Short-term biochar application induced variations in C and N mineralization in a compost-amended tropical soil.

To mitigate food shortage due to global warming, developing sustainable management practices to stabilize soil organic matter (SOM) and sequester more carbon (C) in the cultivated soils is necessary, particularly in subtropical and tropical areas. A short-term (56 days) incubation experiment was conducted to evaluate the influences of rice husk biochar (RHB) and manure compost (MC) application on C mineralization and nitrogen (N) immobilization in a sandy loam soil. The RHB was separately incorporated into the soil at application rates of 2 and 4% (w/w) either with or without 1% (w/w) compost. Our results displayed that macroaggregates (≥2 mm) were obviously increased by 11% in soil amended with RHB + MC at the end of incubation. In addition, the experimental results presented that the C mineralization of the soil rapidly increased during the first week of incubation. However, the co-application of compost with biochar (RHB + MC) revealed that CO2 emission was significantly decreased by 13-20% compared to the soil with only MC. In addition, the mineralized N in the soil was lower in RHB + MC-amended soil simultaneously than only MC-amended soil, indicating that biochar addition induced N immobilization. The physical protection of compost by its occlusion into aggregates or adsorption on surface of RHB as proved by the micromorphological observation was the main reason for lower C and N mineralization in soil amended with RHB + MC. Overall results revealed that RHB + MC treatment can decrease the decomposition of compost and sequester more C in the tropical agricultural soils.