Cocoa Soils Research Articles

Cocoa pod husk-derived organic soil amendments differentially affect soil fertility, nutrient leaching, and greenhouse gas emissions in cocoa soils

The depletion of soil nutrients and decline in yields on cocoa farms in west Africa over time force farmers to abandon their farms and look for new fertile land, thereby contributing to deforestation. Cocoa pod husks (CPH) are a major farm waste representing considerable export of nutrients from cocoa soils, particularly P and K. Here, the impacts of soil amendment with raw CPH residues, CPH compost, CPH biochar, or a CPH compost-biochar mixture on soil fertility, greenhouse gas (GHG) emissions, and nutrient losses via leaching were assessed in two laboratory experiments using two major soil types used for cocoa cultivation in Ghana (an acidic Ferralsol and an alkaline Nitisol). In Experiment 1, soil nutrient availability and CO2 and N2O emissions were quantified, whereas simulation and quantification of nutrient leaching were conducted in Experiment 2. Soil pH increased from 4.8 to 8.6 by 1.4- and 1.1-folds on average in amended Ferralsols and Nitisols, respectively. Soil electrical conductivity increased in soils amended with CPH compost and/or biochar. Addition of raw CPH caused remarkable microbial immobilisation of N and reduced N availability and leaching, whereas CPH compost and/or biochar addition increased soil nitrate availability but reduced soil ammonium availability. Leaching of Ca in Nitisols was reduced when CPH biochar was included in the soil amendment. While soil K availability increased in all amended soils, most notably when CPH biochar was included, soil P and Ca availabilities were greatest where CPH compost was included. Soil total GHG emission (CO2 plus N2O) increased in all amended Ferralsols and the Nitisols amended with CPH compost or raw CPH, with the latter remarkably increasing soil CO2 emission by up to 14.8-folds. Compared to sole CPH compost amendment, CPH compost-biochar mixture amendment reduced soil total GHG emission and N and P leaching. These findings show that composted and/or pyrolysed CPH can be judiciously used to enhance soil fertility in cocoa farms, particularly in acidic soils. Pyrolysed CPH is especially beneficial for reducing soil nutrient leaching and GHG emissions and thus for increasing the sustainability of cocoa production in Ghana and west Africa.

Heavy metal status in cocoa (Theobroma cacao L.) soils and beans: the case of Abuakwa North Municipality of Eastern Region, Ghana.

In recent times, public concerns over the potential accumulation of heavy metals in agricultural soils and crops due to the excessive use of agrochemicals are increasing. This study was conducted in the Abuakwa North Municipality of Eastern Region, Ghana, to assess the status of heavy metals in cocoa soils and beans. Cocoa farms aged between 10 and 20years and have received agrochemicals for at least 5years were selected, and their adjacent forests were used as controls. Soil samples and cocoa pods were collected randomly and processed for laboratory analysis. The study discovered that across the sampling sites, heavy metal concentrations in soil were below permissible limits. However, contamination factor and geo-accumulation index results revealed that Tontro cocoa farms were considerably contaminated and moderately polluted respectively with Cu, probably due to long-term fungicide application. The concentrations of Fe (39.3-47.1mgkg-1) and Zn (54.8-70.0mgkg-1) in the cocoa beans across the communities were below the FAO/WHO's safe limit of 99.4mgkg-1 and 73.0mgkg-1 respectively. Lead (0.03-0.06mgkg-1) and Cd (0.12-0.20mgkg-1) concentrations were below the EU's maximum allowable level and Codex Alimentarius Commission's limit of 1.0mgkg-1 respectively. However, bean Cu content in the Tontro farm (51.5mgkg-1) was slightly above the EU's recommended maximum limit of 50.0mgkg-1, possibly due to the continuous application of copper-based fungicides. The study showed that, overall, agrochemicals used for cocoa farming in Abuakwa North Municipality of Ghana did not cause serious harm to the soils and beans, since the mean metal concentrations were not alarming and guarantee public health safety.

