i
CHARACTERIZATION OF BIOCHAR PREPARED FROM THREE DIFFERENT
FEED STOCKS
A DESSERTATION SUBMITTED TO THE SCHOOL OF GRADUATE STUDIES IN
PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE AWARD OF
MASTER OF AGRICULTURE (SOIL SCIENCE)
BY
GONDAH MOSES ZOLUE
(10360720)
DEPARTMENT OF SOIL SCIENCE
SCHOOL OF AGRICULTURE, UNIVERSITY OF GHANA, LEGON.
JULY, 2013
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DECLARATION
I do hereby declare that this dissertation “CHARACTERIZATION OF BIOCHAR
PREPARED FROM THREE DIFFERENT FEED STOCK” has been written by me and that it is
the record of my own research work. It has neither in whole nor in part been presented for
another degree elsewhere. Works of other researchers have been duly cited by reference to the
authors and all assistance received also acknowledged.
………………………………..
Gondah Moses Zolue
(Student)
……………………………….
Prof. G.N.N. Dowuona
(Principal Supervisor)
……………………………….
Dr. E.K. Nartey
(Co- Supervisor)
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DEDICATION
This thesis is firstly dedicated to God Almighty, and to the indelible memory of my late
parents, Mr. Owen Harris Zolue and Ms. Georgia K. Goneh, who work tirelessly in ensuring that
I had the best of education but never lived to see how far I have come. May your souls rest in
peace. Lastly, I dedicate this work to my Uncle, Jimmy Zolue, who was full of enthusiasm and
total support from the birth of the idea for University’s education. His clever and creative
suggestions provided essential guidance.
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ACKNOWLEDGEMENTS
I firstly want to give thanks to God Almighty for his blessing upon my life and for giving
me strength; knowledge, wisdom and understanding that enable me realize my dream. I wish to
express my sincere gratitude to Prof. G. N. N. Dowuona and Dr. E. K. Nartey for their patience,
guidance, support and encouragement during the course of this work. I must also say I am
grateful to you for reading through my work to enhance its scientific trustworthiness. You will
forever be remembered. I am equally grateful to the Head of Department, Dr. T. A. Adjadeh and
all senior members of the Department of Soil Science for their valuable support.
I wish to express my sincere gratitude to the Government of Liberia through the Ministry
of Agriculture for securing a grant from the African Development Bank to finance my studies at
the University of Ghana. May the glorious land of liberty continue to be ours.
I also wish to express my gratitude to all the laboratory technicians of the Department of
Soil Science especially; Mr. Bernard Anipa, Mr. Julius Nartenor and Mr. Edmund Anum for the
assistance offered me during the period of my laboratory work. I am indeed grateful.
May I also express thanks and appreciation to all my mates; Daniel Ansah Fianko, Brahene
Sebastian Wisdom, Abigail Tettey, Eric Darko, Eric Koomson, Harris Yanquoi, and Emmanuel
Atibila Nsobilafor their good spirit of comradeship.
On a personal note, I wish to thank Zainab Musa Shallangwa, J. Alexander Nyahn Jr., Mr.
Maru Ali and all my colleagues from Liberia for always being there for me. May God give us
long life.
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ABSTRACT
Biochar-based soil management strategies in Ghana are new and are now being evaluated
in the context of the country’s agricultural system. Biochar produced from organic materials
such as saw dust, rice husk and saw dust are being used in Ghana. These different feedstocks
may have different physico-chemical properties which will influence the quality of the biochar
produced when the feedstocks are carbonized and in turn govern their suitability for use in
agriculture. A detailed characterization of biochar produced from rice straw, rice husk and saw
dust was carried out in a bid to document the basic features of the products to ensure their safety
and suitability for use as soil amendments. Rice husk and straw from the same plant material
and saw dust from a saw mill were pyrolysed at 350 oC in a kiln at the Soil Research Institute of
the Council of Science and Industrial Research, Kwadaso, Kumasi. These samples were air
dried and parameters such as particle size distribution, bulk density, available water, electrical
conductivity, pH in water and KCl, total oxidizable organic carbon, total nitrogen, total
phosphorus, available phosphorus, and exchangeable basic cations and total elemental analysis
were carried out. Over 70% of the rice straw and the rice husk biochar types were in the very
small size fraction of between 63 µm and 250 µm. The saw dust biochar, however, had 63.7% of
its size fraction in the coarse size regime of between 500 µm and 2500 µm. The bulk density
values of the three biochar types were very low ranging between 0.19 Mg/m3 and 0.23 Mg/m3.
Moisture content at field capacity was in the order of saw dust (9.55%) > rice straw (8.92%) >
rice husk (7.70%). The rice straw biochar had the highest available moisture content of 3.39%
which was almost 1.7 times higher than that of the saw dust biochar type. The rice straw had the
highest pH of 10.5 as a result of its very high contents total Ca (10.44 mg/kg) and exchangeable
Ca (7.63 cmol/kg) in addition to a high Si concentration of 170.8 mg/kg. The rice straw biochar
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also had the highest EC of 3.57 dS/m due to its high exchangeable Na concentration. The total
oxidisable organic carbon of 191.97 g/kg was highest in the rice straw biochar with the rice husk
sequestering 136.23 g/kg and saw dust 115.8 g/kg. The saw dust biochar type was the lowest in
N content. On account of the C:N ratios of 166.9 for the rice straw, 142 for the rice husk biochar
and 156 for the saw dust biochar, the rice straw biochar type would be the most stable and hence
sequester more carbon. Available P was very high in the rice straw as a result of the high Si
content of the material and was found to be 2.5 and almost 3.8 times more than the total P in the
rice husk and saw dust biochar types, respectively. The concentration of heavy metals Cu, Zn
and more importantly Co and Pb were very low in all the three samples with concentrations
below 0.5 mg/kg due to the near neutral to strongly alkaline pH regime of all the three biochar
types. These very low levels of the heavy metals make the three biochar materials very safe for
use as soil amendments without any toxicity hazards. The study has identified at a charring
temperature of 350 oC, the rice straw biochar has high concentrations of Ca (10.44 mg/kg,) Mg
(1.61mg/kg) and Si (170.8 mg/kg) and a high pH of 10.5 in both water and KCl and therefore has
the potential of being used as an agricultural liming material.
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TABLE OF CONTENTS
PAGE
Title page i
Declaration ii
Dedication iii
Acknowledgements iv
Abstract v
Table of contents vii
List of Tables x
List of Figures xi
1.0 CHAPTER ONE: INTRODUCTION 1
1.1 Background 1
1.2 Justification 4
1.3 Research hypothesis 6
2.0 CHAPTER TWO: LITERATURE REVIEW 7
2.1 Origin of biochar 7
2.2 Biochar 7
2.2.1 Char 9
2.2.2 Charcoal 9
2.2.3 Activated carbon 9
2.2.4 Back carbon 10
2.3 Pyrolysis 10
2.3.1 Slow pyrolysis 12
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2.3.2 Fast pyrolysis 12
2.3.3 Intermediate pyrolysis 13
2.4 Biochar feedstock 14
2.5 Carbonization 15
2.6 Properties of biochar 16
2.6.1 Structural composition 16
2.6.2 Particle size distribution 17
2.6.3 Chemical composition and surface chemistry 18
2.6.4 Pore size distribution and connectivity 21
2.6.5 Cation exchange capacity and pH 22
3.0 CHAPTER THREE: MATERIALS AND METHODS 24
3.1 Sample preparation 24
3.2 Laboratory analyses 24
3.2.1 Particle size distribution 24
3.2.2 Bulk density 24
3.2.3 Available water 25
3.2.4 Electrical conductivity 26
3.2.5 pH in water 26
3.2.6 Total oxidizable carbon 27
3.2.7 Total nitrogen 27
3.2.8 Total phosphorus 28
3.2.9 Available phosphorus 29
3.2.10 Exchangeable cations 29
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3.2.11 Total elemental analysis 30
3.3 Data analysis 30
4.0 CHAPTER FOUR: RESULTS AND DISCUSSION 31
4.1 Physical Properties 31
4.1.1 Particle size distribution 31
4.1.2 Bulk density 32
4.1.3 Moisture content of the biochar 33
4.2 Chemical properties 34
4.2.1 pH 34
4.2.2 Electrical conductivity 36
4.2.3 Total oxidizable carbon 37
4.2.4 Total nitrogen 38
4.2.5 Total and available phosphorus 39
4.2.6 Exchangeable bases 40
4.2.7 Total elemental analysis 40
4.2.8 Suitability for liming 43
5.0 CHAPTER FIVE: SUMMARY AND CONCLUSION 44
5.1 Recommendations 46
6.0 REFERENCES 47
APPENDIX 58
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LIST OF TABLES
TABLES PAGE
2.1 Fate of initial feedstock mass between products of pyrolysis processes 11
4.1 Particle size distributions of the three biochar types 32
4.2 Bulk density of the biochar types 33
4.3 Moisture content of the three biochar types 33
4.4 Some chemical properties of the three biochar types 35
4.5 Exchangeable bases in the three biochar types 41
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LIST OF FIGURES
FIGURES PAGE
4.1 Concentration of the various total elements in the three biochar types 41
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CHAPTER ONE
1.0 INTRODUCTION
1.1 Background
In many tropical environments where rainfall is high, weathering processes over time have
resulted in soils with high amount of iron and aluminum oxides and oxy-hydroxides. Weathering
and leaching have removed basic cations resulting in the formation of acidic soils characterized
by low buffering capacity with potential aluminum release (Fisher and Jakoben, 2000). Such
aluminum (Al) toxicity is one of the most important single factors limiting crop production in
tropical soils (Sanchez, 2000). Acidification which accelerates with deforestation and intensified
cultivation is also having a major impact on the increasing human population in Africa.
Decreasing soil pH increases the instability of soil Al-minerals and thereby increases the
concentration of total Al in soil solution. Speciation of Al depends on pH and a decrease in pH
increases the relative amount of the plant toxic Al3+ ion relative to other Al-species (Matzner et
al., 1998).
The highly weathered soils are mostly dominated by low activity clay minerals such as
kaolinites and sesquioxides (Brady and Weil, 2001). These result in low and declining soil
fertility which arises as a result of continuous cultivation where levels of soil replenishment, by
whatever means, are too low to mitigate the process of soil nutrient mining, in instances where
soil fertility is not restored by new inputs (Shisanya et al., 2009). Consequently, these soils have
poor and declining soil fertility. Increasing cost of mineral fertilizers and its associated
environmental effects, poor quality and low availability of organic amendments pose a serious
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challenge to amending tropical soils. These tropical soils, therefore, remain low in productivity
and require soil amendment.
Amendment of tropical soils in West Africa has been done mainly by the use of fertilizers,
both inorganic and organic. The use of inorganic fertilizers in West Africa is not widespread
because, they are not affordable to a majority of the farmers in the region. Furthermore, due to
high price of imported fertilizers at farm gate and delays in delivery due to poor infrastructure,
smallholder farmers often apply very low rates of inorganic fertilizer late in the growing season,
leading to poor crop-yield responses (Heisey and Mwangi, 1996). Excess applications of
inorganic fertilizers over the years have been one of the major contributing factors to
environmental degradation in Africa (Bationo et al., 2006).
More often than not, the use of inorganic P fertilizer in acidic soils have not had the desired
impact on soil productivity and crop yields because the soluble Al and Fe in and high levels of
sesquioxides and kaolinite which tend to be protonated under those pH regimes sorb the added
inorganic P (Nartey et al., 1997; Abekoe and Tiessen 1998). Thus application of inorganic
fertilizers alone may not help to improve on the productivity of the soils. It has become
imperative for the pH level of the soils to be increased to the desired range for optimum crop
production.
Organic fertilizers though have continued to play an important role in maintaining soil
structure, moisture control, and nutrient levels which gives it an added advantage over inorganic
fertilizers, usage has not been popular under farm conditions because the material cannot supply
all of the nutrients needed to sustain rapid yield growth. Organic matter is also slow in releasing
nutrients to crops. Usage has not also been encouraging because ita application is mostly labour
intensive and requires high application rate. With the high temperatures of the tropics,
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decomposition rate of the material with a concomitant release of CO₂ is fast aggravating global
warming thus leading to a short period for improvement in soil fertility (Sohi et al., 2009).
