Biochar and Inorganic NPK Fertilizer or Compost Application Improves Soil Quality and Cabbage Yield

Soil fertility decline and loss of organic matter are widespread challenges to crop production in sub-Saharan Africa (SSA). Combined biochar and compost application has potential to increase crop yield due to direct nutrient addition and liming effect, particularly in acidic soils, which enhances nutrient use efficiency. The study examined the effect of biochar (B) and / or compost (C) application on soil physicochemical properties characteristics, cabbage yield, and N and P uptake and use efficiencies, compared to sole application of either input or inorganic NPK fertilizer in a highly weathered Haplic Acrisol under humid tropical climatic conditions. Biochar or compost (10 ha-1) were incorporated solely or in combination (BC) in a 12-week field experiment. The results showed that addition of biochar and/ or compost increased soil pH, Total Organic Carbon (TOC) and available P and lowered soil exchangeable acidity. Furthermore, combined application of biochar and/ compost significantly increased cabbage head N and P uptake, resulting in greater biomass and cabbage head dry weights of 9 to 18% and 10-29%, respectively. Agronomic efficiency of N was significantly higher in C and NPK than B and CB, physiological efficiency of N was higher in B and CB than NPK and C. The inorganic NPK treatment showed greater apparent N recoveries of 48%, followed by the sole compost treatment which showed ARE of 39.6% for N. The sole biochar and the combined biochar and compost treatments showed less than 25% Apparent Nutrient Recovery Efficiency (ARE) for N, suggesting that N could have been retained in the soils amended with biochar solely or together with compost. We conclude that combined biochar and compost application is a sustainable soil fertility management approach for cabbage production in low nutrient and highly weathered soils in SSA.