SOIL-PLANT PROPERTIES DEGRADATION IN AGED COCOA FARMS IN SOUTHWEST NIGERIA

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1 SOIL-PLANT PROPERTIES DEGRADATION IN AGED COCOA FARMS IN SOUTHWEST NIGERIA ABSTRACT Afolayan, O. S. Department of Geography and Environmental Management, Faculty of Social Sciences, University of Ilorin, PMB Ilorin, Nigeria Nutrient stability in old cocoa farm requires sequence interaction and flow between soil and plant. Also, nutrient status in grown crop and other above-ground biomass depends wholly on the available nutrient in the soil. The study examined the nutrient status in soil-plant chemical properties in old cocoa farms of about 55 years of age. Laboratory results on soil and plants variables were subjected to multivariate analysis; multiple regressions, Student T-test, and Analysis of Variance. Result shows high efficiency of litterfall in Idanre and Odigbo. However, fresh leaf required high nutrient for development in Owo and Odigbo compared to Idanre while possibility of rapid soil nutrient degradation seemed to be prevalent in Owo compared to other location due to nutrients stocked in bean and podhusk. The study hereby recommends spatial integration of shade trees, seasonal spreading of accumulated podhusk to compliment litter nutrient input, and replacement of unproductive cocoa tree stands on annual basis. Keywords: Multivariate, nutrient, soil, plant, variable. INTRODUCTION Exchange of nutrients between the soil and plant variables in cocoa plantation can be sequentially linked to the economics principle of demand and supply. The higher the demand for the nutrient by plant variables (fresh leaf, pod, bean and others) the lower the concentration of such nutrients in the soil and vice versa. Soil nutrients reduced drastically during the growing and yield formative period. Nutrient interaction and relationship between tree crop and soil is best explained via nutrient circulation in cocoa ecosystem in tropical high forest zone. As a result of many years of nutrient mining from the ecosystem via annual yield harvest, there set in diminishing in soil-nutrient content. Apart from that, there are different factors that contribute to the degradation of soil-plant nutrient in old cocoa ecosystem. The growth and development of tree plant is the function of soil quality and quantity, plant species, management strategies and farm location. Distribution of plant species are both a cause and an effect on patterns of nutrient cycling in natural ecosystems. As with nutrient uptake and use species reinforce patterns of nutrient availability because those that grow on nutrient poor soils produce recalcitrant litter that decomposes slowly, whereas those that occur on fertile soil produce easily degraded litter (Sarah, 1992). Even within the specified region, there exist variations in soil-plant variation and interaction in terms of nutrient cycling. Plant species can potentially affect nutrient cycling in variety of ways, from difference in uptake, loss, litter quality, and associations with microbes, to differences in effects on herbivores (Sarah, 1992). In general, plant species characteristics create positive feedbacks to patterns of nutrient cycling. Species from environments where soil nutrients are abundant allocate more to above ground parts, have more rapid growth rates, and have higher rates of nutrient uptake per gram of root biomass than species from low nutrient environments (Sani and Jibril, 2010). Afolayan (2015), attributed the excess of essential nutrient in indigenous than hybrid litter to the large quantity annually stocked in the hybrid cocoa bean, podhusk and plant parts. Cocoa bean is the most prominent among the above-ground biomass that uptake enormous nutrient from the soil. Aboveground biomass in this context includes cocoa fresh leaf, litterfall, bean and podhusk. Nutrients in fresh leaf, pod husk and cocoa bean however, usually depend on the available nutrients in the soil. Nutrient concentration in leaves according to Robert (1996) serves as an 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. Therefore, it can be deduced that the nutrient return from vegetation to the soil depends on the nutrient uptake by the plant parts (Ajibade and Afolayan, 2014). Average yield of 1000 kg ha- 1 yr- 1 of dry cocoa beans removed 38, 6 and 77 kg of nitrogen, phosphorus and potassium respectively (Omotoso, 1975). Cocoa bean has an estimated contribution of 38%, podhusk, 16.3% and leaf, 1.3% to soil degradation in old cocoa farm in southwest Nigeria (Afolayan, 2015). The major above-ground biomass