DYNAMICS OF SOIL CARBON SEQUESTRATION UNDER OIL PALM 
PLANTATIONS OF DIFFERENT AGES 

 

 

 

 

 

BY 

 

 

 

 

BRAHENE SEBASTIAN WISDOM 

(10230192) 

 

 

 

 

 

THIS THESIS IS SUBMITTED TO THE UNIVERSITY OF GHANA, LEGON IN 
PARTIAL FULFILLMENT OF THE REQUIREMENT FOR THE AWARD OF A 

MASTER OF PHILOSOPHY OF SOIL SCIENCE DEGREE 

 

 

JULY, 2013 

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DEDICATION 

To the greater glory and honour of God the Father Almighty 

and 

Mr. Kumi Prosper, Madam Esther Atukey and Mr. Aseweh Samuel 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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DECLARATION 

I hereby declare that this thesis has been written by me and that this 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 references to the authors and all assistance 

received also acknowledged. 

 

 

………………………………………………………………………. 

Brahene Sebastian Wisdom 

(Student) 

 

 

………………………………………………………………………. 

Prof. E. Owusu-Bennoah 

(Main supervisor) 

 

 

……………………………………………………………………….. 

Prof. Mark K. Abekoe 

(Co-supervisor) 

 

 

 

 

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ACKNOWLEDGEMENT 

First and foremost to the Most Holy Trinity who have been of immense help in their own unique 

ways to bring me this far. 

I would like to acknowledge the effort of my main supervisor, Prof. Emmanuel Owusu-Bennoah 

for his financial and material support towards this research work. I would also like to appreciate 

the effort and assistance of my co-supervisor, Prof. Mark K. Abekoe in providing guidance and 

encouragement during the period of my research. 

I would like to acknowledge the financial support I received towards this research from WAAPP 

through Mr. Alex Boateng who allowed me to make use of part of his remaining scholarship. 

A big thanks to all senior members of the Department of Soil Science especially the head, Dr. 

T.A. Adjadeh for facilitating the provision of chemicals and reagents for laboratory analyses. 

Thank you Uncle Julius and all other technicians of the department for your assistance. 

I would like to say thank you to my parents Mr. And Mrs. Jonas Brahene and siblings- Rebecca 

and Edmund for all that they had to sacrifice for my sake. I wish you God’s blessings. 

Thank you to Prof. Paul Vlek of WASCAL for his insightful contributions and guidance without 

which this work would not have been done. Also to Prof. Ofosu Budu of Forest and Horticultural 

Crops Research Centre, Kade for his great assistance and encouragement. God richly bless you. 

To the director and staff of the Council for Scientific and Industrial Research Institute (CSIR)-

Oil Palm Reseaech Institute (OPRI), Kusi, Ghana for their immense support and care most 

especially Madam Salo, Comfort, Papa Jay, Madam Faustie, Auntie Maggie, Auntie Agyeiwa, 

Auntie Afia Tamakloe, Mr. Boateng, Mr. Ampaabeng, Mr. Eduamah, Bro. Ekow and Red. 

Many thanks to my farmers: Mama Arku, Bursar, Atta mame, Sakyi, Abebe, Nana Awuah, 

Cudjoe, Afaga, Gyasiwaa, Uncle Ebo, Stephen, Yaw Agyei and Ablavi. 

Thank you to the following for their invaluable support- Efo Mensah, Mr. Aguze and Mr. Wiafe. 

I would like to acknowledge the assistance of my course mates, Abigail, Daniel, Koomson, 

Darko, Atibila, Moses, Harris and Bernice who is currently in Australia. 

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To the following persons: Auntie Dora, Ewoenam, Mrs. Charity Amponsah, Fish, Washing, 

Jack, Adoley, Baabah, Dr. Judith Stephens, Mr. and Mrs. Bawah, Grace, Justin, Doreen, Nana 

Koiwa, Yevu, Daniel, Esther (DSS, UG), Edem, Francis, Judith and Tracy. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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ABSTRACT 

It has been estimated that globally a lot of forest is lost in the tropics annually to agriculture. The 

removal of the forest cover has been cited as one of the main contributors of greenhouse gases. 

Tree plantations are advocated as carbon (C) sink, however, little is known about rates of C 

turnover and sequestration into soil organic matter under tropical tree plantations particularly oil 

palm. One of the commonest management practices adopted by farmers on oil palm plantations 

involves the prunning of the palm branches and heaping them in between the palm trees in the 

rows. The spaces or the alleys between the palm trees contained no heaped branch residues. So 

far very few studies have been conducted to assess the contributions of pruned branches heaped 

at the different locations under the palm plantations to the fertility status of the soil. The 

objective of this research was to assess the dynamics of soil C sequestration under oil palm 

(Elaeis guineensis) plantations at different ages in a semi deciduous forest zone of Ghana. A 

diagnostic field study was carried out to identify oil palm plantations at different ages occurring 

within the Kwaebibirem District, Ghana. The oil palm plantations were categorised into five age 

groups (0-5, 5-10, 10-15, 15-20 and 20-25 years). A forest reserve which had not been cultivated 

for more than 50 years served as a control. All the cultivated farms and the control plot were 

located at the valley bottom slope on Oda soil series (Aeric Endoaquent). Soil samples were 

collected under the heaped branches and from the spaces between the palm trees at a depth of 0-

10 and 10-20 cm respectively. The control soil from uncultivated plot was also taken at the same 

depth. The soil samples were collected for bulk density (BD) and organic C determinations. 

Carbon stocks were calculated using measured C content and the corresponding soil bulk 

densities. The presence of the residue resulted in lower BD values under heaps than those under 

alleys with age irrespective of the depth. The OC in the soil decreased with cultivation but was 

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drastic after 5 years of plantation establishment up to age 20 years in both layers under heaps 

with losses accounting for between 13-45% of the control. In the alleys the OC losses were 

greater with age in both depths with the lower layer having OC deficit of 57%. The conversion of 

the forest into the oil palm plantation led to a dramatic loss in soil C stocks of around 45% in the 

top 10cm irrespective of heap or alley location. In the 10-20cm layer loss was 50-60% with 

lower decline under residue heaps. Under heaps significant improvements in the C stocks in the 

top layer is discernible after 20 years but not in the alleys. The carbon saturation deficit followed 

a similar trend as the C stocks. The conclusion from this study is that oil palm plantations have 

the ability to sequester carbon over a period of time when palm fronds are added to the soil.  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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TABLE OF CONTENT 

Contents              Page 

DEDICATION ................................................................................................................................. i 

DECLARATION ............................................................................................................................ ii 

ACKNOWLEDGEMENT ............................................................................................................. iii 

ABSTRACT .................................................................................................................................... v 

TABLE OF CONTENT ................................................................................................................ vii 

LIST OF TABLES ......................................................................................................................... xi 

LIST OF FIGURES ...................................................................................................................... xii 

LIST OF APPENDICES .............................................................................................................. xiii 

CHAPTER ONE ............................................................................................................................. 1 

1.0     INTRODUCTION ........................................................................................................... 1 

CHAPTER TWO ............................................................................................................................ 4 

LITERATURE REVIEW ............................................................................................................... 4 

2.0 Introduction ...................................................................................................................... 4 

2.1 Oil palm ........................................................................................................................... 4 

2.1.1 Historical Development of oil palm .......................................................................... 4 

2.1.2 Modern developments in oil palm ............................................................................ 5 

2.1.3 Economic importance ............................................................................................... 7 

2.1.4 Social and environmental impact of oil palm ........................................................... 8 

2.1.5 Oil palm and carbon balance................................................................................... 10 

2.2 Carbon in soils ................................................................................................................ 11 

2.2.1 Forms of Carbon in soils ......................................................................................... 11 

2.2.2 Fate of soil organic carbon ...................................................................................... 13 

2.3 Effect of organic matter on soil properties ..................................................................... 14 

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2.3.1 Soil Biological properties ....................................................................................... 14 

2.3.2 Soil chemical properties .......................................................................................... 15 

2.3.3 Soil physical properties ........................................................................................... 15 

2.4 Effect of temperature on soil organic carbon ................................................................. 16 

2.5 Moisture and soil organic matter turnover ..................................................................... 20 

2.6 Soil type and soil organic matter turnover ..................................................................... 22 

2.7 Effect of microorganisms on soil organic carbon .......................................................... 23 

2.8 Soil carbon sequestration under forests and plantations ................................................ 25 

2.9 Carbon sequestration under a chronosequence .............................................................. 28 

2.10 Carbon studies under oil palm in Africa ........................................................................ 29 

2.11 Summary ........................................................................................................................ 30 

CHAPTER THREE ...................................................................................................................... 31 

MATERIALS AND METHODS .................................................................................................. 31 

3.1 Site selection and description ......................................................................................... 31 

3.1.1 Site selection ........................................................................................................... 31 

3.1.2 Site description........................................................................................................ 33 

3.1.3 Prevailing climate of Kwaebibirim district ............................................................. 33 

3.1.4 Soil description ....................................................................................................... 34 

3.1.5 Sample collection and preparation .......................................................................... 34 

3.2 Soil physical properties .................................................................................................. 36 

3.2.1 Bulk density (ρb) determination ............................................................................. 36 

3.2.2 Particle size analysis ............................................................................................... 36 

3.3 Soil chemical properties ................................................................................................. 37 

3.3.1 Determination of pH water (1:1)............................................................................. 37 

3.3.2 Determination of pH CaCl2 (1:2) ............................................................................ 38 

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3.3.3 Determination of organic carbon in the soil ........................................................... 38 

3.3.4 Determination of total nitrogen in the soil .............................................................. 39 

3.3.5 Determination of exchangeable bases ..................................................................... 40 

3.3.6 Determination of cation exchange capacity (CEC) ................................................ 42 

3.4 Calculation for C stocks ................................................................................................. 42 

3.5 Calculation for carbon saturation deficit ........................................................................ 43 

3.5 Calculation for carbon changes (dynamics) ................................................................... 43 

3.6 Calculation for average C increment per year ................................................................ 43 

3.7 Data analysis .................................................................................................................. 43 