Organic matter addition buffers and thus though may add nutrients and make P more available
under acidic conditions; it is unable to raise the pH of soils to any appreciable level for optimum
crop production. It is, therefore, not suitable for use as a liming material.
Studies have shown that when organic materials are pyrolysed, the charred material
increases in pH usually above 7 and persists in the soil for a long period of time (Lima et al.,
2002; Lehmann et al., 2003; Glaser et al., 2004; Steiner et al., 2007; Kimetu et al., 2008; Asai et
al., 2009; Gaskin et al., 2008; Major et al., 2010). Spokas and Reicosky (2009) have report that
pyrolysed charred organic material has the potential of increasing soil pH and decreasing
aluminum toxicity. It has, therefore, become important to transform organic matter in to a more
stable form that will persist longer in tropical soils and also help to reduce decomposition rate of
the material and the frequency of application to soils. The remedy to this problem is biochar.
Biochar has been defined as charred organic matter, produced with the intent to
deliberately apply to soils to sequester carbon and improve soil properties (Lehmann and Joseph,
2009). Biochar as a soil conditioner has also been defined as a porous carbonaceous solid
produced by thermo chemical conversion of organic materials in an oxygen depleted atmosphere
with physico-chemical properties suitable for the safe and long-term storage of carbon in the
environment and for soil improvement (Shackley and Sohi, 2010). Biochar is noted to have
numerous characteristics and uses. These include, serving as a soil conditioner by making
nutrients more available to plants and improving soil structure, providing habitat for soil
microorganisms, which in turn may aid in making some nutrients available to crops (Sohi et al.,
2009). The high surface area and pore structure of biochar provides a habitat for soil
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microorganisms, which in turn may aid in making some nutrients available to crops (Lehmann
and Joseph, 2009). Biochar also provides an indirect nutrient effect by reducing leaching of
nutrients that otherwise would not be made available to crops. As a soil enhancer, biochar makes
soil more fertile, boosts food security, preserves cropland diversity, and reduces the need for
some chemical and fertilizer inputs. It improves water quality by helping to retain nutrients and
agrochemicals in soils for use by plants and crops, resulting in less pollution.
Biochar production offers a simple, sustainable tool for managing agricultural wastes. This
can be achieved by converting agricultural waste into a powerful soil enhancer that can preserve
cropland diversity and discourage deforestation. Sustainable biochar can be used now to help
combat global warming by holding carbon in soil and by displacing fossil fuel use (IBI, 2009).
For soils that require liming, there is growing evidence that biochar may provide similar benefits
of improving soil pH balance (Collins, 2008). The quantity of biochar however, that needs to be
applied relative to liming may be high (Yanai et al., 2007). The substitution of biochar for lime
can provide for net carbon benefit compared to standard liming and be cheaper.
Research has shown that the stability of biochar in soil greatly exceeds that of un-charred
organic matter. Biochar retains nitrogen emissions of nitrous oxide hence the potency of the
greenhouse gas may be reduced. Turning agricultural waste into biochar also reduces methane
(another potent greenhouse gas) generated by the natural decomposition of organic matter. To
achieve an advanced process for improving product yields from pyrolysis of selected biomass, it
is important to undertake proper characterization. As such, the physical and chemical properties
of biochar have to be determined so as to fully ascertain the mechanism by which these biochar
produced from different feed stocks can improve upon the productivity of agricultural soils.
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1.2 Justification
In rice growing areas of Ghana, rice husk and straw abound and in almost all regions of
Ghana, there are mountains of saw dust as a result of wood processing from saw mills. These
materials are hardly used as source of organic matter to soils because of their high C:N ratio
(Chan and Xu, 2009). The rice husk and saw dust ‘mountains’ in Ghana breed rodents.
Disposing of these organic materials has been through burning aerobically which cause
environmental pollution. Aerobic burning of organic matter has been noted to account for a 10%
global methane emissions and 1% nitrous oxide emissions (Crutzen and Andreae. 1990).
However, when these organic materials are charred anaerobically, they could serve as valuable
soil conditioners to improve upon the productivity of soils. In Asia, rice husk, rice straw and saw
dust are pyrolysed into biochar and added to improve upon the physical and chemical properties
of soils (Shackley et al., 2011; Sokchea et al., 2012).
Biochar-based soil management strategies in Ghana are new and are now being evaluated
in the context of the country’s agricultural system. According to Sohi et al (2009), to
agronomically use biochar, its properties (physical and chemical) must be measured so as to fully
ascertain the mechanism by which the material is able to improve upon the productivity of
agricultural soils. There is, therefore, a compelling need to determine and understand the
physical and chemical properties of the material.
Biochar produced from organic materials such as saw dust, rice husk and saw dust are
being used in Ghana. These different feedstocks may have different physico-chemical
properties. It is therefore, likely that these different physico-chemical properties will influence
the quality of the biochar produced when the feedstocks are carbonized and may in turn govern
their suitability for use agronomically. It has become imperative to do a detailed characterization
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of biochar produced from rice straw, rice husk and saw dust so as to document their respective
basic features to ensure their safety for use as soil amendments. It is also appropriate to quantify
the key properties that may give rise to the beneficial qualities of biochar from these feedstocks.
The objectives of this study were therefore to:
(a) determine the differences in the physical and chemical properties of biochar produced
from three different feed stocks namely rice straw, rice husk and sawdust.
(b) assess the suitability of rice straw, rice husk and saw dust biochar types as potential
liming materials based on their respective calcium, magnesium and silicon concentration.
1.3 Research hypothesis
HO: There is no difference amongst the physical and chemical properties of biochar produced
from different feedstocks namely; rice straw, rice husk and saw dust
HA: There is difference amongst the physical and chemical properties of biochar produce from
different feedstocks namely; rice straw, rice husk and saw dust.
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CHAPTER TWO
2.0 LITERATURE REVIEW
2.1 Origin of biochar
Biochar was initially linked to the exploration and archaeological study of early human
settlement and soils. These early studies of soils being enriched from what appears to be the
deliberate mixing of burned biomass in soils around human settlements helped spark more recent
interest in biochar. These deposits of enriched soils, known as terra preta in the Amazon region
of South America, have a fascinating history of scientific study of their own (Lehmann et al.,
2003).
More current studies of biochar are focused on its role in a growing demand for biomass-
based energy sources that can mitigate greenhouse gas emissions and slow climate change. In
addition, biochar has the potential to enhance soil quality and soil carbon sequestration. A
secondary source of interest in biochar comes from the growing need to develop low-cost and
healthier biomass-fuelled stove technology.
2.2 Biochar
Biochar is a fine-grained, highly porous charcoal substance that is distinguished from other
charcoals in its intended use as a soil amendment. Biochar is charcoal that has been produced
under conditions that optimize certain characteristics such as high surface area per unit of
volume and low amounts of residual resins deemed useful in agriculture. The particular heat
treatment of organic biomass used to produce biochar contributes to its large surface area and its
characteristic ability to persist in soils with very little biological decay (Lehmann and Rondon,
2006).
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Biochar is produced by the combustion of biomass under oxygen-limited conditions. The
term biochar was originally associated with a specific type of production, known as ‘slow
pyrolysis’. In this type of pyrolysis, oxygen is absent, heating rates are relatively slow, and peak
temperatures relatively low. However, the term biochar has since been extended to products of
short duration pyrolysis at higher temperatures known as ‘fast pyrolysis and novel techniques
such as microwave conversion.
There is a wide variety of char products produced industrially. For applications such as
activated carbon, char may be produced at high temperature, under long heating times and with
controlled supply of oxygen. In contrast, basic techniques for manufacture of charcoal (such as
clay kilns) tend to function at a lower temperature, and reaction does not proceed under tightly
controlled conditions. Traditional charcoal production should be more accurately described as
'carbonization' which involves smothering of biomass with soil prior to ignition or combustion of
biomass whilst wet.
Drying and roasting biomass at even lower temperatures is known as ‘torrefaction’ (Arias
et al., 2008). A charred material is also formed during 'gasification' of biomass, which involves
thermal conversion at very high temperature (800°C) and in the partial presence of oxygen. This
process is designed to maximize the production of synthesis gas (‘syngas’). Materials produced
by torrefaction and gasification differ from biochar in physico-chemical properties, such as
particle pore size and heating value (Sohi et al., 2009) and have industrial applications, such as
production of chemicals (methanol, ammonia, urea) rather than agricultural applications.
In order to differentiate biochar from charcoal formed in natural fire, activated carbon, and
other black carbon materials, it is important to give a clear definition of each since all their
products are obtained from the heating of carbon-rich material.
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2.2.1 Char
This is a solid product arising from thermal decomposition of any natural or synthetic
organic material. Examples are char from forest fire and soot resulting from the incomplete
combustion of fossil hydrocarbon.
2.2.2 Charcoal
Charcoal is produced from the thermal decomposition of wood and related organic
materials and is mainly for use as an urban fuel for heating and cooking. It is also traditionally
used as soil amendment for control of odour (Okimori et al., 2003). Temperatures in traditional
kilns approach 450-500°C, which is similar to that of industrial pyrolysis but with lower yields.
The conversion of feedstock dry mass may be as low as 10% compared to 35% using more
formal production technology. Also, all heat as well as gaseous and liquid co-products are lost
during the combustion process.
2.2.3 Activated carbon
Activated carbon is manufactured by heating carbonaceous material at a high temperature
(above 500°C) and over long (>10 hours) periods of time. The resulting material is characterised
by a very high adsorptive capacity. It is not used as a soil amendment but has been applied for
cleansing processes, such as water filtration and adsorption of gas, liquid or solid contaminants
(Tomaszewski et al., 2007).
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2.2.4 Black carbon
Black carbon: a general term that encompasses diverse and ubiquitous forms of refractory
organic matter that originate from incomplete combustion (Baldock and Smernik 2002). The
diversity of burning conditions results in black carbon occupying a continuum of material.
2.3 Pyrolysis
Pyrolysis is the heating of biomass feedstock under controlled conditions to produce
combustible synthesis gas (‘syngas’), and oil (‘bio-oil’) that can be burnt to produce heat, power,
or combined heat and power. Biochar, the third combustible product produced in pyrolysis, is
the solid charred and carbon-rich residue. Pyrolysis has a requirement for initial energy, in the
same way as in straight combustion. Some heat in the flame is used to initiate combustion of
new feedstock.
The potential advantage of pyrolysis-derived bioenergy over other bioenergy strategies in
terms of greenhouse gas emissions results not only solely from the retention of up to 50% of the
feedstock carbon in stable biochar, but from indirect savings that may result from the use of
biochar in agriculture, specifically the soil (Gaunt and Lehmann 2008). The pyrolysis process
greatly affects the qualities of biochar and its potential value to agriculture in terms of agronomic
performance or in carbon sequestration.
The process and process-parameters, mainly temperature and furnace residence time, are
important in the quality of the product. The process and process conditions, however, also
interact with feedstock type in determining the nature of the product. These variables together
influence the chemical, biological and physical properties, which limit the potential use for
biochar products. Each category of pyrolysis process is characterized by a contrasting balance
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among biochar, bio-oil and syngas as shown in Table 2.1. The precise ratio in these products
may vary between plants, and may be optimized at a particular installation (Demirbas, 2004).
It is critical that maximising the production of biochar relative to mass of initial feedstock
(Demirbas, 2006), is always at the expense of usable energy in the liquid or gaseous form.
Although a greenhouse gas mitigation strategy may favour maximising the biochar product
(Gaunt and Lehmann 2008), the balance that is realised is a function of market and engineering
constraints.
Table 2.1. Fate of initial feedstock mass between products of pyrolysis processes
Process Process Liquid
(bio-oil)
Solid
(biochar)
Gas
(syngas)
FAST PYROLYSIS
Moderate temperature (~500 °C)
Short hot vapour residence time (<2s)
75%
(25% water)
12% 13%
INTERMEDIATE PYROLYSIS
Low-moderate temperature,
Moderate hot vapour residence time
50%
(50% water)
25% 25%
SLOW PYROLYSIS
Low-moderate temperature,
Long residence time
30%
(70% water)
35% 35%
GASIFICATION
high temperature (>800 °C)
Long vapour residence time
5% tar
5% water
10% 85%
Source: (IEA, 2007).
