The Role of Above-ground Biomass in Soil Fertility Management in Cocoa Plantations in Ondo State, Nigeria.

Transcription

1 From the SelectedWorks of Abuja Journal of Geography and Development Winter January 4, 2016 The Role of Above-ground Biomass in Soil Fertility Management in Cocoa Plantations in Ondo State, Nigeria. Afolayan, OS Geography and Environmental Management Department, University of Ilorin, Nigeria This work is licensed under a Creative Commons CC_BY International License. Available at: abujajournalofgeographyanddevelopment_geographyandenvironmentalmanagementdepartment/12/

2 The Role of Above-ground Biomass in Soil Fertility Management in Cocoa Abstract Plantations in Ondo State, Nigeria. Afolayan, O.S. Department of Geography and Environmental Management, Faculty of Social Sciences, P.M.B University of Ilorin, Nigeria Survival of cocoa in tropical rainforest is saddled with the sequential circulation and concentration of nutrient between the above and below-ground biomass. Prominent among the above-ground biomass is litter of which the accumulated nutrient in leaves return into the soil. Ability of cocoa tree to remain productive for quiet a number of years without the application of chemical fertilizer lies on the role of litterfall in returning nutrient already uptaken back to the soil. This paper assessed the aboveground biomass potential in soil fertility under cocoa plantations. A community from Idanre, Owo and Odigbo were purposively selected where matured cocoa farms within age 45 and 50 years were chosen. Leave litters and soil samples (topsoil and subsoil) were collected from each of the 25m by 25m quadrat. Both samples were subjected to physico-chemical analyses, using routine laboratory techniques. ANOVA result shows significant variation within the study area and Student t-test indicates significant difference between the above and belowground biomass. It was observed that the ability of litter to replenish lost nutrient from the soil is high when its nutrient content is considered in terms of P, Mg 2+, Ca 2+ and Mn in aged cocoa plantations. The study recommends seasonal relocation of pod deposit, periodic application of micronutrient via agrochemical and spreading of podhusk across the farms as well as adoption of pod husk fertilizer; to complement the effort of litter. Keywords: Litterfall, leaf, nutrient, soil, plantations. Introduction Biomass is a biological material derived from living, or recently living organism. According to the U.S Department of Environment (2005), It is any organic matter that is renewable over time. Biomass according to Susan (2004) is the total mass of all the organisms inhabiting a given area, or of a particular population or trophic level. Woody biomass is the accumulated mass, above and below-ground, of the roots, wood, bark, and leaves of living and dead woody shrubs and trees (U.S. Department of Agriculture, 2005). Nutrients in the yield are a fraction of the nutrients immobilized in the above- and below-ground biomass. Also, large amounts of nutrients are accumulated in the above-ground biomass although there are differences among the species. According to Hartemink (2003), aboveground biomass in forest plantations can be very high and reach up to Mg/ha Department of Geography and Environmental Management, University of Abuja, Nigeria. 1

3 after 20 years. Considered relevant among the above-ground biomass in soil fertility is litterfall. The major components of nutrient cycling in cocoa plantation are litterfall, throughfall and stemflow, decomposition, root turnover and nutrient immobilization. In cocoa ecosystem, nutrients are transferred through litter, rain wash and fine-root turnover. Litterfall can be subdivided into the litter from cocoa and shade trees which includes branches, twigs, leaves, fruits, and flowers. In many parts of the world, cocoa is produced under natural or planted shade tree. Shade trees compete for growth resources but may also ameliorate adverse climate conditions; reduce soil erosion, pests, and diseases; and increase nutrient use efficiency in cocoa (Beer et al., 1998; Hartemink, 2005). Litterfall is significantly low in nutrient concentration when compared to the fresh leaves as nutrients are reabsorbed before the leaves fall. However, nutrient concentration in litterfall is the function of season, species, soil fertility and surface configuration. The amount of nutrients annually transferred depends on the amount of litterfall and the nutrient concentration in the litterfall. Mere examination of soil property in cocoa plantation may not reveal the details of soil fertility without the involvement of leaf, litter and output (bean and pod) channel. According to Robert (1996), nutrient concentration in leaves serves as index of the influence of soil fertility since all leaves have the basic function and all use the same nutrients in photosynthesis and construction of organic materials. Similarly, Fred and Harold (2009) state that soil tests are the most common means of assessing fertility needs of crops, but plant tissue tests are especially useful for nutrient management of perennial crops. The litterfall has a vital role in recycling of nutrients since the nutrient accumulation through litter inputs frequency exceeds input from inorganic fertilizers in crops like cocoa which has a lot of foliage, synchronized flushing, and abundant litter fall either due to natural senescene or pruning. It was stressed that leaf litter may not be sufficient to replace the lost nutrient from cocoa plantation (Aikpokpodion, 2010). Inability of leaf litter to replenish lost nutrient in cocoa ecosystem may only be applicable to old cocoa plantations, especially those above 25 years of productive age. Throughfall and litterfall constitute the most important nutrient recycling processes in the cocoa ecosystem, which appears to be self-sufficient in terms of its nutrient requirement (de Oliveira and Valle, 1982). As the rate of nutrient removal slightly varies in cocoa species, the dynamics of returning them back to the soil must be definitely different. However, the lower the nutrient returns, the faster the loss of soil fertility and vice versa. Studies indicate that hybrid species grow and develop faster than local breed and the rate of returning the extracted nutrient for development is inversely proportional to the growth rate. Single species tree plantation immobilized soil nutrient faster and return less nutrient to the soil than native forest (Aweto, 2001). This study is therefore focused on the role and Department of Geography and Environmental Management, University of Abuja, Nigeria. 2