CHAPTER FOUR ......................................................................................................................... 45 

RESULTS ..................................................................................................................................... 45 

4.0 Introduction .................................................................................................................... 45 

4.1 Physical and chemical properties of the uncultivated (reference) and cultivated soils .. 45 

4.2 Effect of oil palm prunnings and heapings on the physico-chemical properties of the 

soils                                                                                                                                         47 

4.3 Physico-chemical properties of soils under oil palm alleys ........................................... 50 

4.4 Bulk density, Total N, C content and stocks in soils under prunnings .......................... 53 

4.5 Bulk density, Total N, C content and C stocks in soils within the alleys ...................... 57 

CHAPTER FIVE .......................................................................................................................... 60 

DISCUSSION ............................................................................................................................... 60 

5.0 Introduction .................................................................................................................... 60 

5.1 Soil characteristics of all soils ........................................................................................ 60 

5.1.1 Soil textural characteristics ..................................................................................... 60 

5.1.2 Soil pH .................................................................................................................... 60 

5.1.3 Exchangeable bases and cation exchange capacity (CEC) ..................................... 61 

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5.1.5 Organic carbon content ........................................................................................... 64 

5.1.6 Total nitrogen content ............................................................................................. 66 

5.2 Carbon to nitrogen (C: N) ratio ...................................................................................... 69 

5.3 Carbon stocks ................................................................................................................. 72 

5.4 Relationship between C and management options:........................................................ 72 

5.5 C saturation deficit ......................................................................................................... 75 

5.6 Carbon dynamics and increments .................................................................................. 77 

CHAPTER SIX ............................................................................................................................. 79 

SUMMARY, CONCLUSION AND RECOMMENDATION ..................................................... 79 

6.1 Summary ........................................................................................................................ 79 

6.2 Conclusion ...................................................................................................................... 81 

6.3 Recommendations .......................................................................................................... 82 

REFERENCES ............................................................................................................................. 83 

APPENDICES ............................................................................................................................ 112 

 

 

 

 

 

 

 

 

 

 

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LIST OF TABLES 

Table 4. 1 Physico-chemical properties of soils under cultivated and uncultivated sites ............. 46 

Table 4. 2 Physico-chemical properties of soils under heaps ....................................................... 48 

Table 4. 3 Physico-chemical properties of soils within the oil palm alleys .................................. 51 

Table 4. 4 Bulk density, Total Nitrogen, C content and stocks for 0-10 and 10-20 cm layers under 

heaps. ............................................................................................................................................ 54 

Table 4. 5 Changes in C stocks under heaps with age of plantation ............................................. 54 

Table 4. 6 Bulk density, Total Nitrogen, C content and stocks for 0-10 and 10-20 cm layers under 

alleys. ............................................................................................................................................ 58 

Table 4. 7 Changes in C stocks under alleys with age of the oil plantations ................................ 58 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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LIST OF FIGURES 

Fig. 3. 1 Location of farms territory and sampled plots. ............................................................... 32 

Fig. 3. 2 shows prunnings in between the stands and alleys under an oil palm plantation. .......... 44 

Fig. 5. 1 (a) and (b) show relationships between CEC (cmolc/kg soil) and C content (g/kg soil) in 

the 0-10 and 10-20 cm layers respectively under prunnings.             62 

Fig. 5. 2 (a) and (b) show relationships between CEC (cmolc/kg soil) and C content (g/kg soil) in 

the 0-10 and 10-20 cm layers respectively under alleys. .............................................................. 63 

Fig. 5. 3 Relationships between Total N content (g/kg soil) and C content (g/kg soil) in the (a) 0-

10 cm layer and (b) 10-20 cm layer under prunnings. .................................................................. 67 

Fig. 5. 4 Relationships between Total N content (g/kg soil) and C content (g/kg soil) in the (a) 0-

10 cm layer and (b) 10-20 cm layer under alleys. ......................................................................... 68 

Fig. 5. 5 Relationships between C/N ratio and C content (g/kg soil) in the (a) 0-10 cm layer and 

(b) 10-20 cm layer under prunnings.............................................................................................. 70 

Fig. 5. 6 Relationships between C/N ratio and C content (g/kg soil) in the (a) 0-10 cm layer and 

(b) 10-20 cm layer under alleys. ................................................................................................... 71 

Fig. 5. 7 shows carbon stocks in the (a) 0-10 cm layer and (b) 10-20 cm layer under prunnings 

for the different age groups. .......................................................................................................... 73 

Fig. 5. 8 shows carbon stocks in the (a) 0-10 cm layer and (b) 10-20 cm layer under alleys for the 

different age groups. ..................................................................................................................... 74 

Fig. 5. 9 Carbon saturation in the (a) 0-10 cm layer and (b) 10-20 cm layer under prunnings for 

the different age groups. ............................................................................................................... 75 

Fig. 5. 10 Carbon saturation in the (a) 0-10 cm layer and (b) 10-20 cm layer under alleys for the 

different age groups. ..................................................................................................................... 76 

 

 

 

 

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LIST OF APPENDICES 

Appendix A: Summary information of selected sites     114 

Appendix B: Analysis of variance (ANOVA) tables     115 

Appendix C: Questionnaire         130 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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CHAPTER ONE 

1.0     INTRODUCTION 

Farming system transformations with the introduction of cash crops have led to permanent 

cultivation of agricultural lands during the last decades, (Serpantié, 2003). Oil palm is one of the 

plantation crops grown in Ghana in addition to cocoa and rubber. This has been undertaken by 

companies such as the Benso Oil Palm Plantation (BOPP) in the Western Region, Ghana Oil 

Palm Development Company (GOPDC) at Kade in the Eastern Region, Twifo Oil Palm 

Plantation at Twifo, Central Region and also by other private companies as well as small holder 

farmers either in groups or as individuals. The production of oil palm has led to the conversion of 

natural vegetation into oil palm plantations. It is expected that the conversion of some rain 

forests and use of abandoned logged-off forests into oil palm plantations might have significantly 

contributed to losses in C from both soil and vegetation into the atmosphere. 

Some studies (Ollagnier et al., 1978; Olivin, 1980; Djegui et al., 1992; Haron et al., 1998) 

carried out under Ivorian conditions have measured changes in soil C content from destruction of 

the forest ecosystem to its replacement by an oil palm plantation. They observed that when such 

a replacement was made, there was a notable drop in soil carbon in the first 4 years as the young 

oil palms develop, then that rate seems to stabilize from 9 years old onwards. 

If the effects of global warming are to be kept to a minimum, carbon already emitted to the 

atmosphere as a result of conversion of large tracts of natural rain forest vegetation into oil palm 

plantations must be sequestered into stable forms. According to Lal, (2009) C sequestration is 

enhanced when the input of C into the system exceeds the amount of C that is lost due to plant 

harvest, physiological respiration, mineralisation, erosion, and leaching. The rate of C 

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sequestration is determined by the net balance between C inputs and C outputs. Carbon inputs 

and outputs are affected by management e.g. heaping of pruned branches and by two biotic 

processes- production of organic matter in the soil and decomposition of organic matter by soil 

organisms. 

During cultivation of oil palm local farmers engage in prunning and the heaping of palm fronds 

in between the rows of plants. Most of these farmers do not add any external source of fertiliser 

to their farms. The heaping of palm fronds have been observed to be sources of organic material 

addition to the soil since organic resources have been found to play a vital role in the 

maintenance of soil organic matter (SOM) and nutrient cycling in most smallholder and large 

scale oil palm farming systems in the tropics (McNeil et al., 1997; Cadisch et al., 2002b). This 

management practice by farmers serves as a potential means of contributing C to the soil under 

oil palm. From an agro-ecological perspective, OM and its main constituent carbon play a crucial 

role in the functioning of these systems. They actually affect physical, chemical and biological 

properties of soils (Batjes, 2001; Feller et al., 2001). 

From an environmental point of view, soil is an element of the global carbon cycle even if it 

seems that a dilemma still exists. The desire to increase SOM arises from the global climate issue 

whiles the desire to decrease it arises from agronomic needs as nutrient sinks for plants (Janzen, 

2006). A change therefore in management practices such as heaping of pruned branches leading 

to an increase in C stocks (sinks) represents a means to reduce CO2 concentration in the 

atmosphere which is responsible for the increase of the Earth’s surface temperature (GIECC, 

1997). It is therefore imperative that SOM which is an important resource is well managed for 

agronomic and environmental challenges. 

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There is a need to assess the soil quality under smallholder oil palm plantations with particular 

reference to prunning and heaping of branches on farms. This has arisen because of poor 

management of oil palm prunnings in many of the smallholder farms leading to low soil fertility 

affecting yield. There is also a need to sequester C to overcome global climate change (Paustian 

et al., 1998a) and to improve soil quality, as we develop more sustainable and land management 

practices under oil palm (Carter, 2002). 

So far there appears to be no information on soil carbon studies under pruned heaps on oil palm 

plantations in Ghana. There is also lack of information on C dynamics under this management 

system with age of the plantations. There is therefore the need to assess how management 

activities (prunning and heaping) undertaken by local farmers influence organic carbon stocks in 

the soil under oil palm plantations at the smallholder farms in Ghana. 

The hypothesis of the study is that, management practice of prunning and heaping of fronds of 

oil palm trees in between the palms could serve as a means of building C in the soil and thereby 

minimising C emissions into the atmosphere. 

The objectives of this research are: (1) to assess soil C content and stocks under pruned heaps in 

already established oil palm plantations of different maturity ages; (2) to examine the dynamics 

(changes) in soil C stocks over time under pruned heaps in these oil palm plantations. 