Geochemical dynamics of Cu(II) in contrasting cocoa soils: Kinetics and isotherm modeling

Understanding copper (Cu) dynamics in cocoa soils can help predict the fate, mobility, and toxicity, which is crucial for sustaining soil functionality, as well as the quality and health safety of cocoa products. Herein, the study investigated sorption-desorption characteristics of Cu(II) in six cocoa soils of varying weathering by kinetics, isothermal, and pH effect experiments in a batch system. Equilibrium sorption increased in the order of Fluvisol < Lixisol < Luvisol < Acrisol = Ferralsol = Nitisol. Kinetics data fitted well to pseudo-second-order and Elovich models. Cu(II) sorption was dominated by outer-sphere and inner-sphere complexations at low and high pH, respectively. The sorption data fitted well with Freundlich and Langmuir's models. Sorption maximum increased in the order of Nitisol (0.91 mg g−1) < Ferralsol (1.21 mg g−1) < Acrisol (1.29 mg g−1) < Lixisol (1.61 mg g−1) < Luvisol (1.68 mg g−1) < Fluvisol (2.01 mg g−1). The binding energy values obtained showed the highest interaction between Cu(II) and soil matrix in Fluvisol and the least in Ferralsol and Nitisol. The desorption studies consistent with the hysteresis index indicated high sorption irreversibility and less Cu(II) mobilization in Fluvisol, Lixisol, Luvisol, and Acrisol vis-à-vis Nitisol and Ferralsol. Nitisol and Ferralsol may promote the possible toxicity of Cu(II) to the soil ecosystem. The study contributes to the sensitivity of Cu(II) mobility and toxicity to the degree of soil weathering; thus, management of heavy metals in cocoa soils should be dependent on soil type.

Presence of cadmium in cocoa (Theobroma cacao, L.) soils in the province of Esmeraldas-Ecuador

The province of Esmeraldas, where the research was carried out, is recognized for the quality of its fine aroma cocoa (Theobroma cacao, L.), which is highly sought after internationally, but the regulation for cadmium by the European Union has restricted its commercialization, for Therefore, with the objective of evaluating the presence of cadmium in the soil, leaves and almonds, to establish its mobility and absorption by the plant, 51 farms from the Eloy Alfaro, Muisne and Atacames cantons were sampled that have cocoa crops of more than 5 years of age, applying a zig zag sampling, the lowest average values of cadmium in the soil were found in Colón Eloy (0.064 ppm.Kg-1), while the highest were obtained in the soils of Muisne and Atacames (0.147 and 0.145 ppm.Kg-1 respectively); in the leaves, the data were 6.96 and 11.50 ppm.Kg-1 for these locations, respectively. In cocoa beans, both in Colón Eloy, Muisne and Atacames, they were high (1.09; 1.99 and 2.08 ppm.Kg-1, respectively) with respect to the maximum limits of Cd, established by the European Union (0.10 to 0.80 μg .kg-1). It is concluded that the analyzed samples yielded values greater than 0.1 ppm.Kg-1 considered contaminants, due to the fact that Cd, due to its mobility, is easily absorbed by cocoa plants, which is reflected in its content in the leaves and fruits, for Therefore, remedial measures must be applied to help producers recover their commercialization in the world.

Survival of mushrooms and termites upon pesticide exposure in the cocoa agro-ecosystem

Pesticides have become integral parts of cocoa cultivation for the management of insect pests and fungal pathogens which cause significant damage to the crop. However, continuous pesticides usage in the cocoa agro-ecosystem is of concern due to perceived adverse effects on non-target organisms. In this study, mushrooms and associated termites were used to elucidate the possible effect of insecticides and fungicides on non-target organisms in the cocoa agro-ecosystem. Vegetative phase of Pleurotus sajor-caju (Oyster mushroom), Volvariella volvacea (Paddy straw mushroom), Termitomyces globulus and Termitomyces robustus (Termite mushrooms) were subjected to concentrations of commercially formulated fungicides (metalaxyl 12 % + copper (I) oxide 60 % and cupric hydroxide 77 %) and insecticides (imidacloprid 20 % and bifenthrin 2.7 %) to observe their growth rates on Potato Dextrose Agar (PDA) medium. Worker termites, Macrotermes bellicosus, were also exposed to the pesticides in Petri dishes for 24 h to observe their mortality. The manufacturer’s recommended concentration of 245 ppm for bifenthrin completely inhibited mycelial growth of all the mushrooms and caused 100% mortality of termites. At 0.0245 ppm, the insecticide caused 60% mortality of termites, but it had no inhibitory effect on the mushrooms. Except P. sajor-caju, mycelial growth of all the other mushrooms were completely inhibited by metalaxyl + copper (I) oxide at the manufacturer’s recommended concentration of 2400 ppm. However, mycelial growth rate of the mushrooms at 0.24 ppm of the fungicide was similar to the control plates. This suggests that mushrooms could survive in the cocoa agro-ecosystem amidst pesticides at lower concentrations in cocoa soils.

