Nitrogen mineralization from rice straw and cow manure with various moisture conditions in organic paddy fields

Nitrogen is an essential element, which can come from mineralization of organic N in plant residues. The measurement of nitrogen mineralization is important for estimating nitrogen availability and determining fertilizer requirements. This study aims to evaluate N mineralization of straw and cow manure in organic paddy fields at different water conditions through laboratory incubation. Types of paddy field management (organic, semi-organic, and conventional), organic matter (straw and cow manure), and moisture conditions (aerobic and anaerobic) were used in these research. The NH4+ and NO3ˉ concentration, soil pH, and water content were measured eight times over 56 days of incubation. Microbial biomass was measured at the end of the incubation. The data were analyzed using three-way ANOVA followed by the DMR and Pearson correlation test. Results showed that the application of cow manure on organic paddy fields in anaerobic conditions increased NH4+ up to 18.56 mg kg-1 and increased NO3ˉ in aerobic conditions up to 7.71 mg kg-1 from the initial concentration. Organic paddy fields with cow manure input under anaerobic conditions have the highest N mineralization potential. The N mineralization rate of straw and cow manure in organic paddy fields under anaerobic conditions was not significantly different. For 8-week incubation, adding straw in organic paddy fields increased NH4+ by 109% and NO3ˉ by 14%, whereas cow manure increased NH4+ by 128% and NO3ˉ by 18%. Application of plant residue or manure is an effective strategy to enhance soil microbial biomass and soil N availability and has the potential to reduce the dependence upon chemical N fertilization.