 

 

 

 

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CHAPTER TWO 

LITERATURE REVIEW 

2.0 Introduction 

This chapter critically aims at looking through available literature to find out works that have 

been done in relation to soil carbon sequestration under oil palm plantations under similar 

environmental (tropical) conditions. The review also aims at bringing to light all relevant 

information in relation to the topic and would look at past and current trends and possibly future 

events that are likely to occur. It also involves identifying the gaps that exist in the various 

researches that have been undertaken and how a suitable and appropriate approach can be taken 

to guide the undertaking of this research. The review would be in three main sections:  

 (i) the historical background, agronomy and economic benefits of the oil palm tree 

 (ii) the presence and role of carbon in the soil      

 (iii) the various factors and agents that directly or indirectly affect carbon present in soil 

2.1 Oil palm 

2.1.1 Historical Development of oil palm 

The Oil Palm of commerce, Elaeis guineensis, is believed to be indigenous to West Africa (the 

specific name, guineensis shows that the first specimen described was collected in Guinea, West 

Africa) (USDA GRIN Taxonomy 2013). The closely related American oil palm Elaeis oleifera is 

also used to a lesser extent to produce palm oil, and a more distantly related palm Attalea maripa 

is another oil-producing palm (Zahara et al., 2009). Human use of oil palms may date as far back 

as 5,000 years in West Africa; in the late 1800s, archaeologists discovered palm oil in a tomb at 

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Abydos dating back to 3,000 BCE (Kiple and Corneeornelas, 2000). It is thought that Arab 

traders brought the oil palm to Egypt (Obahiagbon, 2012). Oil palms were introduced to Java by 

the Dutch in 1848, Lötschert and Beese (1983) and to Malaysia (then the British colony of 

Malaya) in 1910 by Scotsman William Sime and English banker Henry Darby. The species of 

palm tree Elaeis guineensis was taken to Malaysia from Eastern Nigeria in 1961. The southern 

coast of Nigeria was originally called the Palm oil coast by the first Europeans who arrived there 

and traded in the commodity. This area was later renamed the Bight of Biafra. There is a general 

consensus that commercially planted palms in Indonesia, Malaysia and other South–East Asian 

locations were derived from four West African Palm varieties including E. guineensis fo. dura, 

E. guineensis var. pisifera, E. guineensis fo. tenera. 

2.1.2 Modern developments in oil palm 

Planting materials currently used in commercial oil palm plantations consist of Tenera palms or 

D x P hybrids, which are obtained by crossing Dura (thick shelled) with Pisifera (shell-less) 

(Tweneboah, 2000). Instances were common when commercially germinated seed with thick-

shell as the Dura mother palm was used, the resulting palm would produce thin-shelled Tenera 

fruit. To overcome this out-crossing phenomenon is to produce tissue-culture or "clonal" palms, 

which provide "true copies" of high yielding D x P palms (Foster and Prabowo, 1996a). 

However, constraints to mass production need to be dealt with. 

It has been suggested that the right approach to oil palm development would be to introduce 

leguminous cover plants immediately after land clearing. These are meant to prevent soil erosion 

and surface run-off, improve soil structure and palm root development, increase the response to 

mineral fertilizer in later years, and reduce the danger of micronutrient deficiencies. Leguminous 

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cover plants also help prevent outbreaks of Oryctes beetles, which breed in exposed 

decomposing vegetation (AsySyura and Tsan, 2009). There is a severe setback associated with 

young palms in areas where grasses are allowed to dominate the inter-row vegetation, more so on 

poor soils where the correction of nutrient deficiencies is difficult and costly (Foster and Goh, 

1997). 

According to Tweneboah (2000), oil palm does well under equatorial climate between latitude 

10o North and 10o south of the Equator. It is within this region that the biggest area of semi-wild 

Elaeis guineensis groves in the lowland regions of Western Africa lie. This region is 

characterised by mean annual rainfall of 2000 mm with no severe dry season, minimum 

temperature not below 22oC and maximum temperatures between 29-33oC. In addition sunshine 

should be at least five hours per day rising to about seven hours during special months in the year 

to support high oil palm production. Asamoah and Nuertey (1998a; 1998b) have outlined a 

description of some Ghanaian soils within Kusi, Twifo Praso and Adum which are suitable for 

large scale oil palm production. Further, Asamoah and Nuertey (2005) have shown that oil palm 

does well in areas considered as marginal and unsuitable within the forest zone of Ghana. 

Successful oil palm development involves selecting a suitable soil even though oil palm does 

well on a wide variety of soils ranging from well drained deep loams to sandy loams and sandy 

clay loams having pH below 6. Oxisols and Ultisols both highly weathered deep soils occur in 

oil palm growing areas in Guinea-Bissau, Sierra Leone, Liberia, Southern Cote d’ Ivoire, South 

eastern and western part of Ghana and South eastern Nigeria. However, Oxisols have been 

reported as being best for oil palm production (Tweneboah, 2000). 

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According to Tinker (1976) nutrient requirements of oil palm vary directly depending on yield 

target set, type of planting material used, spacing, age, soil type, ground cover conditions in 

addition to good climate and associated environmental factors. Nutrient demand can therefore be 

grouped according to:          

 1. That removed in the harvested crop (fruit bunch)     

 2. That immobilised in the palm biomass       

 3. That recycled to the soil in pruned fronds, male inflorescence and leaf wash. 

After successful pollination, it takes about five to six months for fruits to mature. Matured fruits 

are reddish in colour about the size of a large plum and occur in a large bunch. Examination of a 

fruit reveals an oily fleshy outer layer (pericarp) with a single seed (palm kernel) with an inner 

portion rich in oil. A fully matured ripe bunch weighs between 40-50 kg (Fairhurst and 

McLaughlin, 2009). 

2.1.3 Economic importance 

Oil is extracted from both the pulp of the fruit (palm oil, an edible oil) and the kernel (palm 

kernel oil, used in foods and soap manufacture). For every 100 kg of fruit bunches, typically 22 

kg of palm oil and 1.6 kg of palm kernel oil can be extracted (Fairhurst and McLaughlin, 2009). 

Also, high oil yield of oil palms (up to about 7,250 litres per hectare per year) has made it a 

common cooking ingredient in Southeast Asia and the tropical belt of Africa. Currently, its use 

in the commercial food industry in other parts of the world has increased as a result of its cheaper 

pricing (USDA, 2006). The high oxidative stability of refined oil palm product, (Che Man et al., 

2009; Matthäus, 2007) and high levels of natural antioxidants (Sundram, 2003) make it a good 

source of raw material for the production of other items. Palm oil is known to contain more 

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saturated fat than oils from sources such as canola, corn, linseed, soybeans, sunflower and 

safflower and is able to withstand extreme heat associated with deep frying and also resists 

oxidation (Goh and Hardter, 1995). 

Malaysia was the world's largest producer in the year 1995, with a 51% of world market share, 

but since 2007, Indonesia has been the world's largest producer, supplying approximately 50% of 

world palm oil volume (USDA, 2012). Worldwide palm oil production for season 2011/2012 

was 50.3 million metric tons, increasing to 52.3 million tons for 2012/13 (USDA, 2012). In 

2010/2011, total production of palm kernels was 12.6 million tonnes (FAO, 2012). 

2.1.4 Social and environmental impact of oil palm 

Oil palm establishment and palm oil production has grown rapidly in Southeast Asia, with 

Indonesia and Malaysia currently accounting for more than 85% of global palm oil demand 

(Danielsen et al., 2009; Fargione et al., 2008). In 2006-07, production of palm oil in these two 

countries was 31.9×103 metric tonnes, rising to 41.1×103 metric tonnes in 2010-11. This increase 

has contributed to deforestation across the Southeast Asia region. Between 1990 and 2007, 5.1 

Mha of total 15.5 Mha of peatland in peninsular Malaysia and the islands of Borneo and Sumatra 

was deforested, drained and burned while most of the remainder was logged intensively 

(Langner and Siegert, 2009; Miettinen and Liew, 2010). Over the same period, industrial oil 

palm and pulpwood (Acacia) plantations expanded dramatically from 0.3 Mha to 2.3 Mha (likely 

comprising 2.1 Mha of oil palm and 0.2 Mha of Acacia), an increase from 2-15% of the total 

peatland area (Miettinen and Liew, 2010). 

Any discussion on the social and environmental impacts of oil palm cultivation is highly 

controversial. According to Malaysian Palm Oil Council (2013); Friends of the Earth, (2007) and 

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Fitzherbert et al., (2008) oil palm is a valuable economic crop and provides a major source of 

employment. It allows many small landholders to participate in the cash economy and often 

results in the upgrade of the infrastructure (schools, roads, and telecommunications) within that 

area. However, there are instances where native customary lands have been appropriated by oil 

palm plantations developers without any form of consultation or compensation leading to social 

conflict between the plantations developers and local residents (iDMC, 2007). In some cases, 

labour for oil palm plantation establishment are dependent on imported labour or illegal 

immigrants, with some concerns about the employment conditions and social impacts of these 

practices (Forest Peoples Programme, 2009).  

Biodiversity loss (including the potential extinction of charismatic species) is one of the most 

serious negative effects of oil palm cultivation. Large areas of already threatened tropical 

rainforest are often cleared to make way for oil palm plantation development, especially in 

Southeast Asia, where enforcement of forest protection laws is lacking. In some countries where 

oil palm is established, lax enforcement of environmental legislation have led to encroachment of 

plantations into protected areas (UNEP, 2007), encroachment into riparian strips (New Straits 

Times, 2007) and release of palm mill pollutants such as palm oil mill effluent (POME) in the 

environment (New Straits Times, 2007). Some of these states have recognised the need for 

increased environmental protection, resulting in more environment-friendly practices (EIA, 

2000; RSPO, 2007). Among those approaches is anaerobic treatment of POME, which can be a 

good source for biogas (methane) production and electricity generation. Anaerobic treatment of 

POME has been practised in Malaysia and Indonesia. Like most wastewater sludge, anaerobic 

treatment of POME results in dominance of Methanosaetaconcilii. It plays an important role in 

methane production from acetate, and the optimum condition for its growth should be considered 

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to harvest biogas as renewable fuel (MohdRafein, 2009). In addition, the use of palm oil as 

biofuel has been described as perverse because it encourages the conversion of natural habitats 

such as forests and peatlands, releasing large quantities of greenhouse gases (Danielsen et al., 

2009). 