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2.3.1 Slow pyrolysis
Slow pyrolysis can be divided into traditional charcoal making and more modern
processes. It is characterized by slower heating rates, relatively long solid and vapour residence
times and usually a lower temperature than fast pyrolysis, typically 400°C (Bridgwater et al,
1999). The target product is often the char, but this will always be accompanied by liquid and
gas products although these are not always recovered. Slow pyrolysis can also be defined as the
thermal conversion of biomass by slow heating at low to medium temperatures (450 to 650°C) in
the absence of oxygen, with the simultaneous capture of syngas (David et al,. 2006).
Traditional processes, using pits, mounds or kilns, generally involve some direct
combustion of the biomass, usually wood, as heat source in the kiln. Liquid and gas products are
often not collected but escape as smoke with consequent environmental issues (Antal and Grønli,
2003). Feedstock’s in the form of dried biomass pellets or chips of various particle sizes are fed
into a heated furnace and exposed to uniform heating, generally through the use of internal or
external heating as retort furnace or kilns, respectively.
2.3.2 Fast pyrolysis
Fast pyrolysis is characterized by high heating rates and short vapour residence times. This
generally requires a feedstock prepared as small particle sizes and a design that removes the
vapours quickly from the presence of the hot solids. There are a number of different reactor
configurations that can achieve this including ablative systems, fluidized beds, stirred or moving
beds and vacuum pyrolysis systems. A moderate temperature of around 500°C is usually used
(Ensyn, 2009). Very rapid feedstock heating leads to a much greater proportion of bio-oil and
less biochar.
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The time taken to reach peak temperature of the endothermic process (the ‘resistance
time’) is approximately one or two seconds, rather than minutes or hours as is the case with slow
pyrolysis. The lower operating temperature also enhances the overall conversion efficiency of
the process relative to slow pyrolysis. Maintaining a low feedstock moisture content of around
10% and using a fine particle size of < 2mm permits rapid transference of energy despite
relatively moderate peak temperatures of around 450°C (and in the range 350 to 500°C). In
many systems, the transfer is further increased by mechanically enhancing feedstock contact
with the heat source or maximising heat source surface area.
Various technologies have been used and proposed or tested including: fixed beds, augers,
ablative methods, rotating cones, fluidized beds and circulating fluidized beds. Surface charring
must be continuously removed during reaction to prevent pyrolysis of particle interiors being
inhibited by its insulating effect. Bio-oil is condensed from the syngas stream under rapid
cooling, with the combustion of syngas providing the pyrolysis process heat. The bio-oil is a low
grade product with a calorific value, on a volume basis, approximately 55% that of regular diesel
fuel. It is unsuitable as a mainstream liquid transport fuel even after refining, and is most suitable
as a fuel-oil substitute (BEST Energies, 2009).
2.3.3 Intermediate pyrolysis
The term intermediate pyrolysis is used to describe biomass pyrolysis in a certain type of
commercial screw-pyrolyser, the Haloclean reactor (Hornung et al, 2006). This reactor is
designed for waste disposal of electrical and electronic component residues by pyrolysis. When
used for biomass it has performance similar to slow pyrolysis techniques, although somewhat
quicker.
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2.4 Biochar feedstock
Feedstock is the term conventionally used for the type of biomass that is pyrolysed and
turned into biochar. In principle, any organic feedstock can be pyrolysed, although the yield of
solid residue (char) respective to liquid and gas yield varies greatly along with physic-chemical
properties of the resulting biochar.
Feedstock is, along with pyrolysis conditions, the most important factor controlling the
properties of the resulting biochar. Firstly, the chemical and structural composition of the
biomass feedstock relates to the chemical and structural composition of the resulting biochar and,
therefore, is reflected in its behavior, function and fate in soils. Secondly, the extent of the
physical and chemical alterations undergone by the biomass during pyrolysis (e.g. attrition,
cracking, microstructural rearrangements) is dependent on the processing conditions mainly
temperature and residence times (Sjöström, 1993; Demirbas, 2004).
A wide variety of feedstocks can be used depending on location, cost, and availability.
Therefore, the relative proportion of each component will determine the extent to which the
biomass structure is retained during pyrolysis, at any given temperature. The type of feedstock
used for pyrolysis is more important where biochar is to be applied as a soil conditioner (Day et
al., 2005; Das et al., 2008; Gaunt and Lehmann, 2008).
Feedstocks currently used at a commercial-scale or in research facilities include wood chip
and wood pellets, tree bark, crop residues (including straw, nut shells and rice hulls), switch
grass, organic wastes including distillers’ grain, bagasse from the sugarcane industry and olive
waste (Yaman, 2004), chicken litter (Das et al., 2008), dairy manure, sewage sludge (Shinogi et
al., 2002) and paper sludge. The elemental ratios of carbon, oxygen and hydrogen are key
feedstock parameters in commercial use and the quality of fuel products (Friedl et al., 2005).
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The feedstocks which are favoured for bio-oil and fuel-gas are those that have low mineral
and N content. These include wood and biomass from energy crops, including short-rotation
woody plants (such as willow), high productivity grasses (such as Miscanthus sp.), and a range
of other herbaceous plants. They may also include abundant, available and low-cost agricultural
byproducts, including cereal straw.
The proportions of hemi-cellulose, cellulose and lignin content determine the ratios of
volatile carbon (in bio-oil and gas) and stabilized carbon (biochar) in pyrolysis products.
Feedstock’s with high lignin content produce the highest biochar yields when pyrolysed at
moderate temperatures - approximately 500 oC (Demirbas, 2006). Charring of agricultural waste
products such as nut shells and rice hulls for energy production may be advantageous compared
to disposal as waste by some other means (Demirbas, 2006)
2.5 Carbonization
Carbonization is a number of pyrolysis processes that most closely resemble traditional,
basic methods of charcoal manufacture, and which produce biochar of the highest carbon
content. The auto-thermal carbonization process is the small-scale method widely used in rural
communities around the world. The process is optimized for the solid products of pyrolysis, but
condensed gases provide an industrial product known as ‘wood vinegar’, which as well as
providing the basis for food flavouring ingredients, is considered to have a fertilizer value to
plants. The auto-thermal process as the most realistic option has been proposed for the
participation of local communities in using biochar to build soil fertility, especially in developing
countries. It is lower in cost, and easier and simpler than pyrolysis systems where ratios of solid,
liquid and syngas products have to be optimized (Okimori et al., 2003; Ogawa et al., 2006).
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2.6 Properties of Biochar
The combined heterogeneity of the feedstock and the wide range of chemical reactions
which occur during processing, give rise to a biochar product with a unique set of structural and
chemical characteristics (Antal and Gronli, 2003; Demirbas, 2004). According to Sohi et al.,
(2009), it is important that the properties of biochar such as pH, volatile compound content, ash
content, water holding capacity, bulk density, pore volume, and specific surface area measured
so as to have an assessment for the use of the material, agronomically.
2.6.1 Structural composition
Thermal degradation of cellulose between 250 and 350ºC results in considerable mass loss
in the form of volatiles, leaving behind a rigid amorphous C matrix. As the pyrolysis
temperature increases, so does the proportion of aromatic carbon in the biochar, due to the
relative increase in the loss of volatile matter (initially water, followed by hydrocarbons, tarry
vapours, H2, CO and CO2), and the conversion of alkyl and O-alkyl C to aryl C (Baldock and
Smernik, 2002). Around 330 ºC, polyaromatic graphene sheets begin to grow laterally, at the
expense of the amorphous C phase, and eventually coalesce. Above 600 ºC, carbonization
becomes the dominant process. Carbonization is marked by the removal of most remaining non-
C atoms and consequent relative increase of the C content, which can be up to 90% (by weight)
in biochars from woody feedstock’s (Antal and Gronli, 2003; Demirbas, 2004).
Biochar is comprised of stable carbon compounds created when biomass is heated to
temperatures between 300 to 1000°C under low (preferably zero) oxygen concentrations. The
structural and chemical composition of biochar is highly heterogeneous, with the exception of
pH, which is typically > 7. Some properties are pervasive throughout all biochars, including the
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high C content and degree of aromaticity, partially explaining the high levels of biochar’s
inherent recalcitrance. Nevertheless, the exact structural and chemical composition, including
surface chemistry, is dependent on a combination of the feedstock type and the pyrolysis
conditions (mainly temperature) used (Sohi et al., 2009). These same parameters are key in
determining particle size and pore size macro, meso and microspore; distribution in biochar.
Biochar's physical and chemical characteristics may significantly alter key soil physical
properties and processes and are, therefore, important to consider prior to its application to soil.
The physical and chemical properties determine the suitability of each biochar for a given
application, as well as define its behaviour, transport and fate in the environment. Dissimilarities
in properties between different biochar products emphasises the need for a case-by-case
evaluation of each biochar product prior to its incorporation into soil at a specific site. Research
aimed at fully evaluating the extent and implications of particle and pore size distribution of
biochar on soil processes and functioning is essential. The influence on mobility and fate of
biochar is equally important (Gaskin et al., 2008).
2.6.2 Particle size distribution
Initially, particle size distribution in biochar is influenced mainly by the nature of the
biomass feedstock and the pyrolysis conditions (Cetin et al., 2004). Shrinkage and attrition of
the organic material occur during processing, thereby generating a range of particle sizes of the
final product. The intensity of such processes is dependent on the pyrolysis technology (Cetin et
al., 2004). Particle size distribution in biochar also has implications for determining the
suitability of each biochar product for a specific application (Downie et al., 2009), as well as for
the choice of the most adequate application method. In addition, health and safety issues relating
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to handling, storage and transport of biochar are also largely determined by particle size
distribution.
Wood-based feedstocks generate biochars that are coarser and predominantly xylemic in
nature, whereas biochars from crop residues (e.g. rye, or maize) and manures offer a finer and
more brittle structure (Sohi et al., 2009). Downie et al. (2009) have further provided evidence of
the influence of feedstock and processing conditions on particle size distribution in biochar.
Generally, particle size has been found to decrease as the pyrolysis heat treatment
temperature increased (450 -700 ºC range) in saw dust and wood chippings due to a reduction of
the biomass material resistance to attrition during processing (Downie et al., 2009). For higher
heating rates (e.g. 105-500ºC sec-1) and shorter residence times, finer feedstock particles (50-
2000 μm) are required in order to facilitate heat and mass transfer reactions, resulting in finer
biochar material (Cetin et al., 2004). In contrast, slow pyrolysis (heating rates of 5-30ºC min-1)
can use larger feedstock particles, thereby producing coarser biochar (Downieet al., 2009).
Increasing the proportion of larger biochar particles can also be obtained by increasing the
pressure from atmospheric to 5, 10 and 20 bars during processing, which results in both particle
swelling and clustering, due to melting i.e. plastic deformation followed by fusion (Cetin et al.,
2004).
2.6.3 Chemical composition and surface chemistry
Biochar composition is highly heterogeneous, containing both stable and labile
components (Sohi et al., 2009). Carbon, volatile matter, mineral matter (ash) and moisture are
generally regarded as its major constituents (Antal and Gronli, 2003).
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The relative proportion of biochar components determines the chemical and physical
behaviour and function of biochar as a whole (Brown, 2009), which in turn determines its
suitability for a site specific application, as well as transport and fate in the environment
(Downie, 2009). For example, coarser and more resistant biochars are generated by pyrolysis of
wood-based feedstock’s (Winsley, 2007). In contrast, biochars produced from crop residues
(e.g. rye, maize), manures and seaweed are generally finer and less robust (lower mechanical
strength). The latter are also nutrient-rich, and therefore, more readily degradable by microbial
communities in the environment (Sohi et al., 2009).
The ash content of biochar is dependent on the ash content of the biomass feedstock. Grass,
grain husks, straw residues and manures generally produce biochar with high ash contents, in
contrast to that from woody feedstock’s (Demirbas, 2004).
Moisture is another critical component of biochar (Antal and Gronli, 2003), as higher
moisture contents increase the costs of biochar production and transportation for unit of biochar
produced. Keeping the moisture content up to 10% (by weight) appears to be desirable
(Bridgwater and Peacocke, 2000). In order for this to be achieved; pre-drying the biomass
feedstock may be a necessity, which can be a challenge in biochar production.
