Differences in carbon and nitrogen retention and bacterial diversity in sandy soil in response to application methods of charred organic materials

Abstract The use of charred organic materials (biochar) as soil amendment can alter soil nutrient, microbial abundance, and their diversities. These alterations can be influenced by the biochar source, application method and amount, but the details are still unknown. Thus, this study aimed to compare two methods of biochar application (surface or mixed) on carbon (C) and nitrogen (N) losses with their related effect on microbial community under C-depleted sandy soil. Chicken manure (CM), rice husk (RH) and rice straw (RS), pyrolyzed at 350 °C to produce biochar, were tested in a pot trial. The biochar was applied singly, and in combined forms (CM + RH and CM + RS) under dent corn, as mixed (incorporated) or surface application, at different rates of 0, 15, and 30 g kg−1 soil (equivalent to 0, 7.5 and 15.0 Mg ha−1). The soil respiration (SR), leaching loss of organic-C and inorganic-N (as nitrate-N), microbial biomass C at top 10 cm soils, bacterial relative abundance and community structure were measured. The application methods' effect on SR was unclear but the surface application reduced the C leaching loss and increased nitrate-N loss compared to the mixed application, in general. The microbial biomass C was found to be significantly higher (P