2.1.5 Oil palm and carbon balance 

Oil palm production has been documented as a cause of substantial and often irreversible damage 

to the natural environment. Clay (2004) reported that the negative impacts of oil palm on the 

environment include deforestation and habitat loss of critically endangered species and a 

significant increase in greenhouse gas emissions (Bates et al., 2008). The pollution is 

exacerbated because many rainforests in Indonesia and Malaysia lie on top of peat bogs that 

store great quantities of carbon, which are released when the forests are cut down and the bogs 

are drained to make way for the plantations. 

Environmental groups, such as Greenpeace, claim the deforestation caused by making way for 

oil palm plantations is far more damaging to the climate than the benefits gained by switching to 

biofuel. According to Andre (2007) and Fargione et al. (2008), fresh land clearances, especially 

in Borneo, are contentious for their environmental impact. The BBC (2007a, 2007b) broadcast 

reported that despite thousands of square kilometres of land standing unplanted in Indonesia, 

tropical hardwood forests are being cleared for palm oil plantations. Furthermore, as the 

remaining unprotected lowland forest dwindles, developers are looking to plant peat swamp land, 

using drainage that begins an oxidation process of the peat which can release 5,000 to 10,000 

years worth of stored carbon. Drained peat is also at very high risk of forest fire. There is a clear 

record of fire being used to clear vegetation for oil palm development in Indonesia, where in 

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recent years drought and man-made clearances have led to massive uncontrolled forest fires, 

covering parts of Southeast Asia in haze and leading to an international crisis with Malaysia. 

These fires have been blamed on a government with little ability to enforce its own laws, while 

impoverished small farmers and large plantation owners illegally burn and clear forests and peat 

lands to develop the land rather than reap the environmental benefits it could offer (AFP, 2007 

and VOA news, 2007). Research conducted by the Tropical Peat Research Laboratory shows that 

oil palm plantations act as carbon sinks, converting carbon dioxide into oxygen (New Straits 

Times 2010) and according to the Malaysia's Second National Communication to the United 

Nations Framework Convention on Climate Change, the plantations contribute to Malaysia's 

status as a net carbon sink (Ministry of Natural Resources and Environment Malaysia, 2000). 

Efforts to promote sustainable cultivation of oil palm have been promoted by organizations 

including the Roundtable on Sustainable Palm Oil, (Morales, 2010) and through support for 

conservation and rehabilitation of tropical forest, including the Malaysian government, which is 

committed to preserve 50 percent of its total land area as forest (Adnan, 2013). 

2.2 Carbon in soils 

2.2.1 Forms of Carbon in soils 

Soil C comprises soil organic carbon (SOC) and soil inorganic carbon (SIC). Soil organic carbon 

is a complex and dynamic group of compounds formed from C originally harvested from the 

atmosphere by plants. During photosynthesis, plants transform atmospheric C into the forms 

useful for energy and growth through reduction of oxidized C into organic forms (Schlesinger, 

1997). Organic C then cycles from the plant to the soil, where it becomes an important source of 

energy for the ecosystem, driving many other nutrient cycles. Soil inorganic carbon is the result 

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of mineral weathering and forms a small proportion of many productive soils. It could be in the 

form of carbonates and is less responsive to management than SOC (Izaurralde, 2005). 

The Century Soil Organic Matter Model describes three main C pools: an active pool (1–5 years 

turnover time), a slow pool (20–40 years turnover time) and a passive pool (200–1500 years 

turnover time) (Parton et al., 1987). The active pool mainly represents soil microbes and 

microbial products, while slow and passive pools contain C compounds resistant to 

decomposition (Parton et al., 1987). However, experimental verification and validation of the 

modelled C pools are very important to improve the predictive capacity of the model for 

estimating long-term changes in SOC (Christensen, 1996). 

Soil organic carbon makes up between 48-58% C approximately 50% of all soil organic matter 

(SOM) (Wilke, 2005; Nelson and Sommer, 1982). Soil organic matter content is correlated with 

productivity and defines soil fertility and stability (Herrick and Wander, 1998). Most SOC is 

present in the topsoil of soil profiles as a result of the presence and influence of biotic processes 

there, with approximately 64% of soil C located in the top 50cm (Conant et al., 2001). Jones 

(2007) reported a positive correlation between SOC accumulation and precipitation and a 

negative correlation between SOC accumulation and temperature. Soil C stocks are positively 

correlated with the presence of clay and iron, and negatively correlated with bulk density of soil. 

Soil organic carbon and SOM buffer soil temperature, water quality, pH and hydrology 

(Evrendilk et al., 2004; Pattanayak et al., 2005). Increase in SOC and SOM lead to greater pore 

spaces and surface area within the soil, which subsequently retains more water and nutrients 

(Tisdale et al., 2002; Greenhalgh and Sauer, 2003). 

 

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2.2.2 Fate of soil organic carbon 

Decomposition of organic matter C can be assessed with the aid of simple models that make use 

of a single exponential decay functions to assess the changes in soil C stocks over time, eg 

 

 
��
�� = �� − �	 … … … … … … … … … … … … … … … … … … … … … … … … … … … … . … . . �2.1� 

where A = amount of C added from residue, f= fraction of A that decomposes to become soil-C 

each year, k = the fraction of soil-C decomposed each year and C = organic soil C pool 

(Jenkinson, 1981). By this, the C-storage dynamics are strongly determined by the amount and 

quality of C added. It has been estimated that about 8 t C/ha is needed to be added in residues 

annually to compensate for CO2-C respiration losses from SOM under humid tropical conditions 

(Sitompul et al., 1996). From the exponential model above, it can be seen that there exists 

equilibrium in SOC (Ce) under continuous soil management (Jenkinson, 1981):   

 
��
�� = 0−→ 	� = ��

� … … … . . … … … … … … … … … … … … … … … … … … … … … … … . . �2.2� 

Carbon stocks measured under natural vegetation have often been used as a reference for the C 

storage potential of a soil under a given climate. As land use changes with management, soil C 

often declines in relation to levels in the natural vegetation where the difference between current 

and potential C storage is expressed as the C saturation deficit (van Noordwijk et al., 1997): 

 	���������� = �����	�!�"
����

… … … … … … … … … … … … … … … … … … … … … … … … . . … . . �2.3� 

where Cref is a reference soil C level representative of a forest soil of the same texture and pH, 

and Corg is the current C stock. The saturation deficit not only depicts the potential amount of C 

that can be stored, but also influences the speed of C accumulation i.e. the closer a soil is to its 

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maximum potential C storage, the slower the C accumulation, as proportionally less C becomes 

protected. 

2.3 Effect of organic matter on soil properties 

Pierzynski et al. (2000), Baddock and Nelson (2000) have come out with three properties of soil 

(biological, chemical and physical) and how they are affected by OM. 

2.3.1 Soil Biological properties 

Mineralization-Immobilisation in soils is affected by OM. The decomposition of OM in soils 

yields NH4
+, NO3

-, PO4
3-, SO4

2-, micronutrients and CO2. This provides nutrients for plant 

growth and is also essential for the global cycling of elements such as C and N in soils. Organic 

matter plays a key role in the stimulation and inhibition of enzyme activities and of plant and 

microbial growth. Soil enzyme activity and the growth of plants and microorganisms can be 

stimulated or inhibited by the presence of humic materials which control the size, growth and 

activity of plant and microbial communities in soil. The biological diversity (biodiversity) in soil 

is affected by OM. Organic matter supports life processes for a wide range of species of 

microbes and fauna and this contributes to the functional integrity/ resilience of ecosystems. 

Organic matter present in soils act as a reservoir of metabolic energy for microorganisms and 

store of atmospheric C. It does this by providing metabolic energy for soil microorganisms and 

fauna which in turn drive biological processes (ammonification, nitrification, denitrification, 

mineralisation, and immobilisation). 

 

 

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2.3.2 Soil chemical properties 

Cation exchange which involves total exchange capacities of isolated OM fractions range from 

300 to 1400 cmol/kg and this functions to enhance retention of cations in soils. Organic matter 

present in soils plays a role in the chelation of metals which involves formation of stable 

complexes with Cu2+, Mn2+, Zn2+ and other polyvalent cations. This enhances dissolution of soil 

minerals, reduces loss of micronutrients; enhances the availability of micro- and macronutrients 

to higher plants; reduces the potential toxicity of metals. Another feature of OM is its low 

solubility in water. The insolubility is due to association of OM with clay and the hydrophobic 

nature of its constituents; also, salts of divalent and trivalent cations with OM are insoluble in 

soil water. This reduces the loss of OM through leaching in soils. Buffer action of soils is 

affected to an extent by the presence of OM when it acts as a buffer in slightly acid and alkaline 

soils. This helps to maintain many biochemical properties in acceptable range. In addition OM 

combines with xenobiotics to affect bioactivity, persistence and biodegradability of pesticides in 

soils by modifying application rates of pesticides for effective control. 

2.3.3 Soil physical properties 

Organic matter affects the physical properties of soils through combination with clay minerals 

during which it cements soil particles into aggregates. This stabilises structure, thereby reducing 

erosion and improving tilth; increase permeability of soil to gases and water. Water retention in 

soils is enhanced by OM which can hold up to 20 times its weight in water and indirectly 

contributes to water retention through its effects on soil structure. This improves moisture-

retaining properties of coarse-textured soils; helps prevent drying and shrinking. The colour of 

some soil can be used to predict the type of minerals or constituents present in them. The typical 

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dark colour of many soils is caused by OM and this facilitates warming to promote most soil 

activities. 

2.4 Effect of temperature on soil organic carbon 

Respiration activities in soils is affected in a complex way by temperature, moisture, soil 

properties, quality and quantity of decomposing organic substrates (Kirschbaum, 2000; Raich 

and Tufekcioglu, 2000), and predictions of future changes rely on detailed knowledge on the 

effects of each of these factors but also on their interaction. Soil respiration is strongly dependent 

on temperature. At the global scale CO2 efflux strongly correlates with annual mean temperature 

(Raich and Schlesinger, 1992), though it has been debated that it depicts in large a relationship 

between soil respiration and ecosystem net primary production (NPP) or gross primary 

productivity (GPP) (Kirschbaum, 2000; Janssens et al., 2001). However, at the ecosystem scale, 

e.g. in forests with no moisture stress, temperature exerts the dominant control over seasonal 

variability of soil respiration (Janssens et al., 2001). Temperature may explain up to 72–96% of 

the variation in soil respiration in temperate forests (Keith et al., 1997; Boone et al., 1998; Rey et 

al., 2002; Subke et al., 2003). Variations in temperature are a fundamental entity of the soil 

environment in the temperate zone. These variations show fast (diurnal) and slow (seasonal) 

dynamics and represent the natural environmental background of ecosystem processes. The 

range of diurnal fluctuations in litter and topsoil depends on a number of factors and can reach 

25–30 oC (Byzova, 1977). However, work by Fujii et al. (1998) showed that soil temperature in 

surface (15–50 cm depth) and subsurface (150–200 cm depth) zones varied from 12 to 33 oC and 

13 to 27 oC, respectively. 