According to Sohi et al. (2009), the high carbon contents and strong aromatic structure of
biochar largely account for its chemical stability. The pH of biochar shows little variability
among products, and is typically greater than 7. Total carbon content in biochar has been found
to range between 172 - 905 g kg-1, although organic carbon often accounts for <500 g kg-1, as
reviewed by Chan and Xu (2009) for a variety of source materials. Total N varies between 1.8
and 56.4 g kg-1, depending on the feedstock (Chan and Xu, 2009). Despite seemingly high,
biochar total N content, the nutrient may not be necessarily beneficial to crops, since N is mostly
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present in an unavailable form (mineral N contents < 2 mg kg-1; Chan and Xu, 2009). Nuclear
magnetic resonance (NMR) spectroscopy has shown that aromatic and heterocyclic N-containing
structures in biochar occur as a result of biomass heating, converting labile structures into more
recalcitrant forms (Almendros et al., 2003). The C:N ratio in biochar has been found to vary
widely between 7 and 500 (Chan and Xu, 2009), with implications for nutrient retention in soils.
Total P and total K in biochar range broadly according to feedstock, with values between
2.7 - 480 and 1.0 - 58.0 g kg-1, respectively (Chan and Xu, 2009). Interestingly, total ranges of N,
P and K in biochar are wider than those reported in the literature for typical organic fertilizers.
Most minerals within the ash fraction of biochar are thought to occur as discrete associations
independent of the carbon matrix, with the exception of K and Ca (Amonette and Joseph, 2009).
Typically, each mineral association comprises more than one type of mineral ((Amonette and
Joseph, 2009).
The complex and heterogeneous chemical composition of biochars is extended to its
surface chemistry, which in turn explains the way biochar interacts with a wide range of organic
and inorganic compounds in the environment. Aldehyde -(C=O) H, carboxyl -(C=O)OH) and
NO2, occur predominantly on the outer surface of the graphene sheets and surfaces of pores (van
Zwieten et al., 2009). Some of these groups act as electron donors, while others as electron
acceptors, resulting on coexisting areas which properties can range from acidic to basic and from
hydrophilic to hydrophobic (Amonette and Joseph, 2009). Some functional groups also contain
other elements, such as N and S, particularly in biochars from manures, sewage sludge and
rendering wastes.
Different processing conditions (temperature of 700 0C or 450 0C) explained differences in
N contents among three biochars from poultry litter (Lima and Marshall, 2005; Chan et al.,
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2007). As the pyrolysis temperature rises, so does the proportion of aromatic carbon in the
biochar, while N contents peak at around 3000C (Baldock and Smernik, 2002). In contrast, low
processing temperatures (< 5000C) favour the relative accumulation of a large proportion of
available K, Cl (Yu et al., 2005), Si, Mg, P and S (Schnitzer et al., 2007). Therefore, processing
temperatures < 500 oC favour nutrient retention in biochar (Chan and Xu, 2009), while being
equally advantageous in respect to yield (Gaskin et al., 2008). Nevertheless, it is important to
stress that different permutations of those processing conditions, including temperature, may
affect differently each source material. This emphasises the need for a case-by-case assessment
of the chemical and physical properties of biochar prior to its application into soil.
Relating the adverse effect of a particular constituent (or its concentration) of biochar to a
desirable biochar application rate is difficult, as the exact biochar composition is often not
provided in the literature. The review of relevant literature has indicated that the full knowledge
on the composition of biochar as a soil amendment, and the way it is influenced by those
parameters, as well as the implications for soil functioning, is still scarce (Ameloot, et al., 2013).
Partially, this can be explained by the fact that most characterisation work has involved charcoals
with high carbon and low ash content, as required by the increasingly demanding market for
activated carbon. Another factor is the wide variety of processing conditions and feedstock’s
available.
2.6.4 Pore size distribution and connectivity
Biochar pores are classified into three categories (Downie et al., 2009), according to their
internal diameters (ID): macrospores (ID >50 nm), mesopores (2 nm< ID <50 nm) and
micropores (ID <2 nm). These categories are orders of magnitude different to the standard
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categories for pore sizes in soil science. The elementary porosity and structure of the biomass
feedstock is retained in the biochar product formed (Downie et al., 2009). The vascular structure
of the original plant material, for example, is likely to contribute for the occurrence of
macropores in biochar, as demonstrated for activated carbon from coal and wood precursors
(Downie et al., 2009). In contrast, micropores are mainly formed during processing of the parent
material.
Macrospores have been identified as a ‘feeder’ to smaller pores while micropores
effectively account for the characteristically large surface area in charcoals (Brown, 2009). The
development of microporosity in biochar is linked to an increase in structural and organisational
order and is favoured by higher temperatures and retention times, as previously demonstrated for
activated carbon (Lua et al., 2004).
Lua et al. (2004) observed a peak in surface area of pistachio-nut shell char at low heating
rates (10oC), whereas higher heating rates resulted in a decrease in surface area. In particular,
the lignocellulosic composition of the parent material largely determines the rate of its thermal
decomposition, and therefore, the development of porosity (Gonzaléz et al., 2009). In the case of
charcoals from almond tree pruning, a greater volume of meso and macrospores was obtained,
which was accounted for by the slow decomposition rate of such precursor during the initial
stages of pyrolysis (Gonzaléz et al., 2009).
2.6.5 Cation exchange capacity and pH
The CEC variation in biochars ranges from negligible to around 40 cmol kg-1and has been
reported to change following incorporation into soils (Lehmann, 2007). This may occur by a
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process of leaching of hydrophobic compounds from the biochar (Briggs et al., 2005) or by
increasing carboxylation of C via abiotic oxidation (Cheng et al. 2006; Liang et al., 2006).
Considering the very large heterogeneity of its properties, biochar pH values are relatively
homogeneous, that is to say they are largely neutral to basic. Chan and Xu (2009) reviewed
biochar pH values from a wide variety of feedstocks and found a mean of pH 8.1 in a total range
of pH 6.2 – 9.6. The lower end of this range seems to be from green waste and tree bark
feedstocks, with the higher end from poultry litter feedstocks.
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CHAPTER THREE
3.0 MATERIALS AND METHODS
3.1 Sample preparation
Biochar from three feed stock namely, sawdust, rice husk and rice straw were carbonized
at a kiln temperature of 350 oC at the Soil Research Institute of the Council for Scientific and
Industrial Research, Kwadaso, Kumasi. These samples were air dried for about one week and
transported to the Department of Soil Science, University of Ghana for laboratory analyses.
3.2 Laboratory analyses
3.2.1 Particle size distribution
Fifty grams each of the biochar prepared from rice husk, sawdust and rice straw was
weighed into 2.5mm sieves which had been under laid with other sieves of decreasing diameter
of 2mm, 1mm, 0.5 mm, 0.25 mm, 0.125 mm, 0.09 mm and 0.063 mm on a Retsch VS 1000
mechanical shaker. The biochar samples were then shaken continuously at 50 rpm for 5 min.
The various size distributions of each of the three biochar types were then weighed and
expressed as a percentage of the total 50 g mass of biochar taken.
3.2.2 Bulk density
Bulk density was estimated by determining the mass of oven dried biochar that could
occupy a particular volume of container (Jones et al., 2011). A quantity of each of the biochar
types was dried in an oven at 105 0C till a constant mass was attained and kept in a desiccator to
avoid absorption of moisture from the atmosphere. This took about 48 hours. Each of the
samples was poured to fill a 250 cm3 measuring cylinder amidst intermittent gentle tapping to
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ensure good packing to the 250 cm3 mark. The mass of each biochar sample to fill the 250 cm3
volume was then determined by weighing. The bulk density was then calculated from the mass
of biochar divided by the total volume of biochar.
3.2.3 Available water
The moisture content of the three samples was measured at field capacity (1/3 bar or 33
kPa) and at wilting point (15 bar or 1500 kPa) using the pressure plate method (Eilers, 1978).
The biochar samples were placed in the appropriate rings, leveled properly and saturated with
water for 24 hours. After 24 hours, the rings bearing the biochar samples were mounted in the
extractor and the outflow tube connected. The lid was mounted properly and the clamps of the
pressure membrane screwed down. The outflow tube was connected to a 100 mL conical flask
for the collection of water. The pressure in the extractor was turned on with a pressure unit and
maintained at1/3 bar.
After a minute, water from the pressure plate cell started flowing into the conical flask.
The water level in the conical flask or collector was noted for several hours. After 3 days, the
water in the collector stop rising. The same pressure was then maintained for three more days
and it was ensured that there was no further rise of the conical flask water. This then showed
that equilibrium had been attained. The biochar samples were taken out and weighed
immediately. The biochar samples were replaced again in the cell for continuation of the
experiment at different suction value, 15 bar. After a period of five days the samples were taken
out for drying in the oven. The dry weight of the samples and moisture content and different
pressure stages were computed. The difference in moisture content at 33 kPa and 1500 kPa was
estimated as the available moisture content of each biochar sample.
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3.2.4 Electrical conductivity
One gram of biochar from each feedstock i.e. rice straw, rice husk, and saw dust was
weighed into a beaker and 20 mL of distilled water added, to give a biochar water ratio of (1:20).
This ratio was used to ensure enough volume of supernatant for immersion of electrode. The
mixture was then stirred several times for about 30 min and left to stand for about an hour to
allow most of the suspension to settle and also for the suspension temperature to equilibrate with
the temperature in the instrument room.
The electrical conductivity was then determined using the “Solu Bridge” electrical
conductivity meter at cell constant K = 1.06 at 25 0C. The electrode was then rinsed with
distilled water and then immersed into the partly settled suspension and the reading on the
conductivity meter recorded.
3.2.5 pH in water
One gram of biochar (from each feedstock) rice straw, rice husk and saw dust was weighed
into a beaker and 20 mL of distilled water added, to give biochar water ratio of (1:20). 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 left to stand for about an hour to allow most
of the suspension to settle and also for the suspension temperature to equilibrate with the
temperature in the instrument room. The glass electrode pH meter- CG818, Schott Great was
standardized using two solutions of pH 7 and 9. The electrode was then 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.
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3.2.6 Total oxidizable carbon
The oxidizable carbon was determined using the wet oxidation method of Walkley and
Black(1934). This method involves the reduction Cr₂O7
2- ion by the carbon and the unreduced
Cr₂O7
2- measured by titration with ammonium ferrous sulphate.
Hundred milligrams of finely grained sieved biochar (0.5 mm) was weighed in triplicates
into 500 mL Erlenmeyer flask. Ten mL of 1.0 M potassium dichromate (K₂Cr₂O7) followed by
10 mL of concentrated H₂SO4 was added to the biochar. The flask was then swirled making sure
that the solution was in contact with all the particles of the biochar and allowed to stand for about
an hour. Two hundred mL of distilled water was added after which 7 mL of 85%
orthophosphoric acid and few drops of Barium diphenyl-4 sulphonate indicator were added. The
solution was then titrated against 0.5 M acidified ammonium ferrous sulphate solution to a green
end point.
A standardization titration of the K2Cr2O7 with the ferrous ammonium sulphate was done
and the amount of organic carbon calculated by subtracting the number of moles of unreduced
K2Cr2O7 from the number of moles of K2Cr2O7 present in the standardized titration. The
concentration of oxidizable carbon in each of the samples was calculated indirectly from the
number of moles of unreduced dichromate consumed by the ammonium ferrous sulphate.
3.2.7 Total nitrogen
Total nitrogen was determined by a modified Kjeldahl digestion method. The nitrogen in
the sample was converted to ammonium by digestion with concentrated sulphuric acid using
selenium as catalyst and addition of K2SO4 to raise the boiling point of the mixture. The
ammonium formed was determined by distilling the digest with a strong alkali (40% NaOH) and
titration with a standard acid.
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Air dried biochar of 0.2 g was weighed in triplicates into Kjeldahl digestion flasks. The
catalyst and K2SO4 were added followed by 5 mL concentrated H2SO4. The mixture was
digested for about 30 minutes and the digest after cooling, transferred into a 100mL volumetric
flask and made up to volume with deionized water. A 5 mL aliquot was then pipetted into a
Markham distillation apparatus and 5mL of 40% NaOH added and rinsed with deionized water
to about 100 mL. A 5 mL boric acid solution to which few drops of mixed indicator (0.13 g of
methyl red + 0.666 of methylene blue dissolved in 100 mL of 95% ethanol) had been added were
put into a conical flask to trap the liberated ammonia. The distillate was then back titrated with
0.01 M HCl solution. Similar procedure was adopted for a blank which had no biochar sample
to account for traces of N if any, in the reagents and water used. The concentration of N in the
biochar was estimated from the number of moles of HCl consumed in the reaction with
ammonium borate formed when the ammonia was trapped in boric acid.