4 capability of above-ground biomass in soil fertility management in old cocoa plantations in Southwest Agroecological Zone of Nigeria. Study Area Ondo State is located in south-western Nigeria approximately between latitudes ' and 'N and longitudes ' and 'E. The state is bounded in the east by Edo and Delta States; in the west by Ogun and Osun States; in the north by Ekiti and Kogi States; and in the south by the Bight of Benin and Atlantic Ocean. The State covers an area of 15,820 sq km 2. The climate of Ondo State is of the lowland tropical rain forest type, with distinct wet and dry seasons. The rainy season commences from April to October with slight dry season between November and March. In the south, rain falls throughout the year with mean annual rainfall exceeding 2000 mm, but the three months of November - January may be relatively dry. The study area has the mean monthly temperature of 27 C with a mean monthly range of 2 C, while mean relative humidity is over 70%. However, in the northern part of the state, the mean monthly temperature and its range are about 30 C and 6 C respectively. Ondo State vegetation is classified under rainforest agroecological zone, an ideal belt for the production of tree crops. Ondo State soil is characterized by very deep and well-drained; loam sandy surface, sandy clay and clay loamy subsoil (Ajayi et al., 2010; Afolayan, 2015). The southern part of the state is characterized by sedimentary rock in the south and basement complex rock in the north (Daramola et al., 2009). Figure: 1 Ondo State showing Idanre, Owo and Odigbo Local Government Areas Sources: Modified from Ajibade and Afolayan (2014) Department of Geography and Environmental Management, University of Abuja, Nigeria. 3

5 Materials and Methods Three (3) of the existing eighteen (18) Local Government Areas (LGAs) in Ondo State namely Idanre, Owo and Odigbo were purposively selected for the study. From each of these, one (1) settlement was selected based on their annual rate of cocoa production over the years. The settlements were Alade, Ijeguma and Oniparaga respectively. Selected plantations range from years of age. From 25m by 25m quadrat selected in cocoa farms, twelve (12) soil samples were randomly taken from two different depths 0-15cm and 15-30cm considered as topsoil and subsoil respectively. The sampling was limited to this zone due to the fact that the most feeding roots of cocoa are concentrated in that depth (de Oliveira and Valle, 1990; Aikpokpodion, 2010). Cocoa fresh leaves, litters, beans and pods were considered as plant samples, at the same time regarded as above-ground biomass. Soil and plant samples were analysed for the same physico-chemical parameters using standard laboratory techniques at Step-B Central Research Laboratory, Federal University of Technology, Akure. Soil ph was determined potentiometrically in 0.01M calcium chloride solution ratio of 1:2 according to Peech (1965). Organic carbon was determined using the chromic acid digestion method (Walkley and Black, 1934). After ash and digestion of soil sample with 5ml of nitric acid (HN03) exchangeable cations which include calcium (Ca 2+ ), potassium (K + ), magnesium (Mg 2+ ) and sodium (Na + ) were determined with the aid of Atomic Absorption Spectrophotometer (AAS). Total nitrogen (N) was extracted with Bray-P solution according to Kjedahl Method (Bremmer, 1996). Extractable trace elements (Zn, Cu, Fe and Mn) were digested and measured after extraction with 0.02M using EDTA Atomic Absorption Spectrophotometer according to Isaac and Korber (1971). Laboratory results were subjected to descriptive and inferential statistics. Average mean and percentage were used to estimate the concentration of nutrient while ANOVA and Student s t-test were used to estimate the differences between the above and below biomass and variation within both biomass across the selected study areas. Results and Discussion Considered as above-ground biomass in this study are cocoa leaf, bean, podhusk and litter and below-ground are topsoil and subsoil (Table 1-3). Based on the nutrient compartment and mineral cycle in tropical rainforest, biomass accounts for the larger part of the nutrient in tropical rainforest ecosystem. The bulk of nutrients in tropical raiforests are stored in the living vegetation. According to Aweto (1989), mature tropical rainforest ecosystem have a large biomass which not only affords the ground adequate cover but also acts as a huge reservoir of nutrients, thereby preventing them from being leached away from the soil-vegetation system. The order of nutrient concentration in tropical rainforest ecosystem are biomass, soil and litter (Gersmehl, 1979). Relevant among the Department of Geography and Environmental Management, University of Abuja, Nigeria. 4