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The size of the soil carbon pool depends on the productivity of vegetation and the decomposition 

of organic material in soil, which are both climate-dependent processes. Decomposition is 

considered to increase or decrease with increasing temperature than does net primary 

productivity of C in plant tissues (Schimel et al., 1994; Kirschbaum, 2000). For example, 

Thomson et al., (2006) have suggested that at higher temperature and precipitation, the soil 

carbon sequestration rate and the soil carbon content will increase. This further affects the 

organic material decomposition and the losses from soil are also likely to increase (Ågren and 

Hyvo¨nen, 2003). In contrast, predictions of reduced carbon input to soil at higher temperature 

have been made by Alvarez and Alvarez (2001). In addition, higher temperature and 

precipitation result in the decline of (SOC) (Grace et al., 2006), but the cumulative dissolved 

organic carbon (DOC) in the humus layer will increase (Andersson and Nilsson, 2001). The 

temperature sensitivity of soil organic carbon mineralization has recently attracted considerable 

interest because of its potential importance in the global carbon cycle. The response of SOC 

decomposition to environmental change especially to changes in temperature is of great concern, 

because the increase in atmospheric greenhouse gas concentrations and the subsequent 

temperature increase may stimulate SOC decomposition, resulting in strong positive feedback to 

global warming (e.g. Solomon et al., 2007). 

The temperature sensitivity of soil respiration has been a topic of very intense debate over recent 

years, as summarised by Davidson and Janssens (2006). There is evidence to suggest that under 

higher temperatures soil carbon decomposition will increase, thus resulting in increased CO2 

emissions from heterotrophic respiration (Knorr et al., 2005). However there is a contrasting 

opinion that soil carbon decomposition will be rather insensitive to temperature (Giardina and 

Ryan, 2000), being mostly determined by the supply rate of substrate. Much of the debate centres 

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on the temperature sensitivity of the labile versus recalcitrant fractions of the soil carbon. It has 

been suggested that the “fresh” (i.e. younger) soil carbon is more sensitive to temperature 

changes, whilst the older fraction is not sensitive, as it includes hard-to-decompose materials and 

organic matter that is protected in the interior of soil particles (Giardina and Ryan, 2000; 

Thornley and Cannell, 2001; Davidson and Janssens, 2006). Fang et al., (2005) have, however, 

shown that the recalcitrant and labile pools present in soils do not show any significant 

differences in temperature sensitivity, implying that both of these pools in the soil organic matter 

will respond similarly to global warming (Fang et al., 2005). As a large component of SOM is 

made up of such recalcitrant material, the temperature sensitivity and potential availability as a 

substrate for microbial respiration of this pool are of acute importance with respect to climate 

change (Biasi et al., 2005). Berg et al. (1993), showed that a standard pine litter produced more 

recalcitrant products of decomposition per unit of accumulated mass loss when it decomposed 

rapidly (under warm and wet conditions) than when it decomposed more slowly (in cooler and 

dryer environments). These authors also proposed that late decomposition would be slower in 

systems with high initial mass loss rates. 

Marschner and Bredow (2002) conducted a study which showed a close interaction between the 

processes of degradation and production in the control of DOC in the soil solution. In the studied 

soil, DOC was found to be the most important substrate for microorganisms and was, therefore, 

depleted during incubation. But the effects on DOC properties cannot be solely attributed to the 

selective mineralization of certain fractions or size classes as it reflected in the relative 

accumulation of UV-active compounds at higher incubation temperatures. At the same time, 

microbially produced compounds that have high metal complexing abilities and are easily 

degradable are released into the soil solution with increasing temperature and microbial 

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respiration. The nature and exact origin of these compounds is still unknown. They could be 

metabolites from degradation processes, actively released substances such as siderophores or 

biomass constituents liberated after starvation and lysis of organisms. These easily degradable 

compounds apparently can persist in the soil solution when microbial activity is reduced by 

nutrient deficiency or during adverse environmental conditions (low temperature and drought) 

and will thus enhance the availability and transport of metal micronutrients or contaminants. 

Soil temperature has been recognised as the primary factor regulating soil respiration, (RS) while 

soil moisture is secondary, its control over RS being mostly effective under extreme moisture 

values (Conant et al., 2004; Luo and Zhou, 2006; Li et al., 2008; Litton and Giardina, 2008; 

Wang et al., 2011b). Besides these two major environmental factors, the size of the soil organic 

C (SOC) pool, the quality of organic matter, the abundance of roots, and the distance from the 

nearest tree stem also affect RS and its components (i.e. heterotrophic respiration, RH and 

autotrophic respiration, RA) (Saiz et al., 2006; Wang et al., 2010b; Luan et al., 2011). Since all 

these variables are affected by the nature of the vegetation present e.g. forest cover (De Deyn et 

al., 2008), it is expected that RS, RH and RA should differ with forest composition. 

Temperature sensitivity of respiration is often expressed by Q10, the factor by which respiration 

rate increases with every 10 oC increment of temperature. The Q10-based formulation has been 

used commonly to calculate soil or ecosystem respiration from local to global scales (Cox et al., 

2000; Fang and Moncrieff, 2001; Falge et al., 2002). 

However, the response of respiration to temperature has been questioned recently (Luo et al., 

2001; Tjoelker et al., 2001). This has brought out suggestions to the point that the terrestrial 

ecosystem respiration rate has been overestimated in global carbon cycles (Cox et al., 2000). For 

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now, it still remains unclear regarding how Q10 is affected by factors other than temperature 

(Tjoelker et al., 2001; Fang and Moncrieff, 2001). It has been documented that in order to 

successfully assess the impacts of changing climate on ecosystem carbon fluxes it would be very 

necessary to understand the effects of temperature and moisture on Q10 which are of critical 

importance in any such assessment (Betts, 2000; Cox et al., 2000). Recently conducted studies 

have shown that seasonal values of Q10 are negatively correlated with temperature, but positively 

related to soil water content over a limited range of soil water content (Xu and Qi, 2001; 

Reichstein et al., 2002; Qi et al., 2002; Janssens and Pilegaard, 2003). Currently, when 

temperature and moisture effects on soil or ecosystem respiration are described simultaneously, 

e.g., using models of global climate change, assumptions are made to the effect that individual 

factors may be multiplicative (Fang and Moncrieff, 1999). This hypothesis has not been well 

tested and may lead to errors associated with an overestimation of the respiration response of 

ecosystem to warming under dry soil conditions (Cox et al., 2000; Reichstein et al., 2002). 

Unfortunately, applying different sensitivity values of soil or ecosystem respiration to 

temperature and moisture has not been explicitly looked at in the ecosystem models that are 

commonly used in the studies of global climate change. This has the potential of resulting in a 

significant missing link in the current ecosystem models (Qi et al., 2002). Simulating soil or 

ecosystem respiration without a sufficient understanding of variation in temperature sensitivity 

will certainly limit a model’s utility (Fang and Moncrieff, 2001; Qi et al., 2002). 

2.5 Moisture and soil organic matter turnover 

Temperature variation and that of precipitation act as the dominant factors controlling SOC 

cycling over global to regional scales (Jenny, 1980; Post et al., 1982). The overriding climatic 

control of SOC cycling in arid and semiarid ecosystems has to do with the timing and frequency 

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of precipitation. Water-limited ecosystems are typically characterised by a pulse-dynamic 

whereby sporadic precipitation events drive pulses of biological processes (Noy-Meir, 1973; 

Huxman et al., 2004; Schwinning and Sala, 2004). Therefore, the spatial pattern and close 

association of soil–litter interfaces are critical to controlling microbial access to nutrient 

resources during brief periods of soil moisture (Whitford et al., 1986). Given the projected major 

impact of climate change on water balance as a result of fluctuations in the distribution of 

precipitation and global warming (IPCC 2007), it is very necessary to understand how the 

interaction of temperature and moisture may influence SOM decomposition and C release from 

different soils. For example, it has been suggested that aerobic soil respiration is a non-linear 

function of temperature as long as soil water content does not limit the ecophysiological 

performance of microbes, but becomes a function of water content when soil dries out (Smith et 

al. 2003). 

Similarly, the effect of increased temperature on water tables has also been linked to dissolved 

organic carbon (DOC) rise (Freeman et al. 2001a; Evans et al. 2002; Pastor et al. 2003). 

Compared with areas receiving constant water, drier soils are expected to have higher turnover 

rates of SOM due to the favourable aerobic conditions for the heterotrophic and enzymatic 

activities. For example, lowering the water table increases peat aeration and consequently, 

removes the oxygen constraints on the activity of the phenol-oxidase enzyme, capable of 

degrading phenolic compounds (Freeman et al. 2001b). These substances are strong inhibitors of 

microbial and hydrolytic activities responsible for peat decomposition (Wetzel 1992) and 

therefore, their removal also eliminates the restrictions on the release of CO2 to the atmosphere 

and the subsequent movement of DOC to the rivers (Freeman et al. 2001a,b, 2004). Periods of 

little or no precipitation also influence soil water chemistry by promoting oxidation reactions 

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which result in pH reductions and increasing ionic strength (Adamson et al. 2001), both of which 

suppress DOC mobility. However, the lack of corresponding trends between hydrological 

changes and DOC increases indicates that finding the satisfactory mechanism remains a 

challenge. 