Concentration Of Micronutrient (Fe, Cu, Mn) In Cocoa Plantation Land In Transmigration Area, East Luwu Regency

Micronutrients such as Fe, Cu and Mn function to help maintain land productivity, improve soil fertility that has been lost, and increase crop production. Micronutrients are also required for metabolic activity and growth in cocoa plants. Therefore, it is necessary to pay attention to the micronutrient content in the soil where cocoa plants grow. The purpose of this study was to determine the content of micronutrients (Fe, Cu, and Mn) in regional plantation soils. The analysis method uses Inductively Coupled Plasma. The results showed that the micronutrient content in cocoa soil with 5 locations was Iron (Fe), Copper (Cu), and Manganese (Mn) with an average of 1056.050 mg/100g; 3.816 mg/100g; and 53.350 mg/100g.

Talaromyces santanderensis: A New Cadmium-Tolerant Fungus from Cacao Soils in Colombia.

Inorganic pollutants in Colombian cocoa (Theobroma cacao L.) agrosystems cause problems in the production, quality, and exportation of this raw material worldwide. There has been an increased interest in bioprospecting studies of different fungal species focused on the biosorption of heavy metals. Furthermore, fungi constitute a valuable, profitable, ecological, and efficient natural soil resource that could be considered in the integrated management of cadmium mitigation. This study reports a new species of Talaromyces isolated from a cocoa soil sample collected in San Vicente de Chucurí, Colombia. T. santanderensis is featured by Lemon Yellow (R. Pl. IV) mycelium on CYA, mono-to-biverticillade conidiophores, and acerose phialides. T. santanderensis is distinguished from related species by its growth rate on CYAS and powdery textures on MEA, YES and OA, high acid production on CREA and smaller conidia. It is differentiated from T. lentulus by its growth rate on CYA medium at 37 °C without exudate production, its cream (R. PI. XVI) margin on MEA, and dense sporulation on YES and CYA. Phylogenetic analysis was performed using a polyphasic approach, including different phylogenetic analyses of combined and individual ITS, CaM, BenA, and RPB2 gene sequences that indicate that it is new to science and is named Talaromyces santanderensis sp. nov. This new species belongs to the Talaromyces section and is closely related to T. lentulus, T. soli, T. tumuli, and T. pratensis (inside the T. pinophilus species complex) in the inferred phylogeny. Mycelia growth of the fungal strains was subjected to a range of 0–400 mg/kg Cd and incorporated into malt extract agar (MEA) in triplicates. Fungal radial growth was recorded every three days over a 13-day incubation period and In vitro cadmium tolerance tests showed a high tolerance index (0.81) when the mycelium was exposed to 300 mg/kg of Cd. Results suggest that T. santanderensis showed tolerance to Cd concentrations that exceed the permissible limits for contaminated soils, and it is promising for its use in bioremediation strategies to eliminate Cd from highly contaminated agricultural soils.