3.2.8 Total phosphorus
Total phosphorous 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. 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 Murphy and Riley (1962)
method. An aliquot of 5 mL of the sample solution was taken into a 50 mL volumetric flask and
a drop each of P-nitro phenol and 4 M ammonium hydroxide were added until a yellow colour
developed. Then, 8 mL of a solution containing concentrated sulphuric acid, ammonium
molybdate, potassium antimony tartrate, and ascorbic acid were added. The content was topped
up to the 50 mL mark with distilled water. The concentration of phosphorus was then
determined on a Philips’ UV spectrophotometer at a wavelength of 712 nm. The P content of the
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samples in triplicates was then read with the spectrophotometer, with which further calculations
were made using the formula:
P (mg/kg) =
( )
……. [1]
Where SP is sample reading
3.2.9 Available phosphorus
Available phosphorus was determined by the Olsen method (1965). One gram of biochar
sample was weighed into an extraction bottle and 50 mL of sodium bicarbonate solution was
added and shaken for 30 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 Riley method
as described in section 3.2.8. The intensity of the colour at a wavelength of 712 nm was
measured with the spectrophotometer and recorded. The P was calculated using the formula in
Section 3.2.8.
3.2.10 Exchangeable cations
A 2 g biochar was weighed into an extraction bottle and 50 mL of 1 M ammonium
acetate (NH4OAc, pH 7) was added. The bottle was shaken in a mechanical shaker for one hour
and the contents filtered through a Whatman No. 42 filter paper into clean empty bottles.
Exchangeable calcium and magnesium in the extract were determined using the Atomic
Absorption Spectrophotometer (AAS) with exchangeable Na and K being determined by flame
photometry.
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3.2.11 Total elemental analysis
Total elemental analysis of the three biochar samples were done by the wet digestion
method. Fifty milligrams each of the three biochar materials which had been oven dried and
ground was weighed into digestion vessels and wetted with a few drops of de-ionised water.
Five millilitres of concentrated HNO3 and 4 mL of 48% HF and 1.0 mL of HCl were added. The
contents were put on a digestion block and digested slowly amidst intermittent swirling to ensure
complete digestion when the solution became colorless.
Upon complete digestion, the digest was allowed to cool, de-ionised water added and
decanted carefully and made up to volume in a 100 mL volumetric flask, capped and shaken
thoroughly. The total concentration of Si, Fe, Zn, Cu, Pb, Co, Mn, Mg, and Ca levels were
determined on a Perkin Elmer AAS.
3.3 Data Analyses
The various physico-chemical parameters of the biochar determined were subjected to
analysis of variance to determine if differences existed among the three biochar samples.
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CHAPTER FOUR
4.0 RESULTS AND DISCUSSION
4.1 Physical Properties
4.1.1 Particle Size distribution
The particle size distribution of the three biochar samples is presented in Table 4.1. The
smallest size fractions of between 63 and 125 µm was 36.9%, 42.6% and 20.9%, respectively for
the rice straw, rice husk and sawdust biochar types. It is also apparent that 53.8% and 51% of
the size fraction is between 125 and 250 µm for the rice straw and the rice husk biochars,
respectively. The saw dust biochar on the other hand had about 38% of its particles between 125
µm and 250 µm. The largest proportion of 63.7% of the saw dust biochar was in the coarser size
regime of between 500 µm and 2500 µm. In that same coarse size regime of between 500 µm
and 2500 µm, the rice straw and rice husk biochars had only 26.3% and 24.7% size fraction,
respectively. In general, the saw dust can be said to be coarser than its rice counterparts.
Wood-based feedstocks generate biochars which have been found to be coarser and
predominantly xylemic in nature, whereas biochars from crop residues such as cereal have a
finer and more brittle structure (Sohi et al., 2009; Downie et al., 2009). Saw dust is a byproduct
of sawn logs from woody trees with high cellulose, hemicellulose, polyphenol and lignin
contents whereas rice straw and husk are from herbaceous rice plants with lower lignin and
polyphenol contents Attrition during the charring process will hence be higher in the rice based
feedstocks (Cetin et al., 2004). It is therefore, not surprising that the cereal based biochar types
i.e. rice straw and rice husk are finer in texture than their saw dust counterpart.
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The finer nature of rice husk and rice straw than the saw dust biochar has implication for
agriculture. The rice based materials will have larger specific surface area which will result in
more chemical reactive surfaces when amended to soils. The ability to hold and release nutrients
will as a matter of consequence be greater.
Table 4.1. Particle size distributions of the three biochar types.
____________________________________________________________________
Particle Size Rice straw Rice husk Saw dust
(μm) -------------------------------% size distribution--------------------------
____________________________________________________________________
2500 µm 2.7 2.7 4.4
2000 µm 8.3 8.3 12.7
1000 µm 5.0 5.1 5.8
500 µm 10.3 8.6 40.8
250 µm 36.4 27.6 24.9
125 µm 17.4 23.5 13.1
90-63 µm 19.5 19.1 7.8
____________________________________________________________________
4.1.2 Bulk density
The bulk density values of the three biochar types are presented in Table 4.2. The rice
straw biochar type has a statistically lower bulk density value of 0.19 Mg/m3 than the rice husk
and the saw dust. The rice husk and saw dust biochar types have similar bulk density values of
0.22 and 0.23 Mg/m3, respectively. The lower bulk density of the rice straw than the rice husk
could be due to the more fibrous nature of the straw than the husk. The fibrous straw with its
more porous nature would be lighter with a concomitant lower density. In being amended to
soils therefore, the rice straw biochar will be more prone to losses by wind and water.
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Generally all the three materials are very light and therefore as soil amendment, will have
to be incorporated and mixed very well with the soil to avoid losses through water and wind
erosion. Surface application will not be ideal as they will float on water should the soil be
irrigated.
4.1.3 Moisture content of the biochar
The capacities of the three biochar types to hold moisture at 33 kPa and 1500 kPa and their
respective available moisture contents are provided in Table 4.3. At field capacity (FC), there
Table 4.2. Bulk density of the biochar types.
Biochar type Mg/m3
Rice Straw 0.19
Rice Husk 0.22
Saw Dust 0.23
____________________________________________
LSD 0.01
Table 4.3. Moisture content of the three biochar types.
Biochar type FC† (1500 kPa (%) WP‡ (33 kPa) AWC§
-------------------------------(%)---------------------------------------
Rice Straw 8.92b 5.53b 3.39a
Rice Husk 7.70c 5.45b 2.22b
Saw Dust 9.85a 7.86a 1.99b
______________________________________________________________________________
LSD 0.55 0.54 0.25
†FC = field capacity; ‡WP = Wilting point; §AWC = Available water.
Means followed by different letters are significantly different at p = 0.05.
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are clear differences among the three biochar types in the amount of moisture they can hold.
Moisture content at FC is in the order of saw dust (9.85%) >rice straw (8.92%) > rice husk
(7.70%). At wilting point (WP), however, the rice based biochar types had similar moisture
contents of between 5.45% and 5.53% with the saw dust biochar type having the highest
moisture content of 7.86%. Under severe drought conditions, therefore, application of saw dust
biochar to soil should be the preferred choice.
It is worthy of note that despite the superior nature of saw dust biochar in terms of the
volume of moisture it can hold at both FC and WP, it is not the best when availability of
moisture to crops is of prime interest. The rice straw biochar instead, has the highest available
moisture content of 3.39% which is almost 1.7 times higher than that of the saw dust. For water
availability to crops therefore, rice straw ought to be the choice for amendment. Perhaps the
more porous nature of the straw imparts onto the material, the ability to hold more water for
plant usage. From Table 4.3 it is also realized that there is no difference statistically between
saw dust and rice husk in terms of moisture availability.
4.2 Chemical properties
Analytical data on selected chemical properties of the biochar materials are presented in
Table 4.4. Discussion of the individual properties made in the sub-sections below.
4.2.1 pH
The pH of the biochar types in both water (pHw) and KCl (pHKCl) is shown in Table 4.4. In
both media, pH was strongly alkaline with highest value of 10.5 in the rice straw biochar type.
In water, the rice husk biochar had a neutral pH of 6.8 which increased to a slightly alkaline
regime 8.12 in KCl. The saw dust on the other hand, in water recorded a neutral pH of 7.3
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Table 4.4. Some chemical properties of the three biochar types.
Biochar Type EC(dS/cm) pHW pHKCl *AP(mg/kg) †TP(ppm) ‡TN(g/kg) ±TOC(g/kg) C/N
Rice Straw 3.57a 10.50 10.51 1375a 4864a 1.15a 191.97a 166.9
Saw Dust 2.56b 7.31 8.60 89b 363c 0.74c 115.80c 156.0
Rice Husk 0.18c 6.81 8.12 126b 549b 0.96b 136.23b 141.9
____________________________________________________________________________________________________________
LSD 0.034 109.7 12.9 0.05 5.782
Means followed by different letters are significantly different at p = 0.05
*AP = Available Phosphorus
†TP = Total Phosphorus
‡TN = Total Nitrogen
±TOC = Total Organic Carbon
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which changed to a slightly alkaline pH of 8.6 in KCl. The change in pH values, that is ∆pH =
pH KCl –pH H2O are positive 1.29 and 1.31, respectively for the saw dust biochar and rice husk
biochar. The positive ∆pH of the saw dust and rice husk biochar types is an indication that as
variable charged materials, the two have net positive charges (Evangelou, 1998). Thus the anion
exchange capacities of saw dust and rice husk biochar are likely to be higher than that of the rice
straw biochar type. Adsorption of anions such as nitrates, phosphates and sulphates
nonspecifically, for later release to crops may be enhanced should the two materials be added to
highly weathered and sandy soils. The neutral pH of the two materials is an added advantage as
they are likely to make P one of the most limiting nutrients in tropical soils more available. The
rice husk and the saw dust biochar types with their net positive charges could also be used as
chemical filters to remove anionic contaminants from the environment. Incorporation of these
two materials to soil could minimize leaching of nitrates with a decrease in groundwater
pollution.
4.2.2 Electrical conductivity
The electrical conductivity (EC) values of the three biochar types follow similar trends as
the pH. The rice straw biochar has the highest EC value of 3.57 dS/m with the saw dust biochar
being 2.56 ds/m and the rice husk biochar the lowest EC of 0.18 dS/m. From the EC values, it is
clear that all the materials are not saline. However, the rice straw biochar which has the highest
EC of 3.57 dS/m and pH of 10.5 is approaching the critical limit of 4 dS/m for salinity
(Evangelou, 1998). It is therefore, advisable for this material not to be used in soils with
moderate to high sodium content as it may lead to salinization of the soils. Caution must be
exercised in using the rice straw biochar on near to neutral soils as frequent application may lead
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to salinity build up. The saw dust and rice husk biochar types could be used on near to neutral
soil with the rice straw biochar being used as amendment of acidic soils where solubility of Na
and salinity are not likely to be high.
4.2.3 Total oxidizable organic carbon
The total oxidisable organic carbon of the three materials as shown in Table 4.4 is in the
order of rice straw > rice husk > saw dust. The 191.97 g/kg, 136.23 g/kg and 115.8 g/kg,
respectively for the rice straw, rice husk and saw dust biochar is in consonance with organic
carbon contents obtained by Chan and Xu (2008) for a variety of biochar materials.
The proportions of hemi-cellulose, cellulose and lignin content determine the ratios of
volatile carbon (in bio-oil and gas) and stabilized carbon (biochar) in pyrolysed products.
Feedstocks with high lignin content produce the highest biochar yields when pyrolysed at
moderate temperatures, approximately 500 °C (Fushimi et al., 2003; Demirbas, 2006). It was,
expected that the saw dust biochar which came from woody plant species and is more lignified
would have the highest organic carbon content. The higher significant levels of organic carbon
in the two rice biochar types than their saw dust counterpart could be as a result of the lower kiln
temperature of 350 oC used in the carbonization process for the three materials.