that directly influences soil nutrient status in cocoa plantations is uptake of nutrient for bean and podhusk development. Nutrient mobility is another cause of variation in the aboveground biomass. For instance, nitrogen, phosphorus and potassium concentrate more on young foliage than the old leaf. Phosphorus according to Marschner (1995) is mobile in the plant and, when a deficiency occurs, it moved from the older leaves to the younger leaves at the top of the plant. The concentration of N, P and K decreased during or just prior to senescence, because these elements are translocated away from the drying leaves (Small, 1972; Sreekala, 2001). In tropical region where cocoa is predominantly grown, application of chemical fertilizer has not been widely practiced among the farmers except disease resistant chemical seasonally applied. Previous studies have been focused majorly on the soil without NJAFE VOL. 12 No. 4,

2 combine both (soil-plant) properties. Most of the problems in agricultural practice persist due to the solely concentration of the study on soil alone. In order to put the lasting solution to the militating problem of soil-plant nutrient degradation in mature cocoa farms in tropical agroecological, attention from mere descriptive methods of study to multivariate analysis of both plant and soil nutrient is highly required. MATERIALS AND METHODS Ondo State is located in the south-western Nigeria approximately between latitudes 5 45' and 7 52' N and longitudes 4 20' and 6 05' E. The State is bounded on the east by Edo and Delta States, on the west by Ogun and Osun States, on the north by Ekiti and Kogi States and to the south by the Bight of Benin and Atlantic Ocean. The State covers an estimated area of 15,820 km 2. Three communities out of the eighteen existing Local Government Areas (Alade; Idanre), (Ijegunma; Owo) and (Oniparaga; Odigbo) in Ondo State were chosen for this study based on their annual rate of cocoa production over the years. Plantations between the ages of were selected in each of the community. The climate of Ondo State is of the lowland tropical rain forest type, with distinct wet and dry seasons. The rainy season starts from April to October with double maxima rainfall (June/July) and slight dry season between November and March. In the southern part of the study area, rain falls throughout the year with mean annual rainfall of about 2000 mm and above, but the three months of November - January may be relatively dry. The study area is characterized with mean monthly temperature of about 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. The vegetation of Ondo State is classified under tropical high rainforest agro-ecological zone, an ideal belt for the production of tree crops. The soil of Ondo State soil is characterized by very deep and well-drained soil; loam sandy surface, sandy clay and clay loamy subsoil (Ajayi et al., 2009; Afolayan, 2015). The southern part of the State is characterized with sedimentary rock in the south and basement complex rock in the north (Daramola et al., 2009). Sampling and data collection under this study were subdivided into soil and plant sampling. Physico-chemical properties from both were used as primary data for further analysis. Selected physicochemical parameters were the basis for the growth and development of cocoa as well as determinant factors of soil fertility in cocoa ecosystem. From 25 m by 25 m quadrat selected in cocoa farm, twelve (12) soil samples were randomly collected from two different depths 0-15cm and 15-30cm considered as topsoil and subsoil, respectively. Sampling was limited to these zones due to the fact that the most feeding roots of cocoa are concentrated in that depth (Thong and Ng, 1978; Wood and Lass, 1985; De Oliveira and Valle, 1990). In each of the quadrat, twelve (12) cocoa plant variables (leaf, pod and litter) which have been identified as outputs in cocoa plantation were sampled in October, They were made up of fresh leaf, cocoa bean and pod husk. The fresh leaf samples were air-dried, whereas cocoa pod husk were pulverized before chemical analysis. Cocoa beans were fermented for five days and sun-dried also. In line with Aikpokpodion (2010), dried cocoa beans and pod husks were grounded while leaves were pulverized before subject to laboratory analysis for the; ph, nitrogen, phosphorus, calcium, potassium, magnesium and sodium and trace elements; zinc, copper, iron and manganese. Soil particles were air-dried, pulverized and sieved with 2.0 mm sieve mesh and analyzed. Soil ph was determined potentiometrically in 0.01M calcium chloride