Tolerance and Cadmium (Cd) Immobilization by Native Bacteria Isolated in Cocoa Soils with Increased Metal Content

Twelve cadmium native bacteria previously isolated in soils of cocoa farms located in the western Colombian Andes (Santander), and tolerant to 2500 µM CdCl2 (120 mg Cd/L), were chosen in order to test their tolerance and Cd immobilization using liquid culture medium (Nutritive broth) at different concentrations of heavy metals. Furthermore, in the greenhouse experiments, the strains Exiguobacterium sp. (11-4A), Klebsiella variicola sp. (18-4B), and Enterobacter sp. (29-4B) were applied in combined treatments using CCN51 cacao genotype seeds grown in soil with different concentrations of Cd. All bacterial strains’ cell morphologies were deformed in TEM pictures, which also identified six strain interactions with biosorption and four strain capacities for bioaccumulation; FT-IR suggested that the amide, carbonyl, hydroxyl, ethyl, and phosphate groups on the bacteria biomass were the main Cd binding sites. In the pot experiments, the concentration of Cd was distributed throughout the cacao plant, but certain degrees of immobilization of Cd can occur in soil to prevent an increase in this level in roots with the presence of Klebsiella sp.

Discovering the Diversity of Arbuscular Mycorrhizal Fungi Associated with Two Cultivation Practices of Theobroma cacao

In recent years, new data on the diversity of genera and species in the phylum Glomeromycota continue to be added and rearranged. Arbuscular mycorrhizal fungi are key to plant nutrition and agriculture. Studies report different short- and long-term cultivation practices that influence the abundance and diversity of Glomeromycota. To the best of our knowledge, there are no known studies of the fungal communities in the fine aroma cocoa cultivars. In this context, our work aims to discover the diversity of arbuscular mycorrhizae associated with two cocoa cultivation practices (conservative and semi-conservative) through the isolation of spores using microscopy and metabarcoding of the internal transcribed spacer region (ITS). Morphological analysis showed that the density of Glomeromycota spores exhibited significant differences between production systems. Although the metabarcoding analysis showed that diversity indices showed a higher increase in the roots than in the cocoa soil, independently of the cultivation practice. An abundance of 348 and 114 taxa were observed, corresponding to the conservative and semi-conservative practices, respectively. Seven genera were observed for the first time in cocoa crop agroforestry systems, including P. scintillans, R. diaphanus, R. fasciculatus, R. custos, D. disticha, M. perpusilla, and D. bernensis.

Distribusi C-Organik pada Berbagai Jenis Tanah dan Kedalamannya di Kabupaten Gayo Lues

Abstract .Soil is the largest carbon reservoir in terrestrial ecosystems, half of the carbon enters the soil through plant residues and other soil organisms that decompose and accumulate in the soil. Each type of soil has a different amount of carbon with the depth of the soil. This study aims to determine the distribution of C-organic in the soil of Podsolic Brown and Podsolic Merah Yellow with its depth. This study used a survey method accompanied by field observations accompanied by soil sampling based on land map units (SPL). The data from the research were interpreted and then analyzed descriptively to describe the distribution of C-organic in the two types of soil studied. The results showed that Podsolic Cocoa soil had a total C-organic content of 7, 03% (high) and Red Yellow Podsolik had a total organic C of 3.99% (medium). Distribution of C-organic namely C-total, C-Free, C-Bound Clay, and C-Bound sesquioxides in each type and depth of soil has a different amount of carbon. Brown Podsolic and Red Yellow Podsolic soils have the same pattern, namely the higher the soil depth, the lower the organic C content.Distribution of Organik Carbon in Variety Types of the Depth in Gayo Lues RegencyAbstract. Soil is the largest carbon reservoir in terrestrial ecosystems, half of the carbon enters the soil through plant residues and other soil organisms that decompose and accumulate in the soil. Each type of soil has a different amount of carbon with the depth of the soil. This study aims to determine the distribution of C-organic in the soil of Podsolic Brown and Podsolic Merah Yellow with its depth. This study used a survey method accompanied by field observations accompanied by soil sampling based on land map units (SPL). The data from the research were interpreted and then analyzed descriptively to describe the distribution of C-organic in the two types of soil studied. The results showed that the Brown Podsolic soil had a total C-organic content of 7.03% (high) than the Red Yellow Podsolic had a total C-organic content of 3.99% (medium). Distribution of C-organic, namely C-total, C-Free, C-Bound Clay, and C-bound sesquioxides in Brown Podsolic and Red Yellow Podsolic soils had the same pattern, namely the higher the soil depth, the lower the C-organic content.

