Source of variation d.f. s.s. m.s. v.r. F pr. B 1 100.723 100.723 71.21 <.001 N 4 201.369 50.342 35.59 <.001 B.N 4 11.249 2.812 1.99 0.003 Residual 20 28.290 1.414 Total 29 341.631 115 University of Ghana http://ugspace.ug.edu.gh Variate: P uptake Source of variation d.f. s.s. m.s. v.r. F pr. B 1 10543.13 10543.13 177.84 <.001 N 4 10146.19 2536.55 42.79 <.001 B.N 4 1050.07 262.52 4.43 0.02 Residual 20 1185.69 59.28 Total 29 22925.07 Variate: N uptake at………….. Source of variation d.f. s.s. m.s. v.r. F pr. B 1 0.017424 0.017424 14.24 0.001 N 4 0.073257 0.018314 14.97 <.001 B.N 4 0.004480 0.001120 0.92 0.04 Residual 20 0.024470 0.001223 Total 29 0.119631 Variate: Analysis of variance for Residual_soil total_C % Source of variation d.f. s.s. m.s. v.r. F pr. B 1 6.36457 6.36457 617.12 <.001 N 4 0.48144 0.12036 11.67 <.001 B.N 4 0.07856 0.01964 1.90 0.049 Residual 20 0.20627 0.01031 Total 29 7.13084 Variate: Analysis of variance for Residual_soil_total_P % Source of variation d.f. s.s. m.s. v.r. F pr. B 1 86403. 86403. 20.59 <.001 N 4 85133. 21283. 5.07 0.005 B.N 4 18147. 4537. 1.08 0.392 Residual 20 83933. 4197. Total 29 273617. Appendix 2a: Analysis of variance for Residual_soil total_N % Source of variation d.f. s.s. m.s. v.r. F pr. B 1 0.0067410 0.0067410 15.73 <.001 N 4 0.0095065 0.0023766 5.55 0.004 B.N 4 0.0017176 0.0004294 1.00 0.0030 Residual 20 0.0085689 0.0004284 Total 29 0.0265340 116