Carbon and nutrient dynamics in biochar co-composts and their effects on C balances, soil properties and crop yields in Ghana

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Soils in Sub-Saharan Africa are naturally low in SOC and nutrients and are often further degraded by unsustainable land management practices, resulting in low crop yields. Maintaining or better, increasing soil organic carbon plays a crucial role in enhancing soil fertility for sustainable agricultural production. However, the availability of materials for increasing SOC levels is limited in Africa, and their use is often accompanied by rapid mineralization and high leaching losses. Composting organic household and market wastes is an emerging technology in some areas but high carbon and nitrogen losses during production and after field application reduce its efficiency. Based on other studies and some own preliminary results, the addition of biochar appears to be a promising option for increasing compost stability and thus its suitability for improving soil fertility. However, the underlying mechanisms for C and nutrient retention during co-composting and soil incorporation are still poorly understood. Therefore, the general objectives of the project are i) to investigate the effects of biochar co-composting on C and N dynamics during composting and ii) to study and document the mechanisms underlying the effect of composted biochar application on soil quality indicators, greenhouse gas emissions and crop yield in typical soils used for agricultural production in Ghana.The project will be conducted as a collaborative study with Dr. Kwame Frimpong from the University of Cape Coast (Ghana) involving compost production, greenhouse experiments and field trials in Ghana and laboratory experiments and comprehensive physical, chemical and biological compost and soil characterization in Bochum. Compost will be produced from a mixture of organic household wastes, rice straw and poultry manure, amended with different rates of two different biochars (from rice husks and corn cobs). During compost production and after its application to the three field sites in Ghana, the emissions of greenhouse gases (CO2, N2O, NH3 and CH4) will be monitored. The associated changes in biochar and biochar-compost properties will be analyzed in samples exposed in mesh bags in the compost and in the field. Source-differentiated C balances will be calculated from 13C data and C-stabilizing mechanisms will be determined from sequential extractions and from density and aggregate fractions. Together with the yield data from the greenhouse and field experiments, the results of this study will show if the production and application of biochar co-composts can enhance C sequestration, soil fertility and crop yield in these tropical soils.