Effects of landuse change and topography on the quantity and distribution of soil organic carbon stocks on Acrisol catenas in tropical small-scale shade cocoa systems of the Ashanti region of Ghana

Landuse conversion is the highest contributor to atmospheric CO2 in the tropics. While forest conversion to agriculture results in the depletion of soil organic carbon (SOC), cocoa agroforestry may improve SOC stocks. The aim of our study was to explore the effects of topography and landuse change from forest to cocoa agroforestry on the quantity, quality, and distribution of SOC stocks. A total of 324 soil samples from the upper 0–145 cm were collected from catenas with 3 replicates along 3 hillslope positions: upper hillslope/summit position, middle hillslope/backslope position and lower hillslopes/foot- or toeslope positions. SOC stocks were highest in the upper hillslope positions at the 0–30 and 0–60 cm depths and varied from 42.85 ± 10.91 to 44.04 ± 13.70 Mg C ha−1 (0–30 cm depth) and 57.66 ± 18.80 to 60.32 ± 16.36 Mg C ha−1 (0–60 cm depth) for land use types. Hillslope position (upper, middle or lower) significantly affected humic substances with the topsoil having more humified organic materials in the upper compared to other hillslope positions. Forest conversion to shaded-cocoa had a strong impact on the quality of humic substances. Cocoa agroforestry systems had significantly lower E4:E6 ratios with more labile carbon at the lower slope positions compared to similar positions in forest systems. The most labile and readily available organic molecules (fulvic acids) are under forest systems whereas higher proportion of stabilized less soluble organic molecules (lower E4:E6 ratio) are found in cocoa soils in the form of humic acids. Slope position impacted E4:E6 ratios with lower degree of humification of organic materials in lower hillslope positions across the two landuses. A positive correlation was observed between humic substances and clay content. Our study contributes to the understanding of the influence of topography on SOC quantity and quality in forest and cocoa systems in Ghana.

Assessing the condition and capability of soils in cocoa districts of Ghana using geovisualization

Improving agricultural soil conditions is essential for attaining global soil security against land degradation. This requires the use of complex geospatial farm soil information, the absence of which hinders sustainable cocoa (Theobroma cacao L.) soil management in West Africa. This study seeks to create geospatial visibility (awareness) on the conditions and capabilities of cocoa soils. Specifically, to examine the geospatial distribution of soil organic carbon (OC), clay, pH, iron (Fe) and aluminium (Al) in the entire cocoa-growing Districts of Ghana. A visual analysis of geographically referenced secondary data from farm soil survey conducted by the National Cocoa Rehabilitation Programme (NCRP) of Ghana Cocoa Board (COCOBOD) was made. The data were collected based on stratified random sampling of soils at 20 cm depth in 739 newly established cocoa farms, covering 60 Districts. R-GIS enabled descriptive analysis that showed District level mean and standard deviation of these soil properties in colour-graduated thematic maps. Generally, Cocoa District soils were low with 0.42 g kg−1 OC, 5.3 pH, 0.09 cmolc kg−1 Fe with Al in excess of 7.48 cmolc kg−1. Soil clay capability was 22.2%. Combined with a dearth of awareness, policy and economic incentives to improve these conditions, imply cocoa soil security is very low as well. The geovisual maps provide spatially explicit soil information for managing and monitoring cocoa soil security, specifically, Al, OC and pH at the Districts. Farmers, agricultural extension workers, soil scientists, agronomists, policymakers like COCOBOD and development practitioners may use these findings as a guide for restoring cocoa soils.

