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 NO3 ˉ 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 NO3 ˉ 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 NO3 ˉ by 14%, whereas cow manure increased NH4+ by 128% and NO3 ˉ 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.