In addition, decreasing soil moisture at the top layers can induce the vertical migration of soil 

microorganisms such as enchytraeid worms (dominant mesofauna in peatlands) and 

consequently, accelerate C turnover in the deeper layers (e.g. Briones et al. 1998a, 2010). 

However, if water becomes severely restricted their populations become significantly reduced 

because most species lack an adaptive drought tolerant stage (Maraldo et al. 2008). Therefore, 

any alterations in these two abiotic factors and their influence on soil biota will be of key 

importance in determining the responses of SOM decomposition to climate change. 

2.6 Soil type and soil organic matter turnover 

Different soil types have been found to affect the growth as well as other processes and materials 

added to the soil. West Africa soils are fragile, predominantly of kaolinitic clay, with low 

effective cation exchange capacity (ECEC) and plant nutrients (Juo and Wilding, 1996). In 

addition tropical climate is characterised by high rainfall and insolation, the attendant problems 

of nutrient leaching and low level of soil organic matter which in some cases has made nitrogen 

(N) the most limiting nutrient to crop production in Nigeria (Carsky and Iwuafor, 1995). Young 

et al. (1998) emphasised the importance of the soil’s structure in maintaining biological diversity 

through the provision of habitat and by influencing patterns of resource storage and transport. 

Modern tools in analytical chemistry are forcing researchers to re-examine long held theories of 

soil organic matter formation. Hassink et al. (1997) have shown that the amount of organic 

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matter that a soil can store is largely regulated by its silt and clay content although management 

can also influence storage, particularly of larger macro-organic matter fractions (Balesdent et al., 

2000; Denef et al., 2001). Spatial variation of soil organic matter content particularly at national 

and regional scales are also strongly influenced by climate and land use (Joos et al., 2001; 

Paustian et al., 1998b). 

2.7 Effect of microorganisms on soil organic carbon 

Microbial populations in soil are of great importance due to their role in serving as an important 

reservoir of plant nutrients (Wardle, 1992), in addition to their ability to alter ecological 

processes (Smithwick et al., 2005). In order to understand the role that microbial communities 

play in different environments, it is very important to understand microbial functional diversity 

and its response to soil perturbations and climate warming (Lagomarsino et al., 2007; Rinnan et 

al., 2009). Both microbial biomass and community composition are sensitive to belowground 

profile which often correlates with the soil organic matter content (Aanderud et al., 2008; Fierer 

et al., 2003, Rajaniemi and Allison 2009). Research has shown that sites with lower fertility have 

lower soil microbial biomass compared to those with higher fertility (Mendham et al., 2003). 

However, microbial communities are also affected by different environmental variables such as 

soil salinity, or other factors which change during ecosystem development (Aanderud et al., 

2008; Rajaniemi and Allison 2009 and, Zornoza et al., 2009). 

The impact that earthworm invasion has on the stability of SOC is of great significance in 

biogeochemical studies with their overall effect on C dynamics being dependent on time scales 

(Martin, 1991), soil disturbances (Bohlen et al., 2004a and, Villenave et al., 1999), and SOC 

levels (Bohlen et al., 2004b). Several studies have shown that earthworm activity has the 

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potential of contributing to the stabilization of SOC through enhanced long-term protection by 

soil aggregates (Fonte et al., 2007; Pulleman et al., 2005; Scheu, and. Wolters, 1991, Tiunov, 

and. Scheu, 2000) and to a loss of unprotected C through increased short-term mineralization 

rates (Alban and Berry, 1994; Bohlen et al., 2004a, Coq et al. 2007, Martin, 1991). Therefore the 

relative significance of short-term mineralization and longer-term C protection may affect carbon 

cycling and the optimal management practices for tropical plantations. Coq et al. (2007) in a 

study noted that short-term (150 days) C mineralization enhancement was greater than long-term 

(420 days) C protection with P. corethrurus present. Bossuyt et al. (2004) in looking at 

earthworms also noted that their presence increased levels of macro- and micro-aggregates, thus 

enhancing long-term C incorporation in soils during a laboratory study, while other researchers 

found no changes in the size distribution of aggregates (Fonte et al., 2007 and Villenave et al., 

1999). 

Soil microbial biomass carbon (MBC) has been found to be an effective measurement used as an 

index to evaluate soil quality because it is sensitive and measurable, and it is related to global 

carbon cycle (Wardle, 1992), soil quality (Rice et al., 1996), soil C/N ratio (Smolander and 

Kitunen, 2002) and linkage of plants and soil (Hofman et al., 2004). Microbial biomass carbon is 

very much linked with soil organic carbon and soil carbon cycling (Follett, 1997). It has been 

found out that soil microbes utilise only labile organic carbon when SOC input is limited. After 

all labile organic carbon is fully utilized, soil microbial biomass then falls (Follett, 1997). The 

addition to the soil in the form of falling litter increase the amount of soil organic matter during 

forest ecosystem recovery, which may lead to increasing food resource for microbes and further 

increase microbe population as well. Therefore, soil MBC can indicate soil quality in the red soil 

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25 

region (Yu et al., 1999), and thus can be used to indicate the role of different vegetations on the 

reconstruction of the red soil ecosystems. 

Soil microbial entropy is another important indicator defined as the ratio of soil MBC to total 

organic carbon (TOC). It can be used to reflect the percentage of the soil active organic carbon in 

the soil, demonstrate the difference of soil fertility, monitor the efficiency of soil carbon, and 

reflect the change of soil environment (Anderson, 2003). It is also an important tool used to 

assess the soil carbon accumulation or loss in soil ecosystems. Higher index results in more 

accumulation of the soil carbon, or otherwise soil carbon loss (Singh et al., 1989). Thus, the 

variations in soil microbial entropy reflect organic matter inputs to soils, the efficiency of 

conversion to microbial C, losses of C from the soil, and stabilisation of organic C by soil 

mineral fractions. Also affecting this index is clay content, mineralogy, vegetation and 

management history of the soil (Sparling, 1992). It has also been proven that stores of carbon at 

depth are often more resistant to decomposition by soil microbes due to their inherent physical 

properties and chemical constituents (Fierer et al., 2003), and also due to the fact that recalcitrant 

soil fractions enriched with resistant alkyl carbon structures increase with soil depth and age 

(Lorenz et al., 2007). 

2.8 Soil carbon sequestration under forests and plantations 

Carbon sequestration in forest soils has a potential to decrease the rate of enrichment of 

atmospheric concentration of CO2. Increase in C stock of forest soils can be achieved through 

forest management including site preparation, fire management, afforestation, species 

management/selection, use of fertilisers and soil amendments (Lal, 2005). The SOC 

concentration in forest soils may range from 0% in very young soils to as much as 50% (w/w) in 

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some organic or wetland soils (Trettin and Jurgensen, 2003), with most soils containing between 

0.3 and 11.5% C in the surface 20 cm of mineral soil (Perry, 1994). According to Jones (1989) 

SOC concentration in mineral soils is lower in tropical forests and higher in montane and boreal 

forests. Knoepp and Swank (1997) studied the SOC dynamics in five watersheds in the southern 

Appalachian region and reported that the SOC and N concentrations generally declined during 

the first years following the whole tree harvest, but SOC remained stable 14 years after cutting. 

In California, Black and Harden (1995) also observed that timber harvest resulted in an initial 

loss of SOC (15%) within 1–7 years due to oxidation and erosion. For 17 years of forest re-

growth, there was a continued loss of SOC (another 15%) despite the slight accumulation of new 

litter and roots. After 80 years of re-growth, rates of C accumulation exceeded rates of loss. Over 

the 80-year period, the SOC stock did not recover to the pre-harvest level. In Oregon, Law et al. 

(2001) observed that SOC stock was consistently lower at all soil depths compared to pre-

disturbance conditions. 

Other studies have, however, shown that the observed post-harvesting decline in SOC is 

generally due to mixing and movement of the organic material or litter layer into the mineral soil 

(Yanai et al., 2003). Harvesting operations often cause drastic soil disturbance (Nyland, 2001) 

mixing the forest floor into the mineral soils. The exposure of the soil also exacerbates losses due 

to soil erosion (Elliot, 2003), and leaching of dissolved organic carbon (Kalbitz et al., 2000). 

Numerous studies have shown that decomposition rates of surface litter generally decrease after 

clear cutting because of the reduction in biotic activity and decrease in soil moisture content. 

Afforestation/reforestation and the manager’s choice of species are also important to enhancing 

soil C stock. Reforestation of abandoned/marginal agricultural lands can increase SOC stock 

(Akala and Lal, 2001). In northern Belgium, Schauvlieghe and Lust (1999) assessed C budgets 

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under different land use systems. The total C stock was 128 Mg/ha under pasture, 173 Mg/ha 

under 29-year-old forest and 232 Mg/ha under 69-year-old stand. The total C stock was 117 

Mg/ha under 27-year-old pin oak stand and 227 Mg/ha under 69-year-old oak beech stand. It was 

observed that the older the stand, the larger the importance of soil C became, especially the 

stable soil C. In east-central Minnesota, Johnston et al. (1996) reported an average increase in 

SOC stock at the rate of 0.8 Mg C ha-1year-1 in the mineral soil over a 40-year period due to 

afforestation of degraded agricultural soils. Afforestation of reclaimed mine soil, an important 

economic activity affecting deforestation, has a strong impact on SOC sequestration (Akala and 

Lal, 2000). 

Past and current studies of soil C sequestration during forest re-growth on previously cultivated 

agricultural soils have provided varying results. Post and Kwon (2000) reviewed 46 studies, and 

reported that soil C increased at an average rate of 0.34 Mg C ha-1 year-1, with a broad variation 

range between -0.5 and +0.7 Mg C ha-1 year-1. The study locations ranged from cool temperate to 

tropical and the forest ages ranged from 8 to >250 years old. Paul et al. (2002) also reviewed 

these estimates and computed an average rate of soil C sequestration of 0.14 Mg C ha-1 year-1. 