6 above-ground biomass is litter due to its nutrient replenishment ability in cocoa ecosystem while bean and podhusk are nutrients output loss channels. Litterfall is a fundamental process in nutrient cycling and it is the main means of transfer of organic matter and mineral element from vegetation to the soil surface (Vitousek and Sanford, 1986; Oladoye et al., 2008). Considerably, higher among the nutrient were the major essential nutrient except N in above-ground than below-ground biomass. Comparative analysis of the nutrient storage in biomass shows that N from macronutrient and most of the micronutrient especially Fe 2+, Cu 2+, Zn exceed above-ground biomass (Table 1-3). All chemical properties were higher in above than below-ground biomass especially cations (K +, Mg 2+, Ca 2+, Na + ) as well as P. In other hand, micronutrients with the exception of Mn were higher in the belowground biomass. This may be attributed to the nutrient deposit from the aerial parts of the biomass via throughflow, stemflow and litterfall due to heavy rainfall. Presence of N in the soil above the available quantity in the soil may be linked to the mobility impact of nitrate N (N03 - ). Average concentration of N in the soil ranges from 0.61 to 0.67% while its quantity in the above-ground biomass is 0.31 to 0.35% respectively (Table 1-3). Nitrogen in the annual litterfall is about 20 to 45% of the total N in the vegetation and 2 to 3% of the total N in the soil (Hartemink, 2005). Therefore, results across the tables show that litter has great capability to replenish some of the lost essential nutrients (P, Mg 2+, Ca 2+ ) and Mn) conveniently back into the soil in cocoa ecosystem. Availability of Mg 2+ higher in above-ground biomass in this study and its capability to replenish the lost nutrient in cocoa ecosystem, especially in cocoa producing areas of Ondo State is contrary to low Mg 2+ content observed by Ipinmoriti et al. (2009) in Ibadan. Also, Aikpokpodion (2010) opined that leaf litter may not be sufficient to replace the lost nutrients. Disparity in results may be linked to the differences in the examined crop species, spatial location, soil, and season. Due to nutrient mobility, plant species, soil nature, seasonality and farm management practice, concentration of nutrient vary from plant to soil and topsoil to subsoil as well. Plant species for instance, can potentially influence nutrient cycling in various ways, from differences in uptake, loss, litter quality and association with microbes (Sarah, 1992). It was observed that those plants that grow on nutrient poor soils produce recalcitrant litter with slow decomposition rate, conversely, those on fertile soil produce easily degraded litter according to Sarah (1992). A large part of the P in a cocoa ecosystem is found in the vegetation and in the litter whereas the amount in the soil is low. This show that nutrient with higher concentration in the litterfall is able to supplement loss nutrient from the soil. Large amounts of nutrients are returned to the soil with the litterfall (Hartemink, 2005). Nutrient concentrations in the litterfalls are lower than fresh leaves as nutrients are reabsorbed before the leaves fall. In cocoa ecosystem, podhusk is regarded as a waste, invariably Department of Geography and Environmental Management, University of Abuja, Nigeria. 5