solid to liquid solution ratio of 1:2 according to Peech (1965). Organic carbon was determined using the chromic acid digestion method (Walkley and Black, 1934). Extracts of soil sample leached with 1NB ammonium acetate were used to determine the concentrations of exchangeable cations, thereafter Ca, K and Mg were determined by atomic absorption and Na was determined by flame photometry. Total nitrogen was determined by the Kjedahl method and available phosphorus was determined by the Bray method (Jackson, 1970). Extractable micronutrients (Zn, Cu, Ni, and Mn) were measured after extraction with 0.02M EDTA using atomic absorption spectrophotometer (Isaac and Korber, 1971). Laboratory results on soil-plant chemical properties were subjected to descriptive and inferential statistics. Results were arranged in tabular form according to the mean value of each variable. Analysis of Variance was used to examine the differences within the soil-plant variables while student t-test was used to compare the mean value between soil and plant chemical properties. Also, contribution of the each of the plant variables to the soil nutrient status was addressed through multiple regression analysis. RESULTS AND DISCUSSION Soil ph in this study ranges from and result shows that fresh leaf and litterfall had higher ph (6.38 and 6.78), respectively. Soil records high storage of Nitrogen while litter has the lowest (0.23%), although soil critical value is placed to be 0.09% (Egbe et al., 1989). Concentration of organic carbon seems to be higher in cocoa bean compared to other variables. Its concentration in the soil is less than critical value of 3.0%. This may be attributed to the extraction by the plant parts. Also, organic carbon usually concentrated in the living biomass. Potassium (K) was within the soil critical limit (0.03 cmokg -1 ) in Idanre and Odigbo but higher (0.4 cmokg -1 ) in Owo. This may be linked to the soil physical difference and mobility factor. Nitrogen, phosphorus and potassium are the most mobile nutrient in the soil (Brady and Weil, 1999). Its concentration was very high in cocoa podhusk followed by the fresh leaf. The increasing order of K concentration in the examined cocoa plant variables were NJAFE VOL. 12 No. 4,

3 podhusk > fresh leave > bean > leave > soil. Magnesium concentration remains 0.01cmo kg -1 across the three locations which is less than soil critical limit of 0.8cmo kg-1 for cocoa production whereas litterfall and fresh leaf account for the highest of its storage capability (litterfall) and (fresh leaf). Aikpokpodion (2010) affirmed that Mg in most of the cocoa producing area due to over-mining of the nutrient without replacement in southwest were depleted and has been the major consequence of low production. The same pattern applied to calcium, the most available cation in Southwest Nigeria soil. Availability of P in the soil is very low in Idanre and Odigbo below the critical limit of 10mg kg -1 and high in Owo (11.14 mg kg -1 ). Fresh leaf capability of P storage seemed to be high compared to other cocoa plant variable. The magnitude order of P concentration from Table 1 was fresh leaf > bean > litter > soil. Availability of micronutrients were higher in the soil than plant variable and this may be due to their immobility in the soil as well as deposit from the applied chemical in resistant against the pathogens. They were less than the critical values except Zn that falls between mgkg -1 above 1.0 mgkg -1. In cocoa agroforestry, associated plants stored 70%, cocoa 5%, litter 20%, root 7% and soil 15% of the carbon stock in cocoa ecosystem (Sonwa et al., 2009; Seidu, 2010). The aged cocoa farms stored more carbon than young farms and associated trees stored 2 times more than cocoa (Nathalie et al., 2012). Among the examined cocoa plant variables fresh leaf, bean and podhusk were considered as nutrient outputs and litterfall as input (Table 2). The impact of fresh leaf in terms of nutrient uptake from the soil is very negligible across the study areas. Multiple regression analysis showed with negative value (nutrient input) and positive value (output) for other variables across the three locations. Result shows that irrespective of the amount of the nutrient extracted from the soil, at least about 38% of it naturally returned litterfall. In some cases, the quantity may even exceed the amount uptake for the fresh leaf development condition which may be attributed to the impact of the litterfall from the shaded trees. According to Hartermink (2005), litterfall is subdivided into the litter from cocoa and shade trees and includes