Estimation of N Mineralization Potential and N Mineralization Rate of Organic Amendments as Affected by C:N Ratio and Temperature in Paddy Soil

Abstract

Understanding N mineralization dynamics in soil is essential for efficient nutrient management. An anaerobic incubation experiment was conducted to examine N mineralization potential and N mineralization rate of the organic amendments with different C:N ratio in paddy soil. Inorganic N in the soil sample was measured periodically under three temperature conditions (20°C, 25°C, 30°C) for 90 days. N mineralization was accelerated as the temperature rises by approximately 10% °C -1 in average. Negative correlation (R 2 = 0.707) was observed between soil inorganic N and C:N ratio, while total organic carbon extract (R 2 = 0.947) and microbial biomass C (R 2 = 0.824) in the soil were positively related to C:N ratio. Single exponential model was applied for quantitative evaluation of N mineralization process. Model parameter for N mineralization rate, k, increased in proportion to temperature. N mineralization potential, N p , was very different depending on C:N ratio of organic input. N p value decreased as C:N ratio increased, ranged from 74.3 mg kg -1 in a low C:N ratio (12.0 in hairy vetch) to 15.1 mg kg -1 in a high C:N ratio (78.2 in rice straw). This result indicated that the amount of inorganic N available for crop uptake can be predicted by temperature and C:N ratio of organic amendment. Consequently, it is suggested that the amount of organic fertilizer application in paddy soil would be determined based on temperature observations and C:N ratio, which represent the decomposition characteristics of organic amendments.