Evaluation of the Capacity of Agroforestry of Cocoa Trees in Atmospheric Carbon Dioxide Reduction

&#x0D; &#x0D; &#x0D; The emission of greenhouse gases into the earth’s atmosphere has been credited as the major cause of climate change which is being experienced all over the world. Climate change mitigation is one of the strategies that have been suggested as a way of stabilising the concentration of greenhouse gases in the atmosphere. This study assessed the capacity of agroforestry of cocoa trees in reducing atmospheric carbon dioxide. The carbon content in the cocoa plant variables made up of bean, litter, leaf and podhusk were determined in the laboratory through standard procedure. The laboratory results were subjected to descriptive and inferential statistical techniques. The study showed the magnitude order of carbon storage in cocoa agroforestry as cocoa bean (2.86 kg) &gt; pod husk (2.73 kg) &gt; cocoa litter (2.65kg) &gt; cocoa leaves (2.62 kg) &gt; soil (1.14 kg)..The ability of cocoa and forest soils to retain nitrogen, leaf and litterfall to stock more carbon proved that cocoa agroforestry has a higher potential of mitigating climate change in the tropical region. The study recommended the adoption of agroforestry systems which are capable of sequestering carbon as a means of addressing the challenge of climate change.&#x0D; &#x0D; &#x0D;

Medium-term effect of fertilizer, compost, and dolomite on cocoa soil and productivity in Sulawesi, Indonesia

AbstractIn Indonesia, management practices that reduce soil fertility could be limiting cocoa (Theobroma cacao L.) production. To address this, we investigated the effects of fertilizers and organic amendments comprising different combinations of NPK + urea, dolomite, and manure-based compost on soil properties and cocoa productivity. We extended an existing field experiment in South Sulawesi, Indonesia, to assess these treatments’ effects on cocoa trees from the age of 2.9 years to 7.4 years. The treatments were first applied 5 months after planting and subsequently twice a year. Soil analyses were performed before planting, after 3 years, and finally after 7 years. Productivity was assessed yearly between the age of 3.5 and 7.4 years. The highest yields were obtained from the plots receiving compost, although the yield benefits diminished over time. Inorganic fertilizer alone doubled the yield compared to the control, while the yields with compost and compost + fertilizer were three times that of the control. With dolomite alone, the yield cumulated over 4 years was 41% higher than the control. The positive effect of compost on cocoa yields can potentially be attributed to (1) physical changes increasing soil water availability, (2) the chemical improvement of nutrient availability, and (3) biologically, by promoting the activity of beneficial organisms. The application of dolomite increased soil pH, Ca, and Mg contents. Soil organic carbon greatly declined in the composted treatments, even though 10 kg of compost was applied per tree per year, probably because of the low C:N ratio of the compost. Future studies should assess different fertilizer formulations and combinations with organic inputs and explore the mechanisms by which compost promotes cocoa productivity.

Geospatial distribution of soil organic carbon and soil pH within the cocoa agroecological zones of Ghana

Geospatial distribution of soil organic carbon (SOC) and soil pH is an important component of soil fertility management in sustainable cocoa (Theobroma cacao L.) production. Spatial precision of cocoa soil fertility management in Ghana is rare due to paucity of spatially precise knowledge of farm soil properties. This study sought to provide spatially explicit knowledge of the underlying trends of SOC and pH in and across cocoa agroecological zones, covering 61 cocoa districts in Ghana. Soil samples collected at 20 cm depth from 739 newly established cocoa farms were analyzed using classical and geospatial statistical methods. We described the spatial pattern (clustering) of SOC and pH and predicted their spatial continuity from observed and unobserved locations. Results generally revealed unsuitably low SOC (0.39 ± 0.009 g/100 g) and strong acidity (5.35 ± 0.027). Univariately, SOC varied more continuously (58%) over a longer distance (1.424 km) than pH, which varied moderately around 55.7% over a shorter distance (0.598 km). Covariates improved the co-regionalized structure and homogeneity of the predictions. Thus, the spatial dependencies of SOC and pH were moderate but the risk of imprecision was higher for SOC than pH. This knowledge is crucial in our understanding of the geo-physicochemical phenomena controlling the spatial distribution of SOC and pH in the cocoa farms and districts across the agroecological zones. The findings underscored dwindling SOC and pH in line with historic boom-bust cycle of cocoa production hot and cold spots transitions. The findings are also indicative of the adverse implications of relying on current blanket fertilizer recommendations. Therefore, a change from the current agronomic practice of fertilizer use to one that recognizes the SOC and pH needs of specific areas, farms and cluster of districts is recommended.