branches, twigs, leaves, fruits and flowers. Large amount of nutrient is required for leaf development in Owo (85%) and Odigbo (76%) compared to Idanre (40%). Also, Idanre showed the litterfall efficiency (44.4%) than Odigbo (26.2%) and Owo (7.3%). Low nutrient return in the latter farm may be linked to the slow decomposition of cocoa leaves. Sarah (1992) emphasized that those grown on nutrient poor soils produce recalcitrant litter that decomposes slowly, whereas those that occur on fertile soil produce easily degraded litter. It seems that organic materials, especially leaves emanating from kola decomposed faster than that emanating from cocoa because cocoa leaves are lignified making the leaves decompose very slowly (Ekanade, 1990). Podhusk contribution to the soil degradation reflected more in Owo (26.6%) than other locations with 2.7% and - 5.6% respectively. This implies the possibility of rapid soil nutrient deterioration through podhusk especially in Owo than other areas. Cocoa bean was the only variable that shows the highest contribution to the soil degradation across the study areas with p-values of 0.036, and 0.029, respectively. Table 2 shows the order of the nutrient variability in order of 1.21, 1.29, 1.58; corresponding with 0.64, 0.81, and 0.91 for Owo, Odigbo and Idanre. Idanre: Y = (Fresh Leaf) (Litterfall) (Bean) (Husk) Owo: R 2 = 0.64; S.E. = 1.58 Y = (Fresh Leaf) (Litterfall) (Bean) (Husk) R 2 =0.91; S.E. =1.21 Odigbo: Y = (Fresh Leaf) (Litterfall) (Bean) (Husk) R 2 = 0.81; S.E. =1.29 Comparative analysis of nutrients status in cocoa variety Due to nutrient uptake, soil properties varied from hybrid to indigenous cocoa plantations. Comparison from inferential statistics point of view, there were no statistical differences between the soil properties in indigenous and hybrid cocoa plantations across the study area. However, observed differences were not statistically significant. Table 4 shows the summary of the paired t-test for the examined parameters. Using Student s t-test statistics to compare the different between hybrid and indigenous cocoa soil properties shows that there were no significant differences between their mean values. With table value of in relation to the degree of freedom (d.f) of 18, all calculated values were less than 0.05 level of significant. This indicates lack of significant difference between the compared means. Differences between both soil properties in Idanre show negative (-) t- value (-0.970) with corresponding calculated value of Result shows the t-value of , and 0.262) corresponds with and significance level respectively. Variation in the nutrient return via litter between both varieties may be as a result of the nutrient uptake difference and quality of the litter. There may be variation in the quality of lignin because cocoa leaf is said to be lignified. According to Ekanade (1990), Ogunkunle and Awotoye (2011), it seems that organic materials, especially leaves emanating from kola decompose faster than those emanating from cocoa because cocoa leaves are lignified making cocoa leaves decomposed very slowly. The rate of decomposition may also vary between hybrid and indigenous cocoa varieties as well. NJAFE VOL. 12 No. 4,

4 Table 1: Soil-plant chemical properties in cocoa farms in ondo state Idanre (Alade) Owo (Ijeguma) Odigbo (Oniparaga) Properties S FL L B H S FL L B H S FL L B H SCV ph N (%) OC (%) K (cmo kg -1 ) Ca (cmo kg -1 ) Mg (cmo kg -1 ) Na (cmo kg -1 ) NA P (mg kg -1 ) Zn (mg kg -1 ) >1.0 Mn (mg kg -1 ) Fe (mg kg -1 ) >4.5 Cu (mg kg -1 ) Source: Author s Data Analysis (2015). Note: S-Soil, FL-Fresh Leaf, L-Litterfall, B-Bean, H-Husk, SCV-Soil Critical Value, mg/kg -1 - milligram per kilogram, cmo kg -1 - centimole per kilogram NJAFE VOL. 12 No. 4,

5 Table 2: Soil Nutrient Determinants in Aged Cocoa Farms Idanre Unstandardized Coefficients B Std. Error Beta Standardized Coefficients 1 (Constant) Fresh Leaf Litterfall Bean Husk Owo 1 (Constant) Odigbo Fresh Leaf Litterfall Bean Husk (Constant) Fresh Leaf Litterfall Bean Husk Table 3: Analysis of Variance on Soil-Plant Chemical Properties in Cocoa Farms Model Sum of Squares df Mean Square F Sig. 1 Regression a Owo Residual Total Regression a Odigbo Residual Total Regression a Residual Total Table 4: Student T-Test on Soil Properties in the Study Area Paired Differences T df Sig. (2-tailed) 95% Confidence Std. Std. Error Interval of the Std. Std. Error Indigenous-Hybrid Mean Deviation Mean Difference Mean Deviation Mean Lower Upper Lower Upper Lower Upper Lower Upper Idanre Owo Odigbo CONCLUSION AND RECOMMENDATIONS Findings