Thermal degradation of cellulose between 250 and 350 ºC results in considerable mass loss
in the form of volatiles, leaving behind a rigid amorphous C matrix. As the pyrolysis
temperature increases, so does the proportion of aromatic carbon in the biochar, due to the
relative increase in the loss of volatile matter (initially water, followed by hydrocarbons, tarry
vapours, H2, CO and CO2), and the conversion of alkyl and O-alkyl C to aryl C (Baldock and
Smernik, 2002). Above 600 ºC, carbonization becomes the dominant process. Carbonization is
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marked by the removal of most remaining non-C atoms and consequent relative increase of the C
content, which can be up to 90% (by weight) in biochars from woody feedstock’s (Antal and
Gronli, 2003; Demirbas, 2004). It, therefore, stands to reason that the rice straw and the rice
husk biochar types have higher organic carbon contents than the saw dust type as they are less
lignified and hence must have lost most of their respective non-carbon contents with a
concomitant increase in carbonisation by the 350 oC kiln temperature employed.
The rice straw biochar being highest in oxidizable carbon implies that it should be the
preferred material among the three for carbon sequestration at a charring temperature of 350 oC.
This is because the rice straw biochar would convert a lot more atmospheric carbon into a more
stable form of carbon than the rice husk and saw dust biochar types.
4.2.4 Total nitrogen
The total nitrogen contents of the three biochar types were 1.15 g/kg, 0.96 g/kg and 0.74
g/kg for rice straw, rice husk and saw dust, respectively. Statistically, the saw dust biochar type
was the lowest in N content and this agrees with findings of Fushimi et al. (2003) and Demirbas
(2006) who noted that biochar types from woody plant species have low N contents.
The relatively higher total nitrogen value observed for rice straw and rice husk compared
to saw dust biochar type might be due to the more plant uptake of N from application of
nitrogenous fertilizers which is common in rice cultivation. The higher total N in the rice straw
biochar than the rice husk biochar is a confirmation of the fact that more N is needed for
vegetative growth than seed formation.
The C:N ratios of the three biochar types as presented in Table 4.4 are 166.9 for the rice
straw, 142 for the rice husk biochar and 156 for the saw dust biochar. On application to soils, the
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rice straw biochar type would have the highest stability and hence sequester more carbon
because degradation would be slowest. The rice husk biochar type at a charring temperature of
350 oC would have the highest degradability and hence the least stable on application to soils.
4.2.5 Total and available phosphorus
The total phosphorus (TP) concentration of the e three biochar shows that rice straw
biochar had the highest TP accumulation of 4864 mg/kg with the rice husk biochar accumulating
only 549 mg/kg TP. The lowest TP content of 363 mg/kg was observed in the saw dust biochar.
Even though the straw and husk came from the same rice plant, the straw biochar has strikingly a
higher TP content which is almost 9 times more than the TP in rice husk biochar. Phosphorus is
utilized by cereals in the strengthening of structural tissues, particularly straws (Brady and Weil,
2002). It is therefore, not surprising that the rice husk biochar has the highest accumulation of
TP. The exceptionally high TP in the rice straw biochar type could also be in indication that the
rice plant from which the material was harvested may have received heavy dose of P application.
Available P concentration in the three biochar types also followed a similar pattern as total
P with the rice straw having the highest available P content of 1375 mg/kg. In fact this available
P level in the rice straw which is 28.26% of the total P is 2.5 and almost 3.8 times more than the
total P in the rice husk and saw dust biochar types, respectively. The high available P contents of
the rice husk biochar are as a result of its high TP.
Most tropical soils are highly weathered and dominated by sesquioxides and kaolinite.
Consequently P availability is low. Addition of rice straw biochar with its high pH high organic
carbon, TP and available P contents, especially to acidic tropical soils holds promise for P
availability. The high pH will reduce the acidity and with the high organic carbon, high total and
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available P, P availability could be enhanced. It may be interesting to conduct an experiment to
ascertain the combined effect of application of rice straw biochar and inorganic P fertilizers on
productivity of highly weathered acidic P deficient soils.
4.2.6 Exchangeable bases
The concentration of the exchangeable bases Ca, Mg, K and Na in the three biochar types
are presented in Table 4.5. The highest exchangeable Ca and Mg levels of 7.63 cmol/kg and
1.73 cmol/kg, respectively was observed in the rice straw biochar. These high levels of the two
exchangeable cations may account for the strikingly high pH of the material. The sum of Ca and
Mg in the saw dust biochar (1.91 cmol/kg) was higher than that of rice husk biochar (1.22
cmol/kg) explaining the higher pH of the saw dust than the rice husk biochar.
The Na levels were exceptionally high in the rice straw (30 cmol/kg), more than 16.6 times
and 22.7 times the levels found in the rice husk and saw dust biochar types, respectively. The
very high level of exchangeable Na in the rice straw accounts for its high EC of 3.56 dS/m. The
higher exchangeable Na in the saw dust biochar than the rice husk biochar is also in consonance
with its higher EC. In general, the sum of bases was highest in the rice straw followed by the
saw dust biochar with the lowest sum of bases in the rice husk biochar and this trend ties in well
with the pH values of the three biochar materials.
4.2.7 Total elemental analysis
The total Ca, Mg, Fe, Zn, Cu, Pb, Co and Si concentrations in the three biochar types are
shown in Figure 4.1. From the figure, it is clear that the concentration of total basic cations (Ca
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Table 4.5. Exchangeable bases in the three biochar types.
Biochar Type Ca Mg K Na Sum of Bases
---------------------------------------------------cmol/kg----------------------------------------------------
Rice Straw 7.63a 1.73a 1.48a 30a 40.84
Rice Husk 0.36c 0.86b 0.78c 1.32c. 3.32
Saw Dust 1.23b 0.68b 1.13b 1.81b 4.85
__________________________________________________________________________
LSD 0.15 0.66 0.06 0.12
Figure 4.1. Concentration of the various total elements in the three biochar types.
and Mg ) are highest in the rice straw with Ca being highest with a content of 10.4 mg/kg. The
Ca content in the straw is more than twice that found in the saw dust and more than thrice the
content in the rice husk biochar. The high Ca and Mg contents of the rice straw biochar also
explain the high exchangeable forms of the cations in the material (Table 4.4).
0.00
0.20
0.40
0.60
0.80
1.00
1.20
1.40
1.60
1.80
Ca(× 10) Mg Pb Fe Mn Zn Co Cu Si(× 102)
co
n
ce
n
tr
at
io
n
(
m
g/
kg
)
Elements
RICE STRAW SAW DUST RICE HUSK
a
b
c
a
b
c
a
b
c
a
b b
a
c
b
a
b
c
a
c
b
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The high levels of total basic cations, particularly Ca may, in part, account for the very
high pH of 10.5 in both water and KCl observed for the rice straw biochar. The high total Ca
and Mg content of the rice straw biochar coupled with its high pH makes the material a good
choice for use as a liming material. The high level of Ca may exchange for Al at the exchange
site of acid soils thereby decreasing exchangeable acidity.
The concentration of heavy metals Cu, Zn and particularly Co and Pb are very low in all
the three samples with concentrations below 0.5 mg/kg. These very low levels of the heavy
metals make the three biochar materials very safe for use as soil amendments without any
toxicity hazards. The biochar materials all have pHs between 6.8 and 10.5. These neutral to
strongly alkaline pH may explain the trace to very low levels of heavy metals in the biochar
materials.
The Fe concentration in the saw dust biochar of 1.23 mg/kg was the highest with the rice
straw having the lowest concentration of 0.14 mg/kg. The very low level of Fe in the rice straw
biochar is as a result of its high alkaline pH. Iron is an acidic cation and hence will not
predominate in alkaline medium.
The silicon concentration of the biochar materials were in the order of rice straw biochar >
rice husk > saw dust. Just as was observed for Ca, the rice straw had the highest Si content of
170. 8 mg/kg Si which is 63 mg/kg and 76 mg/kg higher than the contents in the rice husk and
saw dust biochar types. Silicon is a nutrient in rice production and this explains the relatively
higher levels of the rice biochar types than their saw dust counterpart. The higher Si content of
the rice straw may be due to the nutrient being absorbed by the rice plant in addition to Ca and P
for strengthening of the skeletal stem tissue (Purseglov, 1972).
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The pK1 of silicic acid (H4SiO4) is between 9.6 and 9.8 (Nartey et al., 2000). This pK
value is just 0.7 pH units lower than the pH of the rice straw biochar. A large proportion of Si in
the rice straw biochar when applied to the soil may therefore be in the conjugate base form,
H3SiO4
-. This species of Si in addition to the acid, H4SiO4 have higher abilities to be adsorbed
onto surfaces of sesquioxides and kaolinite than the available plant forms of P, H2PO4
- and
HPO4
2- (Tisdale et al., 2002) Addition of rice straw to highly weathered tropical soil may
therefore enhance P availability. The presence of the H4SiO4 and its conjugate base H3SiO4
- in
the rice straw which has a high TP content of 4864 mg/kg may account for the very high
available P content of 1375 mg/kg.
4.3 Suitability for liming
An agricultural liming material has been defined as any substance that can supply Ca and
Mg as cations in combination with carbonates, hydroxyls, oxides and silicates as anions (Brady
and Weil, 2002). From the total analyses, it is seen that the rice straw biochar has the highest
concentrations of Ca (10.44 mg/kg,) Mg (1.61mg/kg) and Si (170.8 mg/kg). The material also
has a high pH of 10.5 in both water and KCl. It is, therefore clear that the rice straw is a suitable
biochar for use as an agricultural liming material. Considering the readily availability of rice
straw and some cheap improvised local methods of biochar production being employed, the use
of rice straw biochar may be the panacea to the acidic problems of highly weathered tropical
soils. Experiments will, however, have to be conducted to calculate the CaCO3 equivalent of the
rice straw biochar. This is to help estimate the amount of the material to apply and evaluate its
competitiveness in terms of cost in comparison with the traditional liming materials.
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CHAPTER FIVE
5.0 CONCLUSIONS AND RECOMMENDATION
The work has shown that there are differences in the physical and chemical properties
when rice husk, rice straw and saw dust are pyrolysed at a temperature of 350 oC. It is apparent
from the study that over 70% of the rice straw and the rice husk biochars were in the very small
size fraction of between 63 µm and 250 µm. The saw dust biochar on the hand had the
proportion of 63.7% of the material in the coarse size regime of between 500 µm and 2500 µm.
The bulk density values of the three biochar types were very low ranging between 0.19
Mg/m3 and 0.23 Mg/m3. Generally all the three materials are very light and therefore as soil
amendment, will have to be incorporated and mixed very well with the soil to avoid losses
through water and wind erosion. Surface application will not be ideal as they will float on water
should the soil be irrigated.
Moisture content at field capacitywas in the order of saw dust (9.55%) > rice straw (8.92%)
> rice husk (7.70%). At wilting point (WP), however, the rice based biochar types had similar
moisture contents of between 5.45% and 5.53% with the saw dust biochar type having the
highest moisture content of 7.86%. Under severe drought conditions, therefore, application of
saw dust biochar to soil should be the preferred choice. The rice straw biochar had the highest
available moisture content of 3.39% which was almost 1.7 times higher than that of the saw dust
making rice straw the preferred choice of material in terms of water availability to crops.
There were significant differences in pH among the three biochar types with the rice
straw recording the highest value of 10.5 in both water and KCl as a result of its very high
contents total Ca of 10.44 mg/kg and exchangeable Ca of 7.63 cmol/kg in addition to a high Si
concentration of 170.8 mg/kg. The saw dust had a pH of 8.12 in water with the rice husk
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recording a neutral pH of 6.8 in water. The change in pH values, that is ∆pH = pH KCl –pH H2O
were positive for the rice husk and saw dust biochar types indicating that the two materials could
be used as sorbents for anions. The rice straw biochar also had the highest EC value of 3.57
dS/m due to its high exchangeable Na concentration.
The total oxidisable organic carbon of 191.97 g/kg was highest in the rice straw biochar
with the rice husk sequestering 136.23 g/kg and saw dust 115.8 g/kg at a kiln temperature of 350
oC. The saw dust biochar type was the lowest in N content. On account of the C:N ratios of
166.9 for the rice straw, 142 for the rice husk biochar and 156 for the saw dust biochar the rice
straw biochar type would be the most stable and hence sequester more carbon.
Total and available P were particularly high in the rice straw biochar with the material
accumulating respective levels of 4864 mg/kg and 1375 mg/kg. The high available P in the rice
straw which was as a result of the high Si content of the material was found to be 2.5 and almost
3.8 times more than the total P in the rice husk and saw dust biochar types, respectively.