Tolerance and Cadmium (Cd) Immobilization by Native Bacteria Isolated in Cocoa Soils with Presence of Metal

Tolerance and Cadmium (Cd) Immobilization by Native Bacteria Isolated in Cocoa Soils with Presence of Metal

Growth and flowering of young cocoa plants is promoted by organic and nitrate-based fertiliser amendments

SummaryCocoa (Theobroma cacao) farmers in Sulawesi, Indonesia typically use subsidised, ammonium-based rice fertilisers that in combination with poor agricultural practices have resulted in soil acidification, loss of organic matter, aluminium toxicity and lower soil fertility. As a result, these soils are only marginally appropriate for replanting cocoa to boost production. A field experiment was performed to test alternative soil amendments for successful replanting of cocoa on these deficient soils. In a trial with a randomised block design, 6-month old seedlings, top-grafted with the local MCC02 clone, were planted under light Gliricidia sepium shade and after 3 months treated quarterly with two options of mineral fertilisers: either a customised fertiliser, consisting of Nitrabor (a combination of calcium nitrate and boron), dolomite, rock phosphate and KCl or a NPK/urea mix used by farmers, each supplied with or without ‘micronutrient’ rock salt, organic fertiliser and beneficial microorganisms or their culture medium, a mixture of chitin and amino acids (a total of 20 treatments). Over a 4-year period, the marginal mean rates of stem diameter increment and flowering score were higher in customised fertiliser than NPK/urea treatments. The average growth rate was highest in the first year and was increased by supplying organic fertiliser. A significant correlation (r = 0.22, p &lt; 0.05) occurred between growth and available P, but concentrations of available P were higher in the NPK/urea plots, which also had lower mean growth rates. Combined supply of organic fertiliser and microbes increased available P, as well as growth rates, in both the customised and NPK/urea treatments. In contrast, NPK/urea-treated plots without these amendments demonstrated very low growth rates. The customised formulation was more effective with or without added organic fertiliser or inoculated microbes. Micronutrient supply stimulated flowering. Growth rates in trees supplied with NPK/urea were also promoted by micronutrients. Leaf flush production occurred in regular cycles and was unaffected by the nutrient amendments. After 3 years, the customised and organic fertiliser application increased soil pH and exchangeable Ca and Mg concentrations, although they remained below recommended levels for cocoa production. These treatments had little impact on soil C content (about 1.3%) which was also deficient. Exchangeable Al and total Zn concentrations were higher in soils amended with NPK/urea. The results of the trial provide evidence that utilisation of organic fertiliser in combination with customised nitrate-based formulations improves cocoa establishment, growth and soil properties and should be recommended as a replacement for the NPK/urea fertilisers traditionally used by farmers.

Factors Determining the Characteristics of Cocoa Soil in Sulawesi

Sulawesi exhibits unique land characteristics as a result of complex geological and geomorphological processes. The information related to what extent of theseprocesses affect regional soil characteristics is still limited. An investigation was performed on cocoa farms from three major cocoa producers, i.e. South Sulawesi, Central Sulawesi, and Southeast Sulawesi. A research was done to point out the key variables contributing to cocoa soil characteristics. Soil survey was performed based on available local information to collect top soil composite samples, i.e. 0–30 cm depth, in the circle of cocoa stand within 50–75 cm radius. A routine soil analysis was done to evaluate soil texture, organic carbon (C), total nitrogen, K, Ca, Mg, soil pH (H2O), and some micronutrients, i.e. Fe, Cu, and Zn. To simplify the complexity, the multivariate data was submitted into principal component analysis (PCA). Additional mapping of soil variable gradient through inverse distance weighting (IDW) interpolation was included in the analysis to improve our interpretations. Data show that the variability for almost all investigated variables is high with coefficient of variation (CV) of up to about 118% for Fe. While low variability with CV about 10% was observed for soil pH (H2O). The PCA demonstrates that the first five principal components (PCs) account for 56.89% of variance in the original variables. Two factors to be considered to explain the variation in the PCs was soil texture and parent material. Further analyses exhibit an association of sand, silt, and clay fractions to Southeast, Central, and South Sulawesi. Mineral compositions, such as K, Ca, Mg, Fe, and Zn, exhibit an important contribution to the parent material factor as they define the variability in the PCs. Additionally, the analysis of gradient maps may indicate the two physical environmental conditions, i.e. landform and geological setting, contribute to the specific characteristics of cocoa soil.

