Can combined compost and biochar application improve the quality of a highly weathered coastal savanna soil?

Abstract

Soil fertility decline represents a major constraint to crop productivity in sub-Saharan Africa. Many studies have shown that addition of biochar or compost can effectively improve soil quality. Biochar produced from crop residues are often N-poor but rich in stable C while poultry manure composts, which is often rich in nutrients including N decomposes rapidly under high rainfall and temperature conditions. Combined biochar and compost application can compensate for the shortcomings of each other such that their interactive effect is likely to improve soil quality. A 30-days incubation experiment was carried out on a Haplic acrisol amended with corn cob biochar, rice husk biochar, coconut husk biochar, poultry manure compost and composted rice husk or corn cob biochar to examine the effect of compost and biochar, applied singly, in combination or as co-compost on basal soil respiration, and soil quality indicators such as soil pH; soil microbial carbon; cation exchange capacity; total organic carbon, total nitrogen and available nitrogen concentration. The results showed that addition of the different amendments increased soil pH compared with the untreated control with the combined corn cob and rice biochar and compost treatments recording the highest pH values. Basal respiration following sole compost, composted biochar and combined biochar and compost application were significantly greater than the sole biochar and the control treatments. TOC increased by 37% in the sole compost treatment to 117.3% in the combined corn cob biochar and compost treatment, respectively. MBC increased by 132.2% in the combined rice husk biochar and compost treatment and by 247% in the sole compost treatment compared to the control. The study has demonstrated the potential of compost, biochar and especially composted biochar to enhance soil quality, C stabilization and reduce soil C loss through basal respiration.