The concentration of heavy metals Cu, Zn and particularly Co and Pb are very low in all
the three samples with concentrations below 0.5 mg/kg due to the near neutral to strongly
alkaline pH regime of all the three biochar types. These very low levels of the heavy metals
make the three biochar materials very safe for use as soil amendments without any toxicity
hazards.
The study showed that the rice straw biochar has the highest concentrations of Ca (10.44
mg/kg,) Mg (1.61 mg/kg) and Si (170.8 mg/kg). The material also has a high pH of 10.5 in both
water and KCl and therefore has the potential of being used as an agricultural liming material.
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5.1 Recommendations
It is recommended that further studies be carried out in the laboratory to determine the
CaCO3 equivalence of the rice straw biochar. This is to help estimate the amount of the material
to apply and evaluate its competitiveness in terms of cost in comparison with the traditional
liming materials. The study should also be extended to the field thereafter to ascertain the
efficacy of the rice straw biochar type as a liming material and also its effect on soil productivity
by evaluating the growth and yield of an added test crop.
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REFERENCES
Abekoe, M.K. and Tiessen, H. (1998). FertilizerP transformations and P availability in hillslope
soils of Northern Ghana. Nutrient Cycling in Agroecosystems, 52: 45-54.
Almendros, G., Knicker, H., Gonzaléz-Vila, F. J. ( 2003). Rearrangement of carbon and nitrogen
forms in peat after progressive thermal oxidation as determined by solid-state 13C- and
15N-NMR spectroscopy. Organic Geochemistry, 34: 1559-1568.
Ameloot, N., Graber, E. R., Verheijen, F. G. A. and De Neve, S. (2013). Interactions between
biochar stability and soil organisms: review and research needs. European Journal of Soil
Science, 64: 379–390.
Amonette, J.E., Jospeh, S. (2009). Charecteristics of biochar: Microchemical properties. In: J.
Lehmann, Joseph, S. (Editors), Biochar for Environmental Management Science and
Technology. Earthscan, London.
Anon, 2008. Gasification: redefining clean energy. In: Gasification Technologies Council,
Arlington, VA, pp. 25.
Antal, M.J., Grønli, M. (2003). The art, science and technology of charcoal production.
Industrial and Engineering Chemistry Research, 42: 1619-1640.
Arias, B., Pevida, C., Fermoso, J., Plaza, M.G., Rubiera, F., Pis, J.J. (2008). Influence of
torrefaction on the grindability and reactivity of woody biomass. Fuel Processing
Technology, 89: 169-175.
Asai, H., Samson, B. K., Stephan, H. M., Songyikhangsuthor, K., Homma, K., Kiyono, Y., Inoue
Y., Shiraiwa, T. and Horie, T. (2009). Biochar amendment techniques for upland rice
production in Northern Laos: 1. Soil physical properties, leaf SPAD and grain yield. Field
Crops Research 111, 81-84pp.
University of Ghana http://ugspace.ug.edu.gh
48
Baldock, J.A., Smernik, R. J. (2002). Chemical composition and bioavailability of thermally
altered Pinusresinosa (red pine) wood. Organic Geochemistry, 33: 1093-1109.
Bationo, A., Hartemink, A., Lungu, O., Naimi, M., Okoth, P., Smaling, E. and Thiombiano, L.
(2006). African soils: their productivity and profitability of fertilizer use. In: Proceedings
of the African Fertilizer Summit, June 9–13, 2006, Abuja, Nigeria. 29pp.
BEST Energies Inc. (2009). BEST Energies web site BEST Energies Inc., Wisconsin,
USA.http://www.bestenergies.com/companies/bestpyrolysis.html 12.08.09.
Brady, N.C. and Weil, R.R. (2001). The Nature and Properties of Soils. 11th Edition. Prentice
Hall, New Jersey.
Brady, N.C. and Weil, R.R. (2002). The Nature and Properties of Soils. 12th Edition. Prentice
Hall, New Jersey.
Bridgwater, A.V. and Peacocke, G.V.C. (2000). Fast Pyrolysis Processes for Biomass.
Renewable and Sustainable Energy Reviews, 4: 1-73.
Bridgwater, A.V., Meier, D. And Radlein, D. (1999). An overview of fast pyrolysis of biomass.
Organic Geochemistry, 30: 1479-1493.
Briggs, C.M., Breiner, J., and Graham, R.C., (2005). Contributions of Pinus Ponderosa Charcoal
to Soil Chemical and Physical Properties. The ASA-CSSA-SSSA International Annual
Meetings (November 6-10, 2005), Salt Lake City, U.S.A.
Brown, R. (2009). Biochar Production Technology. In: J. Lehmann, Joseph, S. (Editors),
Biochar for Environmental Management Science and Technology. Earthscan, London.
Cetin, E., Moghtaderi, B., Gupta, R. and Wall, T. F. (2004). Influence of pyrolysis conditions on
the structure and gasification reactivity of biomass chars. Fuel, 83: 2139-2150.
University of Ghana http://ugspace.ug.edu.gh
49
Chan, K.Y., van Zwieten, B.L., Meszaros, I., Downie, D., & Joseph, S. (2007). Agronomic
values of greenwaste biochars as a soil amendments. Australian Journal of Soil Research,
45, 437–444.
Chan, K. Y. and Xu, Z. (2009). Biochar: Nutrient Properties and Their Enhancement. In: J.
Lehmann, Joseph, S. (Editors), Biochar for Environmental Management Science and
Technology. Earthscan, London.
Cheng, C-H, Lehmann, J., Thies, J., Burton, S. D. and Engelhard, M. H. (2006). Oxidation of
black carbon by biotic and abiotic processes. Organic Geochemistry 37: 1477-1488.
Chen, J., Zhu, D. and Sun, C. (2007). Effect of heavy metals on the sorption of hydrophobic
organic compounds to wood charcoal. Environmental Science and Technology,41: 2536-
2541.
Collins, H. (2008). Use of biochar from the pyrolysis of waste organic material as a soil
amendment: Laboratory and greenhouse analyses. From a quarterly progress report
prepared for the Biochar Project. December 2008.
Crutzen, P. J. and Andreae, M. O. (1990). Biomass burning in the tropics: Impact on
atmospheric chemistry and biogeochemical cycles. Science, 250: 1669-1678.
Das, K.C., Garcia-Perez, M., Bibens, B and Melear, N. (2008). Slow pyrolysis of poultry litter
and pine woody biomass: Impact of chars and bio-oils on microbial growth. Journal of
Environmental Science and Health: Part A, 43: 714-724.
David,T., Jason, H., Lehman, J. (2006). Carbon negative biofuels from low input- high diversity
grassland biomass. Science, 314: 1598-1600.
University of Ghana http://ugspace.ug.edu.gh
50
Day, D., Evans, R.J., Lee, J.W. and Reicosky, D. (2005). Economical CO2, SOx, and NOx
capture from fossil-fuel utilization with combined renewable hydrogen production and
large-scale carbon sequestration. Energy, 30: 2558-2579.
Demirbas, A. (2004). Effects of temperature and particle size on bio-char yield from pyrolysis of
agricultural residues. Journal of Analytical and Applied Pyrolysis, 72: 243-248.
Demirbas, A. (2006). Production and characterization of bio-chars from biomass via pyrolysis.
Energy Sources Part A, 28: 413-422.
Downie, A., Crosky, A., Munroe, P., 2009. Physical properties of biochar. In: J. Lehmann,
Joseph, S. (Editors), Biochar for Environmental Management Science and Technology.
Earthscan, London.
Eilers, R.G. (1978). Water content and water retention. P.45-50. In: Manual on soil sampling
and methods of analysis, 1st Edition, A.McKeague (Editor), Canadian Society of Soil
Science, Ottawa.
Ensyn Corporation (2009). Ensyn Corporation web site.Ensyn Corporation, Wilmington,
Delaware, USA. http://www.ensyn.com/tech.htm 17.08.09.
Evangelou, V. P. (1998). Environmental soil and water chemistry. Principles and Applications.
John Wiley and Sons Inc., New York.
Fisher R. F. and Jakobsen D. (2000). Ecology and management of forest soils. 3rd Edition, John
Wiley and Sons, New York
Friedl, A., Padouvas, E., Rotter, H. and Varmuza, K. (2005). Prediction of heating values of
biomass fuel from elemental composition. Analytica Chimica Acta, 544: 191-198.
University of Ghana http://ugspace.ug.edu.gh
51
Fushimi, C., Araki, K., Yamaguchi, Y., Tsutsumi, A. (2003). Effect of heating rate on
steamgasification of biomass 2. Thermogravimetric-mass spectrometric (TG-MS) analysis
of gas evolution. Industrial & Engineering Chemistry Research 42: 3929-3936.
Gaskin, J.W., Steiner, C., Harris, K., Das, K.C. and Bibens, B. (2008). Effect of low-temperature
pyrolysis conditions on biochar for agricultural use. Transactions of the ASABE, 51:
2061-2069.
Gaunt, J.L., Lehmann, J. (2008). Energy balance and emissions associated with biochar
sequestration and pyrolysis bioenergy production. Environmental Science Technology, 42:
4152-4158.
Glaser, B., Guggenberger, G. and Zech, W. (2004). Identifying the Pre-Columbian
anthropogenic input on present soil properties of Amazonian Dark Earth (Terra Preta). In:
Glaser, B., Woods, W. (Eds.) Amazonian Dark Earths: Explorations in Space and Time.
Springer, Heidelberg, 215 pp.
González, J .F., Román, S., Encinar, J.M., Martinéz, G. (2009) . Pyrolysis of various biomass
residues and char utilization for the production of activated carbons. Journal of Analytical
and Applied Pyrolysis,85: 134-141.
Heisey, P.W. and Mwangi, W. (1996). Fertilizer Use and Maize Production in Sub- Saharan
Africa. CIMMYT Economics Working Paper 96-01, CIMMYT, Mexico.
Hornung, A., Apfelbacher, W., Koch, W., Linek, A., Sagi, S., Schoner, J., Stohr, J., Seifert, H.,
Tumiatti,V. and Lenzi, F. (2006). Thermo-chemical conversion of straw - Haloclean
Intermediate Pyrolysis, 17thInternational Symposium on Analytical and Applied Pyrolysis,
17-21, October, 2006, Paris, France.
IEA (2007). IEA Bioenergy Annual Report 2006. International Energy Agency, Paris.
University of Ghana http://ugspace.ug.edu.gh
52
International Biochar Initiative (IBI). (2009). Draft Guidelines for a Safe Biochar Industry.
Proceedings of North American Biochar Conference. Boulder, Colorado.
Jones, D. L., Edwards-Jones, G. and Murphy, D. V. (2011). Biochar mediated alterations in
herbicide breakdown and leaching in soil. Soil Biology and Biochemistry, 43: 804-813.
Kimetu, J., Lehmann, J., Ngoze, S., Mugendi,D., Kinyangi, J., Riha, S.,Verchot, L., Recha, J.
and Pell, A. (2008). Reversibility of soil productivity decline with organic matter of
differing quality along a degradation gradient. Ecosystems, 11:726–739.
Larson, B.A., (1996). Fertilizers to support agricultural development in sub-Saharan Africa: what
is needed and why. Food Policy, 21:509-525.
Lehmann, J., da Silva Jr, J. P., Steiner, C., Nehls, T., Zech, W. and Glaser, B. (2003). Nutrient
availability and leaching in an archaeological Anthrosol and a Ferralsol of the Central
Amazon basin: fertilizer, manure and charcoal amendments. Plant Soil 2 24 49 9: 343–
357pp.
Lehmann, J., Gaunt, J. and Rondon, M. (2006). Bio-char sequestration in terrestrial ecosystems -
A review. Mitigation and Adaptation Strategies for Global Change 11(2): 403-427.
Lehmann, J. 2007. Bio-energy in the black. Frontiers in Ecology and the Environment 5: 381-
387pp.
Lehmann, J. (2007). Bio-energy in the black. Frontiers in Ecology and the Environment, 5: 381-
387.
Lehmann, J. and Joseph, S. (2009). Biochar: Environmental Management. Earthscan. United
Kingdom and United States. ISBN:978-1-84407-658-1.
University of Ghana http://ugspace.ug.edu.gh
53
Lehmann, J., Lan, Z., Hyland, C., Sato, S., Solomon, D., and Ketterings, Q. M. (2005). Long
term dynamics of phosphorus and retention in manure amended soils. Environmental
Science and Technology, 39: 6672-6680.