The highest rates of soil C accumulation were observed under deciduous or N-fixing species, 

established on previously cultivated land in tropical or subtropical regions. Estimated rates of 

soil C sequestration under intensively managed plantations ranged from 0 Mg C ha-1 year-1 under 

eucalyptus (Eucalyptus saligna Sm.) (Bashkin and Binkley, 1998) and hybrid poplar (Grigal and 

Berguson, 1998) to 1.6 Mg C ha-1 year-1 under other hybrid poplar plantations (Hansen, 1993). 

Hansen (1993) observed that fast-growing species (i.e., poplar) can significantly increase the soil 

C pool, after an initial C loss caused by site preparation. Twelve- to eighteen-year old poplar 

plantations had greater average soil C pool than adjacent soils cultivated to row crop or grassland 

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on 11 sites across North Dakota, Minnesota, Iowa, and Wisconsin. In a similar study under 6- to 

15-year-old poplar plantations, Grigal and Berguson (1998) estimated an input of 1.2 Mg C ha-1 

year-1 as root biomass into the soil, without detecting any overall significant increase in the soil 

C pool. Similarly in Hawaii, Bashkin and Binkley (1998) observed no overall increase in the soil 

C pool under 10- and 13-year old eucalyptus plantations (114 Mg C ha-1) compared to adjacent 

abandoned sugarcane fields (113 Mg C ha-1) in the 0- to 55-cm depth. Smitha et al., 2002 studied 

C stocks after conversion of forests into tree plantations and observed that there was no 

significant effect for stand type in surface soils when the C was determined under the tree 

plantations. Similarly, carbon stocks in the forest floor was not significant for stand type even 

though the C content in both cases were high. 

2.9 Carbon sequestration under a Chronosequence 

Sartori et al., (2007) in a Chronosequence experiment involving poplar observed that during 10 

years of plantation management and re-growth on eolian soils, the soil C pool tended to increase 

primarily because of management-induced C inputs in the 0-10-cm depth. Their study supports 

other similar research findings, indicating that it is not possible to observe measurable changes in 

the mineral soil C pool under poplar plantation compared to adjacent agricultural lands over a 

decadal time scale (Grigal and Berguson, 1998; Coleman et al., 2004). Also, Coleman et al. 

(2004) compared poplar stands of varying ages (from 1 to 12 years old) to adjacent agricultural 

lands and woodlots in 27 locations across Minnesota, Wisconsin, Iowa, and North Dakota and 

observed significant increases in soil C concentration compared to adjacent agricultural lands 

only in presence of soils with low-inherent C concentration. In general, there were no differences 

in soil C concentration between agricultural lands and poplar plantations. 

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Richards et al., 2007 studied carbon sequestration in native subtropical tree plantations by 

estimating rates of C input and loss after land use conversion to a hoop pine plantation 

Chronosequence (25–63 years) or pasture. They used the Century C model to split the slow 

turnover pool into an intermediate and a stable C pool, where it was observed that hoop pine C 

inputs to the more stable section were much lower than rainforest or pasture C inputs. Total C 

stocks only reached 16 t C ha-1 under the 63-year-old hoop-pine, compared to rainforest (37 t C 

ha-1) and pasture (31 t C ha-1). Interestingly, there was no difference in total light fraction (LF) C 

between older hoop pine plantations and rainforest, indicating that hoop pine plant biomass 

enters the LF soil C pool initially, but that the majority of these inputs are not further stabilized 

within the soil matrix. This may result from disruption or modification of the mechanisms 

responsible for SOC protection, such as aggregation and organo-mineral interactions (Baldock 

and Skjemstad, 2000). 

2.10 Carbon studies under oil palm in Africa 

In Africa, with special reference to West Africa some works have been done in Benin and Ivory 

Coast. Dufrêne and Saugier (1993) in Ivory Coast looked at photosynthetic measurements in oil 

palm which had results quite lower than that carried out by Lamade and Setiyo (1996) in North 

Sumatra. Jourdan (1995) also studied and modelled root growth under oil palm in Ivory Coast to 

assess the contribution of roots to CO2 emissions and C storage in soil. Similarly, soil respiration 

studies have been conducted by Lamade et al., (1996) at Ouidah (Benin), taking a look at 

ambient temperature of 27°C, which they claim led to an estimation of carbon loss through root 

respiration of 76 kg C yr–1 palm–1 in a 20-year-old plantation. On the other hand some studies 

(Ollagnier et al., 1978; Olivin, 1980; Djegui et al., 1992; Haron et al., 1998) under Ivorian 

conditions have also measured changes in soil carbon content from destruction of the forest 

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ecosystem to its replacement by an oil palm plantation. They observed that when such a 

replacement was made, there was a notable drop in soil carbon (in the upper horizons, 0-30 cm) 

in the first 4 years as the young oil palms develop, then that rate seems to stabilize from 9 years 

old onwards at between 55% and 65% of the previous forest soil content. 

2.11 Summary 

From the literature review, it is clear that even though the oil palm tree originated from Africa, 

there is not much information regarding its contribution to CO2 emissions into the atmosphere. 

There also appears not to be adequate information on C storage and dynamics under oil palm 

plantation in Ghana and other oil palm producing countries in West Africa. Much of the 

information currently available and used in scientific discussions has come from studies that 

have been undertaken elsewhere. It is important for oil palm growing countries in Africa to 

undertake research into the various contributions of oil palm to the environment and possibly 

come out with innovations that would be beneficial to maximising yield and at the same time 

protecting the environment. This has become necessary as companies involved in oil palm 

business appear to be shifting their focus from well known production areas such as Kalimantan, 

North Sumatra, Borneo, Indonesia and surrounding regions as a result of pressure from 

environmental pressure groups to Africa for possible expansion. This expansion would certainly 

affect current vegetation which would also have an overall effect on prevailing and future 

climate in Africa and the world. There is the need to come out with clear cut guidelines regarding 

the future of oil palm production in Ghana so that the country does not lose out in its bid to 

expand agriculture, increase revenue and improve livelihood of its nationals. This can only be 

done through government and private sector support for appropriate research into this sector. 

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CHAPTER THREE 

MATERIALS AND METHODS 

3.1 Site selection and description 

The sites chosen for the study were private oil palm plantations in and around Kade, Kusi, and 

Anwaem located within the Kwaebibirim District of the Eastern Region of Ghana. The reference 

soil, (uncultivated forest soil) was taken from the Forest and Horticultural Crops Research 

Centre, Okumaning within the same district (Fig3.1). The private oil palm plantations are owned 

by local farmers; some residents in these communities or in nearby towns. These farmers owned 

oil palm farms at different maturity ages from very young ones of about three months old to 

farms as old as twenty-six years. The farms were located on different points along the 

toposequence with some farms spreading right from the top to the bottom slope. The current 

palm trees standing on the land at the time of sampling are between two and a half years and 

twenty six years. 

3.1.1 Site selection 

Sampling of farms begun with creating five clusters according to age of oil palm plantation into 

which various farmers were grouped. During farm visits some questions were asked and farms 

that had any form of cover cropping were struck out of the list (Appendix C). Multi-stage 

sampling was employed to further group farms depending on position of farms along the 

toposequence into three distinct groups; Top slope, Middle slope and Bottom slope. Using modal 

instance sampling the research targeted farms located at the valley bottoms. Farms included in 

this list were chosen based on having similar land use history and cultural practices involved in 

oil palm plantation establishment. Eight farms were targeted under each age group so further 

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sampling could be carried out to select five. Having exhausted the original list of farmers and not 

getting the targeted number snow balling was carried out to get more farms for each of the age 

groups. In the end it was difficult to get even four farms for one of the age groups whiles some 

had about five and others six or seven. In the end three farms were selected for each age group. 

Random sampling was carried out in groups with more than three farms taken into consideration 

sampling costs and location. Fifteen farms in total were selected for sampling. In addition, a 

reference soil was chosen from the forest reserve (plot 16) having similar characteristics as soils 

from each of these farms (Appendix A). 

 

Fig. 3. 1 Location of farms territory and sampled plots. 

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3.1.2 Site description 

The vegetation of the district is largely semi-deciduous with perennial tree species such as cocoa, 

teak, mahogany, neem, bamboo, mango, orange and coconut interspersed. There are also grass 

species like Panicuum maximum, giant star grass, spear grass among others. 

3.1.3 Prevailing climate of Kwaebibirim district 

Present climatic conditions within the district are not different from those found within oil palm 

belts in Ghana and parts of West Africa. These include high rainfall and temperature, long 

sunshine duration, etc which play a key role in the growth and optimum yield of oil palm 

(Tweneboah, 2000). 

3.1.3.1 Rainfall 

The study site is marked with high rainfall usually between 1200 and 2200 mm with an average 

of about 2000 mm distributed fairly throughout the year. There are periods of slight dry season 

occurring between December and February due to the harmattan but no severe dry periods are 

recorded. Annually high intense rainfall usually occurs between May and early parts of 

September which are often in excess of plant evapotranspiration needs providing enough 

moisture needed for optimum yield production. Adequate rainfall is recorded for the remaining 

period of the year but in low amounts. The high precipitation accounts for erosion which is very 

common on exposed land surfaces. Tweneboah (2000) reported that an area suitable for oil palm 

production should have a long wet season with rainfall exceeding 180 mm and a short dry season 

usually not more than a month with rainfall of at least 100 mm. 

 

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3.1.3.2 Sunshine duration 

The photoperiod in the district varies depending on the time of the year. Usually the sun appears 

earlier than in other places since it is to the east of Ghana. During high rainfall months such as 

July and parts of August, sunshine hours is usually between five to six hours. However, towards 

the end of the year to early February longer sunshine hours of about eight to ten hours are 

experienced. These sunshine periods are characterised by high temperatures which support the 

establishment and productivity of oil palm in areas where they are grown such as Brazil, South-

East Asia, Malaysia and Indonesia as published by Tweneboah (2000). 

3.1.3.3 Temperature 

The long sunshine duration allows for high temperatures of about 28-34oC and low temperatures 

of about 22-24oC with an average of about 25-29oC. These temperatures are within the 

requirements for good oil palm production as has been reported by Tweneboah (2000). 

3.1.4 Soil description 

The sites selected were oil palm farms established at the valley bottom along a typical catena. 