7 considered as nutrient output in conjunction with yield harvest. Studies show that most of the micronutrients are immobile in soil. N, P, K + and Mg 2+ are very mobile in plant. It can be categorically emphasized from the result that cocoa pod accounts for more than half of K + loss in cocoa ecosystem. Finding from Adu-Dapach et al. (1994) in Ghana shows that Cocoa Pod Husk Ash was an effective source of K + for increasing grain yield of maize. It was also discovered by Odedina et al. (2003) that Cocoa Pod Husk Ash had higher concentration of N, K + and Ca than rice bran and wood. Concentration of nutrient in plant either above or below-ground biomass is strictly determined by the mobility factor of the nutrient. Some nutrient mobility in the soil and plant are limited. For instance, Nitrate nitrogen, sulfate sulfur and boron are very mobile in the soil while organic nitrogen, P, Cu 2+, Fe, Mn and Zn are immobile. Hence, most of the micronutrients are immobile in soil. In plant, N, P, K+ and Mg 2+ are very mobile while B and Ca 2+ are immobile. Mobility of this nutrient may also be influenced by the variety of the plants under consideration. Apart from nutrient mobility, availability of micronutrient in the soil compare to the plant parts may be linked to the seasonal application of diseases and pests controlled chemicals. This results to the nutrient storage variability in cocoa ecosystem (Table 3). The order of nutrient concentration in cocoa ecosystem compartment are as follows LF > PB > L > S. According to Mafongoya et al. (1998); Schroth (2003), several chemical characteristics of biomass affect the decomposition dynamics, especially their lignin and polyphenol content. Organic materials especially leaves, emanating from kola appear to decompose faster than those emanating from cocoa because cocoa leaves are lignified, hence cocoa leaves decompose very slowly (Ekanade, 1987; Ekanade and Egbe, 1990). Long-term productive year of cocoa without the application of chemical fertilizer is directly linked to the complementary roles of the litter in replacing lost nutrient especially via yield harvest. Table 1: Plant and Soil Properties in Above and Below-ground in Idanre Above-ground Below-ground Properties Bean Podhusk Litter Leaf Mean Topsoil Subsoil Mean ph OM (%) OC (%) N (%) K + (cmo1/kg) Mg 2+ (cmo1/kg) Ca 2+ (cmo1/kg) Na + (cmo1/kg) P (mg/kg) Fe 2+ (mg/kg) Cu 2+ (mg/kg) Zn (mg/kg) Mn (mg/kg) Department of Geography and Environmental Management, University of Abuja, Nigeria. 6

8 Source: Author s Fieldwork and Data Analysis (2015). Table 2: Plant and Soil Properties in Above and Below-ground in Owo Above-ground Below-ground Properties Bean Podhusk Litter Leaf Mean Topsoil Subsoil Mean ph OM (%) OC (%) N (%) K + (cmo1/kg) Mg 2+ (cmo1/kg) Ca 2+ (cmo1/kg) Na + (cmo1/kg) P (mg/kg) Fe 2+ (mg/kg) Cu 2+ (mg/kg) Zn (mg/kg) Mn (mg/kg) Source: Author s Fieldwork and Data Analysis (2015) Table 3: Plant and Soil Properties in Above and Below-ground Biomass Odigbo Above-ground Below-ground Properties Beans Podhusk Litter Leaf Mean Topsoil Subsoil Mean ph OC (%) OM (%) N (%) K + (cmo1/kg) Ca 2+ (cmo1/kg) Mg 2+ (cmo1/kg) Na + (cmo1/kg) P (mg/kg) Zn (mg/kg) Fe 2+ (mg/kg) Cu 2+ (mg/kg) Mn (mg/kg) Source: Author s Fieldwork and Data Analysis, 2015 Results show that there were significant differences in the average values of the examined physico-chemical in above and below-ground biomass with P-values of and respectively (Table 4 & 5). Similarly, in order to investigate the difference between the nutrient storage in above- and below-ground biomass, data on physico-chemical parameters were subjected to Student t-test. Department of Geography and Environmental Management, University of Abuja, Nigeria. 7