Liang, B., Lehmann, J., Solomon, D., Kinyangi, J., Grossman, J., O’Neill, B., Skjemstad, J.O.,
Thies, J., Luizão, F.J., Petersen, J., and Neves, E.G. (2006). Black carbon increases cation
exchange capacity in soils. Soil Science Society of America Journal, 70: 1719-1730.
Lima, I. M. and Marshall, W. E. (2005). Granular activated carbons from broiler manure:
physical, chemical and adsorptive properties. Bioresource Technology 96: 699-706.
Lima, H.N., Schaefer, C.E.R., Mello, J.W.V., Gilkes, R.J. and Ker, J.C. (2002) Pedogenesis
and pre-Colombian land use of “Terra Preta Anthrosols” (“Indian black earth”)
of Western Amazonia. Geoderma 110:1–17.
Lua, A. C., Yang, T., and Guo, J. (2004). Effects of pyrolysis conditions on the properties of
activated carbons prepared from pistachio-nut shells. Journal of Analytical and Applied
Pyrolysis, 72: 279-287.
Major, J., Rondon, M., Molina, D., Riha, S.J. and Lehmann, J. (2010). Maize yield and nutrition
during 4 years after biochar application to a Colombian savanna Oxisol. Plant and Soil,
333: 117–128.
Marschner H. (1995). Adaption of plants to adverse chemical soil conditions. p. 596-657. In
Mineral nutrition of higher plants, 2nd Edition. London. Academic Press, London.
Matzner E., Pijpers M., Holland W. and Manderscheid, B. (1998). Biogeochemistry of forested
catchment in a changing environment. Soil Science Society of America Journal, 62: 445-
454.
University of Ghana http://ugspace.ug.edu.gh
54
Murphy, J. and Riley, J.P. (1962). A modified single solution method for the determination of
phosphate in natural water. Analytical Chemistry Acta, 27:31-36.
Nartey, E., Dowuona, G.N., Ahenkorah, Y., Mermut A.R .and Tiessen, H. (1997). Amounts and
distributions of some forms of phosphorus in ferruginous soils of the Interior savanna zone
of Ghana. Ghana Journal of Agricultural Science, 30: 135-143.
Nartey, E., Matsue, N. and Henmi, T. (2000) Adsorptive mechanisms of orthosilicic acid on
nano ball allophane. Clay Science, 11, 125-136.
Ogawa, M., Okimori, Y. and Takahashi, F. (2006). Carbon sequestration by carbonization of
biomass and forestation: three case studies. Mitigation and Adaptation Strategies for
Global Cchange, 11: 429-444.
Okimori, Y., Ogawa, M., Takahashi, F., 2003. Potential of CO2 emission reductions by
carbonizing biomass waste from industrial tree plantation in south Sumatra , Indonesia.
Mitigation and Adaptation Strategies for Global Change, 8: 261-280.
Olsen, S.R. and Watanabe, F.S. (1965). Test of an ascorbic acid method of determining
phosphorus in water and extracts from the soil. Soil Sci. Am. Proc. 26:677-678.
Prins, M.J., Ptasinski, K.J. and Janssen, F.J.J.G. (2006). Torrefaction of wood Part 2. Analysis of
products. Journal of Analytical and Applied Pyrolysis, 77: 35-40.
Purseglov, J. W. 1972. Tropical crops. monocots. Longman Scientific and Technical, London.
607pp.
Rondon, M.A., Lehmann, J., Ramirez, J. and Hurtado, M. (2007). Biological nitrogen fixation
by common beans (Phaseolus vulgaris L.) increases with biochar additions. Biology and
Fertility of Soils, 43: 699–708.
Schnitzer, M.I., Monreal, C.M., Facey, G.A., and Fransham, P.B. (2007) The conversion of
chicken manure to bio-oil by fast pyrolysis I. Analyses of chicken manure, biooils and char
University of Ghana http://ugspace.ug.edu.gh
55
by 13C and 1H NMR and FTIR spectrophotometry. Journal of Environmental Science and
Health, Part B: Pesticides, Food Contaminants and Agricultural Wastes 42 (1): 71-77.
Shackley, S. and Sohi, S. (2010). Benefits and Issues Associated with the Application of
Biochar to Soil. Department for Environment, Food and Rural Affairs, UK Government,
London.
Shackley, S., Carter, S., Knowles, T., Middelink, E., Haefele, S. and Haszeldine, S. (2011)
Sustainable gasification-biochar systems? A case-study of rice-husk gasification in
Cambodia, Part II: Field trial results, carbon abatement, economic assessment and
conclusions. Energy Policy doi:10.1016/j.enpol.2011.11.023.
Shinogi, Y., Yoshida, H., Koizumi, T., Yamaoka, M. and Saito, T. (2002). Basic characteristics
of low-temperature carbon products from waste sludge. Advances in Environmental
Research, 7: 661-665.
Shisanya, C.A., Mucheru, M.W., Mugendi, D.N. and Kung’u, J.B. (2009). Effect of organic and
inorganic nutrient sources on soil mineral nitrogen and maize yields in central highlands of
Kenya. Soil Tillage Research, 103: 239-246.
Sjöström, E. (1993). Wood Chemistry: Fundamentals and Applications. 2nd Edition, Academic
Press, San Diego.
Sohi, S., Lopez-Capel, E., Krull, E. and Bol, R. (2009). Biochar, climate change and soil: A
review to guide future research., CSIRO Land and Water Science Report Rep. No. 05/09,
Geln Osmond, Australia.
Sokchea H., Khieu B. and Preston, T. R. (2012). Effect of biochar from rice husks (combusted in
a downdraft gasifier or a paddy rice dryer) on production of rice fertilized with biodigester
University of Ghana http://ugspace.ug.edu.gh
56
effluent or urea. Livestock Research for Rural Development. Volume 24, Article #012,
http://www.lrrd.org/lrrd24/1/sokc24012.htm
Spokas, K.A. and Reicosky, D.C. (2009). Impacts of sixteen different biochars on soil
greenhouse gas production. Annals of Environmental Science, 3:179–193.
Steiner, C.,Teixeira, W.G., Lehmann, J., Nehls, T., Macedo, J. L.V., Blum,W. E. H. and Zech,
W. (2007). Long term effects of manure, charcoal and mineral fertilization on crop
production and fertility on a highly weathered Central Amazonian upland soil. Plant and
Soil, 291: 275–290.
Tomaszewski, J.E., Werner, D. and Luthy, R.G. (2007). Activated carbon amendment as a
treatment for residual DDT in sediment from a superfund site in San Francisco Bay,
Richmond, California, USA. Environmental Toxicology and Chemistry, 26: 2143–2150.
Tisdale, S. L., Nelson, W. L., Beaton, J. D. and Havlin, J. L. (2002). Soil Fertility and
Fertilizers.5th Edition.Prentice Hall.New Delhi-India.pp 109-172.
Ueno, M., Kawamitsu, Y., Komiya, Y. and Sun, L. (2007). Carbonisation and gasification of
bagasse for effective utilisation of sugarcane biomass. International Sugar Journal, 110: 22-
26.
Van Zwieten, L., Singh, B., Joseph, S., Kimber, S., Cowie, A., and Chan, K. Y. (2009). Biochar
and emissions of non-CO2 greenhouse gases from goil. In: J. Lehmann, Joseph, S.
(Editors), Biochar for Environmental Management Science and Technology. Earthscan,
London.
Winsley P. (2007). Biochar and bionenergy production for climate change. New Zealand Science
Review, 64: 1-10.
University of Ghana http://ugspace.ug.edu.gh
57
Yaman, S. (2004). Pyrolysis of biomass to produce fuels and chemical feedstocks. Energy
Conversion and Management, 45: 651-671.
Yanai, Y., Toyota, K. and Okazaki, M. (2007). Effects of charcoal addition on N2O emissions
from soil resulting from rewetting air-dried soil in short-term laboratory experiments:
Original article. Soil Science and Plant Nutrition, 53: 181-188.
Yu, C., Tang, Y., Fang, M., Luo, Z., and Ceng, K. (2005). Experimental study on alkali emission
during rice straw Pyrolysis. Journal of Zhejiang University (Engineering Science) 39:
1435-1444.
University of Ghana http://ugspace.ug.edu.gh
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APPENDIX
Analysis of variance
Variate: AP_mg_kg
Source of variation d.f. s.s. m.s. v.r. F pr.
Biochar_Type 2 85119.487 42559.743 38151.16 <.001
Residual 6 6.693 1.116
Total 8 85126.180
Analysis of variance
Variate: Ca
Source of variation d.f. s.s. m.s. v.r. F pr.
Biochar_Type 2 88.496257 44.248128 29571.04 <.001
Residual 6 0.008978 0.001496
Total 8 88.505235
Analysis of variance
Variate: Co
Source of variation d.f. s.s. m.s. v.r. F pr.
Biochar_Type 2 4.067E-05 2.033E-05 91.50 <.001
Residual 6 1.333E-06 2.222E-07
Total 8 4.200E-05
Analysis of variance
Variate: Cu
Source of variation d.f. s.s. m.s. v.r. F pr.
Biochar_Type 2 4.250E-02 2.125E-02 3608.89 <.001
Residual 6 3.533E-05 5.889E-06
Total 8 4.254E-02
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Analysis of variance
Variate: EC_S_cm
Source of variation d.f. s.s. m.s. v.r. F pr.
Biochar_Type 2 22435162.2 11217581.1 37860.58 <.001
Residual 6 1777.7 296.3
Total 8 22436939.9
Analysis of variance
Variate: Fe
Source of variation d.f. s.s. m.s. v.r. F pr.
Biochar_Type 2 2.01597156 1.00798578 11022.93 <.001
Residual 6 0.00054867 0.00009144
Total 8 2.01652022
Analysis of variance
Variate: K
Source of variation d.f. s.s. m.s. v.r. F pr.
Biochar_Type 2 0.735022 0.367511 351.87 <.001
Residual 6 0.006267 0.001044
Total 8 0.741289
Analysis of variance
Variate: Mg
Source of variation d.f. s.s. m.s. v.r. F pr.
Biochar_Type 2 0.598627 0.299313 41.73 <.001
Residual 6 0.043033 0.007172
Total 8 0.641660
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Analysis of variance
Variate: Mn
Source of variation d.f. s.s. m.s. v.r. F pr.
Biochar_Type 2 0.2038136 0.1019068 693.77 <.001
Residual 6 0.0008813 0.0001469
Total 8 0.2046949
Analysis of variance
Variate: Na
Source of variation d.f. s.s. m.s. v.r. F pr.
Biochar_Type 2 1.618E+03 8.088E+02 2.443E+05 <.001
Residual 6 1.987E-02 3.311E-03
Total 8 1.618E+03
Analysis of variance
Variate: TN_g_kg
Source of variation d.f. s.s. m.s. v.r. F pr.
Biochar_Type 2 1.759E-03 8.796E-04 1077.07 <.001
Residual 6 4.900E-06 8.167E-07
Total 8 1.764E-03
Analysis of variance
Variate: TOC_g_kg
Source of variation d.f. s.s. m.s. v.r. F pr.
Biochar_Type 2 0.9325087 0.4662543 556.68 <.001
Residual 6 0.0050253 0.0008376
Total 8 0.9375340
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Analysis of variance
Variate: TP_mg_kg
Source of variation d.f. s.s. m.s. v.r. F pr.
Biochar_Type 2 1538.7089 769.3544 6294.72 <.001
Residual 6 0.7333 0.1222
Total 8 1539.4422
Analysis of variance
Variate: Zn
Source of variation d.f. s.s. m.s. v.r. F pr.
Biochar_Type 2 3.458E-02 1.729E-02 4322.11 <.001
Residual 6 2.400E-05 4.000E-06
Total 8 3.460E-02
Analysis of variance
Variate: pHKCl
Source of variation d.f. s.s. m.s. v.r. F pr.
Biochar_Type 2 23.3692667 11.6846333 36262.66 <.001
Residual 6 0.0019333 0.0003222
Total 8 23.3712000
Analysis of variance
Variate: pHW
Source of variation d.f. s.s. m.s. v.r. F pr.
Biochar_Type 2 9.5524667 4.7762333 39078.27 <.001
Residual 6 0.0007333 0.0001222
Total 8 9.5532000
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