The dominant soil at this location is Oda Soil Series which has been classified as Aeric 

Endoaquent (Owusu-Bennoah, 1997, USDA, 1998) and as Eutric Gleysol (FAO; 1998; WRB, 

1998). 

3.1.5 Sample collection and preparation 

The soils were sampled from a depth of 0-10 and 10-20 cm with the aid of an earth chisel after 

the land surface had been cleared using a cutlass. The 0-20 cm layer from the literature reviewed 

is the depth considered for many C studies due to root activity present in it. 

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Sampling was preceded by marking out an area 25m by 25m. These sampling plots contained 

both alleys between rows of palm trees and pruned and heaped palm fronds within the palm 

rows. A total of thirty six spots were marked in the alleys using short pegs for sampling. Heaps 

of prunnings of the palm fronds which fell within the marked area had samples taken under 

them. In all a total of 72 soil samples were taken from the alleys from 0-10 and 10-20 cm layers 

respectively. Core samplers were driven into the ground to take undisturbed soil samples within 

the alleys for bulk density analysis. Soil samples under the heaped fronds were carefully 

collected within the marked area using two methods. These methods depended on the age of the 

plantation. The first method involves taking soil samples from younger heaps (< 10 yrs) which 

had been pushed over whiles the second method involves taking soil samples after cutting 

through the huge prunnings (> 10 yrs) with a cutlass to get to the top soil. The soil samples under 

the heaped fronds were taking using the same procedure as that under alleys for both layers. 

Sampling under the prunnings was done carefully especially under old heaps since there was the 

need to distinguish the top layer from the decomposed material sitting just above it. 

Total number of heaps from which soil samples were taken were three per sampling site. 

Random soil samples were taken from the natural forest reserve. 

Soils sampled were packed into polythene bags, labelled and put into another polythene bag to 

prevent contamination. Soils from the sampled spots from each farm were put together to obtain 

a composite sample and a sub sample taken. Soils were air dried, crushed and sieved through a 2 

mm sieve to get rid of stones, roots, twigs and other unwanted materials. Processed soil samples 

were put in well labelled polythene bags before being packed into well labelled boxes for 

transportation to the laboratory for analyses. Soil samples were stored at room temperature and 

this was followed by analyses at the Department of Soil Science laboratory, University of Ghana. 

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3.2 Soil physical properties 

3.2.1 Bulk density (ρb) determination 

Bulk density was determined using the core method. A cylindrical metal core of known diameter 

and height was driven into the soil with the help of a mallet. The soil sample was taken out 

together with the ends of the metal core trimmed. The sample was taken to the laboratory for 

oven drying for 24 hrs at 105°C after which the dry weight was determined. The weight of the 

empty metal core was also taken. 

Bulk density was calculated using the formula (Blake and Hartge, 1986) 

ρb = M/V……………………………………………........……………………………(3.1) 

Where M= Mass of oven dried soil 

  V= Volume of soil in core sampler 

3.2.2 Particle size analysis 

Particle size analysis of the soil was done by the Bouyoucos hydrometer method modified by 

Day (1965). Forty grams of ground, air-dried soil screened through a 2 mm sieve was weighed 

into a polyethylene bottle and 100 mL of sodium hexametaphosphate (calgon) solution added to 

it and covered. The suspension was put into a mechanical shaker and shaken for 2 hrs after which 

the suspension was transferred into a sedimentation cylinder with distilled water and topped up 

to the 1000 mL mark. A plunger was lowered into the cylinder and moved up and down to mix 

the suspension thoroughly. This was left for about 5 mins after which the hydrometer was 

lowered into the suspension and the scale read at the top of the meniscus as the hydrometer 

reading for clay and silt. 

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The suspension was allowed to stand undisturbed and the hydrometer reading for clay alone was 

taken after 4 hrs 55 mins. After the second reading, the suspension was poured out directly into a 

50 mm sieve from the sedimentation cylinder with the affluent collected into a waste container. 

The residue on the sieve was agitated by running ordinary tap water into it to obtain the sand 

particle. This was transferred into a moisture can using a wash bottle and oven dried for about 24 

hrs at 105°C. The weight of sand was recorded. The percent sand, silt and clay were then 

determined by: 

% X= 
$	×&''

(��)*�	+�	,+�- … … … … … … … … … … … … … … … … … … … … �3.2� 

Where X= Weight of sand/ Readings for silt and clay 

3.3 Soil chemical properties 

3.3.1 Determination of pH water (1:1) 

Twenty grams of soil were weighed into a beaker and 20 mL of distilled water was added, to 

give a soil to water ratio of 1:1. The mixture was stirred several times for about 30 mins and left 

to stand for about 1 hr to allow most of the suspended clay particles to settle and also to attain the 

surrounding temperature of the instrument room. 

The glass electrode pH metre- CG818, Schott Great was standardised using two solutions of pH 

4 and 7. The electrode was then rinsed with distilled water and then immersed into the partly 

settled suspension with the reading on the pH meter recorded. This was done thrice and the mean 

value taken. 

 

 

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3.3.2 Determination of pH CaCl2 (1:2) 

Ten grams of soil were weighed into a beaker and 20 mL of CaCl2 solution was added, to give a 

soil to salt ratio of 1:2. The mixture was stirred several times for about 30 mins and left to stand 

for about 1 hr to allow most of the suspended clay to settle and also to attain the surrounding 

temperature of the instrument room. 

The glass electrode pH metre- CG818, Schott Great was standardised using two solutions of pH 

4 and 7. The electrode was then rinsed with distilled water and then immersed into the partly 

settled suspension with the reading on the pH meter recorded. This was done thrice and the mean 

value taken. 

3.3.3 Determination of organic carbon in the soil 

Organic carbon was determined using the wet oxidation method of Walkley and Black (1934). 

This method involves the reduction of Cr₂O₇²¯ ion by the organic matter and the unreduced 

Cr₂O₇²¯ measured by titration with Ammonium Ferrous Sulphate. The quantity of organic matter 

oxidised is calculated from the amount of Cr₂O₇²¯ reduced. 

One half of a gram of finely ground soils sieved through a (0.5mm) was weighed in triplicate 

into 500 mL Erlenmeyer flasks. Ten millilitres of 1.0 M (K₂Cr₂O₇) followed by 20 mL of 

concentrated H₂SO₄ were added to the soil. The flask was swirled making sure the solution was 

in contact with all particles of the soil and allowed to stand on asbestos sheets for about 30 

minutes. 

Then, 200 mL of distilled water was added and this was titrated against 0.5 M acidified 

Ammonium Ferrous sulphate. In the titration, 5 mL of 85% orthophosphoric (H₃PO₄) acid and 2 

mL of Barium diphenyl-4 sulphonate indicator was added before titrating against the Ammonium 

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Ferrous sulphate from an orange colour to a green end point. Organic matter content was 

calculated by multiplying percent organic carbon by the conventional factor of 1.33 using the 

formula 

 % OC = 
Volume of Cr2O7

2- used – (Titre value × Molarity of blank) × Meq C (0.3) × 1.33 × 100

Weight of soil	�g� … �3.3� 

3.3.4 Determination of total nitrogen in the soil 

Total Nitrogen was determined by a modified Kjeldahl digestion method (Bremner, 1960). The 

nitrogen in the sample was converted to ammonia by digestion with concentrated H₂SO₄ using a 

nitrogen catalyst (Selenium tablet). The ammonium formed was determined by distillation of the 

digest with an alkali and titrating with a standard acid. 

Air-dried soil of 2 g was weighed in triplicate into a Kjeldahl flask and a 2-3 mL of distilled 

water added to moisten the soil. The nitrogen catalyst was added followed by 20 mL of 

concentrated H₂SO₄. The mixture was digested for at least 30 mins till it became clear. The 

digest was allowed to cool, transferred with distilled water into a 100 mL volumetric flask, and 

made up to the volume. Five millilitres aliquot was pipetted into a Markham distillation 

apparatus and 5 mL of 40% NaOH added and rinsed to about 100 mL. Five millilitres of 20% 

Boric acid and a few drops of a mixed indicator (0.13 g of methyl red plus 0.666 g of methylene 

blue dissolved in 100 mL of 95% ethanol) were put into a conical flask. The distillation process 

was set up to titrate to trap NH₃ gas which appeared light green at endpoint. This was back 

titrated against 0.01 M HCl from green to purple endpoint. From the results, the percent Nitrogen 

in the soil was calculated by 

 % N= 
Titre value × Molarity of acid × Volume  of extract ×	N	factor	× 100

Volume	of	aliquot × Weight of soil	�g� … … … … … … �3.4� 

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3.3.5 Determination of exchangeable bases 

3.3.5.1 Extraction of exchangeable bases 

Ten (10) grams of soil was weighed into an extraction bottle and 100 mL of 1M ammonium 

acetate solution (NH4OAc) buffered at pH 7.0 added. The bottle and its contents were placed on 

a mechanical shaker and shaken for an hour after which it was centrifuged for 20 mins. The 

supernatant solution was then filtered through a No. 42 Whatman filter paper. The filtered 

solutions (aliquot) were used for the determination of Ca, Mg, K and Na. 

3.3.5.2 Determination of exchangeable calcium 

To a 10mL aliquot of the sample solution, 10mL of 10% KOH and 1mL triethanolamine (TEA) 

were added. Three drops of 1M KCN solution and a few crystals of cal-red indicator were then 

added after which the mixture was titrated against 0.02N EDTA solution from red to blue end 

point. The titre value was used in the calculation of calcium as shown below.  

Ca (Cmol/Kg) = 
Titre value × Molarity of EDTA × vol.  of extract × 100

Volume	of	aliquot × Weight of soil	�g� … … … . … … . … �3.5� 

3.3.5.3 Determination of exchangeable magnesium 

To a 10mL aliquot of the sample solution, 5mL of ammonium chloride – ammonium hydroxide 

buffer solution was added followed by 1mL of triethanolamine. Three drops of 1M KCN 

solution and a few drops of Eriochrome black T solution was then added after which the mixture 

was titrated with 0.02N EDTA solution from red to blue end point. This end point titre value 

determines the amount of calcium and magnesium in the solution. The titre value of magnesium 

was then de