9 Table 4: Analysis of Variance on Above-ground Biomass in Cocoa Ecosystem Above-ground Sum of Squares df Mean Square F Sig. Between Groups Within Groups Total Source: Author s Data Analysis, 2015 Table 5: Analysis of Variance on Below-ground Biomass in Cocoa Ecosystem Below-ground Sum of Squares df Mean Square F Sig. Between Groups Within Groups Total Source: Author s Data Analysis, 2015 Table 6: Stuent t-test on Above and below-ground Biomass in Cocoa Ecosystem Test Value = 0 t df Sig. (2-tailed) Mean Difference 95% Confidence Interval of the Difference Lower Below-ground Above-ground Source: Author s Data Analysis, 2015 Upper Result shows that there is significant and statistical (tvc = 1.697) difference between both in terms of nutrient concentration (Table 6). Mean differences of above-ground compared to 1.84 below-ground biomass (Table 5) indicates high concentration of nutrient in above-ground biomass. Conclusion and Recommendations Litterfall has been identified as pathway of nutrient uptake back into the soil in cocoa plantation. Potential of litter to improve soil fertility in micronutrient is very low except Mn. This may be attributed to their immobility in plant. When compared Mn soil critical level of 1.0 mg -1, examined farms were less and not adequate but high in leaf and litter. However, considering the litter potential in soil fertility from point of view, the examined farms were all below the critical level of 25 mgkg -1 (Mn), 8mgkg -1 (Cu) and 4.5mgkg -1 (Fe) according to McKenzie (2001), yet, some are still above the quantity available in the soil. This may be attributed to their high quantity in herbicide, fungicide and insecticide Department of Geography and Environmental Management, University of Abuja, Nigeria. 8

10 periodically applied in cocoa farm and their immobility in the soil. In summary, ability of litter to replenish lost nutrient from the soil is high when its nutrient concentration is considered in terms of P, Mg 2+, Ca 2+ and Mn in both varieties. Therefore, ability of cocoa tree to remains productive more than 25 years stipulated by ICCO (2013) lies on the impact of essential nutrient concentration in the litter. Results show that the concentration of nutrient were higher in fresh leaf than the litterfall with less degree of association in the former compared to the latter. Finding from this study indicates that most of the essential macronutrient returns back to the soil through indigenous litterfall. It was observed that low return of the essential nutrient could be attributed to the large quantity seasonally stocked in podhusk and beans as well as immobilized in tree parts such as stem, twig, back and root. Based on the findings, the study recommends seasonal relocation of pod deposit and spreading of podhusk across the farm as well as adoption of pod husk fertilizer and application of micronutrient in conjuction with chemical applied; to complement the effort of litter. References Adu-Dapach, H.K., Cobbina, J. and Asare, E.O. (1994). Effect of Cocoa Pod Ash on the Growth of Maize. Journal of Agricultural Science, 122, Afolayan, O.S. (2015). Comparative Analysis of Nutrient Status in Indigenous and Hybrid Cocoa Plantations in Tropical High Forest Zone of Nigeria. Unpublished Ph.D. Thesis, Department of Geography and Environmental Management, University of Ilorin, Nigeria. Ajayi, I.R, Afolabi, M.O, Ogunbodede, E.F. and Sunday, A.G. (2010). Modelling Rainfall as a Constraining Factor for Cocoa Yield in Ondo State. American Journal of Scientific and Industrial Research, 1(2): Ajibade, L.T. and Afolayan, O.S. (2014). Comparative Analysis of Soil Nutrient Degradation in Hybrid and Indigenous Cocoa Plantations in Southwest Nigeria. Zaria Geographers, 21, Aikpokpodion, P.E. (2010). Nutrient Dynamics in Cocoa Soils, Leaf and Beans in Ondo State, Nigeria. Journal of Agricultural Science, 1(1):1-9. Aweto, A.O. (1989). Biogeography. Ibadan External Studies Series, p. Aweto, A.O. (2001). Impact of Single Species Tree Plantations on Nutrient Cycling in West African Rainforest and Savanna Ecosystems. International Journal of Sustainable Development, 8, Beer, J., Muschler, R., Kass, D. and Somarriba, E. (1998). Shade Management in and Cocoa Plantations. Agroforestry System, 38, Black, C.A. (1965). Methods of Soil Analysis ll. American Society of Agronomy, WI. Coffee Madison, Department of Geography and Environmental Management, University of Abuja, Nigeria. 9