revealed that nutrient concentration in soil and plant varied with respect to the season and cocoa species. The development of fresh leaf in old cocoa farm required high nutrient especially in Owo and Odigbo compared to Idanre due to many years of nutrient mining without replacement through fertilizer. Also, litterfall efficiency was high in Idanre and Odigbo as a result of the impact of spatially integrated shaded trees. The study observed the possibility of rapid soil nutrient degradation in Owo than other areas due to the nutrient stocked in cocoa bean and podhusk. To increase nutrient efficiency in old cocoa farm through litterfall, spatial integration of shaded T Sig. NJAFE VOL. 12 No. 4,

6 trees, seasonal spreading of accumulated podhusk are required since average cocoa farmers in southwest Nigeria are not use to chemical fertilizer application. REFERENCES Afolayan, O. S 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. Aikpokpodion, P. E Nutrient Dynamics in Cocoa Soils, Leaf and Beans in Ondo State, Nigeria. Journal of Agricultural Science. 1(1):1-9. Ajayi, I. R., Afolabi, M. O., Ogunbodede, E. F. and Sunday, A. G Modeling 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 Comparative Analysis of Soil Nutrient Degradation in Hybrid and Indigenous Cocoa Plantations in Southwest Nigeria. Zaria Geographer. 21(1): Bremner, J. M 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 Diagnostic Survey Report of Ondo State Agricultural Production. Institute of Food Security, Environmental Resources and Agricultural Research. p2. de Oliveira, L. J. and Valle, R. R 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 Soil and Nutrition of Cocoa, Coffee, Kola, Cashew and Tea. Progress in Tree Crop Research in Nigeria. 2: Ekanade, O An Evaluation of Soil Productivity in under Interplanted Cocoa and Kola Environmental System in Southwestern Nigeria. International Journal of Environmental Studies. 35: Hartemink, A. E Nutrient Stocks, Nutrient Cycling and Soil Changes in Cocoa Ecosystems: A Review. Advance in Agronomy. 6: Isaac, A. R. and Korber, J. D Atomic Absorption and Flame Photometry; Techniques and Issues in soil, Plant and Water Analysis. In: I. M. Saish (Ed.) Instrumental Methods for Analysis of Soil and Plant Issues. Soil Sciences Society of America Publication Inc., Madison. Marschner, H Mineral Nutrition in High Plants. (2 nd Edition) Academic Press, San Diego, p McKenzie, R. H Micronutrient Requirement of Crops. Alberta Agriculture and Rural Development. (Accessed from on 20 th November, 2013) Nathalie, S. E. N., Denis, J. S. Benard, A. N. and Gochowski, J Tree Management in Cocoa Agroforestry of Southwest Cameroon: Implication for Livelihoods and Carbon Stocks. International Institute of Tropical Agriculture, Sustainable Tree Crops Program (Ghana). Ogunkunle, A. O and Awotoye, O. O Soil Fertility under Different Tree Cropping System in a Southwestern Zone of Nigeria. Notulae Scientia Biologicae. 3(2): Omotoso, T. I Amount of Nutrient removed from the Soil in Harvest Amelonado and F3 Amazon Cocoa during a Year. Turrialba, 235: Peech, M Hydrogen ion Acididty. In: C. A. Black (Ed.), Methods of Soil Analysis, 2. Robert, L. S Ecology and Field Biology. Fifth Edition. Harper Collins College Publishers, U.S.A. Sani, Y. and Jibril, E A Comparative Study of Nutrient Cycling on Soils Under Daniella Oliveri and Chromolaena Odorata in the Federal Capital Territory, Abuja, Nigeria. American Journal of Scientific Research. 10: Sarah, E. H Effect of Plant Species on Nutrient Cycling. Tree. 7(10): Seidu, M. K Mitigating Climate Change: What Role can the Cocoa Farmers in West Africa Play? 18 th Commonwealth Forestry Conference held in Ghana on 29 th June Sonwa, D. J., Weise, S. F., Nkongmenech, B. A., Tchatat, M. and Janssens, M. J. J Carbon Stock in Smallholder Chocolate Forest in Southern Cameroon and Potential Role in Climate Change Mitigation. Earth and Environmental Science. 6: 1-2. Sreekala, N. V. Mercy. G., John, P. S. and Vikraman, R Seasonal Variation in Elemental Composition of Cocoa Litter under Shade and Open Conditions. Journal of Tropical Agriculture, 39: Thong, K. C. and Ng, W. L Growth and Nutrient Composition of Mono-crop Cocoa Plants on Inland Malaysia Soil. In: Proceeding International Conference on Cocoa and Coconuts, Kuala Lumpur p Walkey, A. and Black, C. A An Examination of Degtagereft Method for Determining Soil Organic Matter and a Proposed Modification of Chronic Acid Titration Method. Soil Service. 37: Wood, G. A. R. and Lass, R. A Cocoa. 4 th Edition. Longman Scientific and Technical, Essex. NJAFE VOL. 12 No. 4,