Assessing the relationship between soil quality parameters of Nigerian alfisols and cocoa yield

Soil quality is widely regarded as an important factor in sustainable agriculture and is often assessed by evaluating the pertinent physical, chemical and biological properties of soils. The aims of this study were to (i) establish a minimum data set (MDS) of soil quality parameters capable of monitoring changes in soil condition and ecosystem functioning in smallholder cocoa production systems on tropical alfisols in southwest Nigeria; and (ii) examine the relationship between selected MDS of soil quality parameters and cocoa yield along a chronosequence of 3-, 7-, 15-, 22-, 30-, 40-, 60- and 80-year-old farm plots. To achieve these aims, five plots were identified for each plantation age group and bulk soil samples were collected at a depth of 0–20 cm. The samples were analysed for a total data set (TDS) of twenty-three separate soil quality parameters. Principal component analysis (PCA) was employed to reduce the dimensionality of the TDS to five principal components. The PCA results showed that five principal components with eigenvalues > 1 explained more than 78% of the variability in the soil properties. Within PC1–PC5, eleven (11) soil quality parameters with high loadings were identified and selected as the MDS. A stepwise multiple regression analysis of cocoa yield and MDS revealed that soil organic matter and cation exchange capacity are the key parameters influencing cocoa yield. To maintain the yield as well as long-term sustainability of smallholder cocoa farming systems, inorganic fertilizer application is needed. Considering the poor transportation system in rural areas and prohibitive costs associated with inorganic fertilizer application in cocoa plantations, it is suggested that organic materials such as cocoa pod husk should be used to improve soil health. Another proposed approach for improving the N content of cocoa soils is to inter-crop nitrogen-fixing legumes.

Development of a composite soil degradation assessment index for cocoa agroecosystems in southwestern Nigeria

Abstract. Cocoa agroecosystems are a major land-use type in the tropical rainforest belt of West Africa, reportedly associated with several ecological changes, including soil degradation. This study aims to develop a composite soil degradation assessment index (CSDI) for determining the degradation level of cocoa soils under smallholder agroecosystems of southwestern Nigeria. Plots where natural forests have been converted to cocoa agroecosystems of ages 1–10, 11–40, and 41–80 years, respectively representing young cocoa plantations (YCPs), mature cocoa plantations (MCPs), and senescent cocoa plantations (SCPs), were identified to represent the biological cycle of the cocoa tree. Soil samples were collected at a depth of 0 to 20 cm in each plot and analysed in terms of their physical, chemical, and biological properties. Factor analysis of soil data revealed four major interacting soil degradation processes: decline in soil nutrients, loss of soil organic matter, increase in soil acidity, and the breakdown of soil textural characteristics over time. These processes were represented by eight soil properties (extractable zinc, silt, soil organic matter (SOM), cation exchange capacity (CEC), available phosphorus, total porosity, pH, and clay content). These soil properties were subjected to forward stepwise discriminant analysis (STEPDA), and the result showed that four soil properties (extractable zinc, cation exchange capacity, SOM, and clay content) are the most useful in separating the studied soils into YCP, MCP, and SCP. In this way, we have sufficiently eliminated redundancy in the final selection of soil degradation indicators. Based on these four soil parameters, a CSDI was developed and used to classify selected cocoa soils into three different classes of degradation. The results revealed that 65 % of the selected cocoa farms are moderately degraded, while 18 % have a high degradation status. The numerical value of the CSDI as an objective index of soil degradation under cocoa agroecosystems was statistically validated. The results of this study reveal that soil management should promote activities that help to increase organic matter and reduce Zn deficiency over the cocoa growth cycle. Finally, the newly developed CSDI can provide an early warning of soil degradation processes and help farmers and extension officers to implement rehabilitation practices on degraded cocoa soils.