11 Bremner, J.M. (1965). Total Nitrogen. In C.A. Black (ed.) Methods of Soil Analysis. Part 2. America Society of Agronomy, Madison Daramola, J.O. Adekunle, M.F., Olaniyi, M.O., and Alayanku, F.M. (2009). Diagnostic Survey Report of Ondo State Agricultural Production. Institute of Food Security, Environmental Resources and Agricultural Research. de Oliveira, L.J. and Valle, R.R. (1990). Nutrient Cycling in the Cacao Ecosystem: Rain and Throughfall Sources for the Soil and the Cacao Tree. Agriculture, Ecosystem and Environment, 32, Egbe, N.E., Ayodele, E. A. and Obatolu, C.R. (1989). Soil and Nutrition of Cocoa, Coffee, Kola, Cashew and Tea. Progress in Tree Crop Research in Nigeria, 2, Ekanade, O. (1987). Spatio-temporal Variation of Soil Properties under Cocoa Interplanted with Kola in a Part of the Nigeria Cocoa Belt. Agroforest System, 5, Ekanade, O. and Egbe, N.E. (1990). An Analytical Assessment of Agroforestry Practices Resulting from Interplanting Cocoa and Kola on Soil Properties in South-Western Nigeria. Agricultural, Ecosystems and Environment, 30, Fred, M. and Harold, V. (2009). Building Soil for Better Crops: Sustainable Soil Management, (3 rd Ed.) SARE Publisher, U.S.A. Hartemink, A.E. (2005). Nutrient Stocks, Nutrient Cycling and Soil Changes in Cocoa Ecosystems: A Review. Advance in Agronomy, 6, Hartemink, A.E. (2003). Soil Fertility Decline in the Tropics: With Case Studies on Plantations. ISRIC-CABI Publishing, Wallingford. Ipinmoroti, R.R., Aikpokpodion, P.E., Akanbi, O. (2009). Nutritional Assessment of Cocoa Plots for Soil Fertility Management on some Cocoa Farms in Nigeria. 16 th International Cocoa Conference, Indonesia (In press) Isaac, A.R. and Korber, J.D. (1971). Atomic Absorption and Flame Photometry; Techniques and Issues in soil, Plant and Water Analysis. In Saish, I.M. (Ed.) Instrumental Methods for Analysis of Soil and Plant Issues. Soil Sciences Society of America Publication Inc., Madison. Mafongoya, P.L., Giller, K.E. and Palm, C.A. (1998). Decomposition and Nitrogen Release Patterns of Tree Prunings and Litter. Agroforestry Systems, 38, McKenzie, R.H. (2001). Micronutrient Requirement of Crops. Alberta Agriculture and Rural Development. Accessed on 20 th November, 2013 Odedina, S.A., Odedina, J.N., Ayeni, S.O., Adeyeye, S.D., Arowojolu, S.A. and Ojeniyi, S.A. (2003). Effect of Types of Ash on Soil Fertility Nutrient Availability and Yield of Tomato and Pepper. Nigerian Journal of Soil Science, 13, Oladoye. A.O., Ola-Adams, B.A., Adedire, M.O and Agboola, D.A. (2008). Nutrient Dynamics and Litter Decomposition in Leucaena leucocephala (Lam.) De Wit Plantation in the Nigerian Derived Savannah. West African Journal of Applied Ecology, 13, 1-9. Department of Geography and Environmental Management, University of Abuja, Nigeria. 10

12 Peech, M. (1965). Hydrogen ion Acididty: In C.A. Black (Ed.), Methods of Soil Analysis, 2 Robert, L.S. (1996). Ecology and Field Biology. (5 th Ed.). Harper Collins College Publishers, U.S.A. Sarah, E.H. (1992). Effect of Plant Species on Nutrient Cycling. Tree, 7(10): Susan, M. (2004). Oxford Dictionary of Geography, (3 rd Ed.). Schroth, G. and Sinclair, F.L. (2003). Trees, Crops and Soil Fertility. CABI, Wallingfold. U.S Department of Environment and Department of Agriculture. (2005). Woody Biomass Desk Guide and Toolkit, p Thong, K.C. and Ng, W. L. (1978). Growth and Nutrient Composition of Mono-crop Cocoa Plants on Inland Malaysia Soil. In: Proceeding International Conference on Cocoa and Coconuts, Kuala Lumpur p Vitousek, P.M and Sanford, R.L. (1986): Nutrient Cycling in Moist Tropical Forest. Annual Review Ecology System, 17, Young, A. (1997): Agroforestry for Soil Management, (2 nd Ed.) CABI, Wallingford. Department of Geography and Environmental Management, University of Abuja, Nigeria. 11