New estimation model for paddy soil temperature in early growth stage, and its application to estimate nitrogen mineralization of organic fertilizer

Paddy soil temperatures (Ts) are required to evaluate the mineralization patterns of organic fertilizers in rice paddies. We have developed an estimation method for Ts based on the heat balance model using Agro-Meteorological Grid Square Data (AMD) with a horizontal resolution of 1 km x 1 km. The paddy water temperature (Tw) (daily mean, assuming leaf area index LAI = 0) was first calculated from the AMD using the heat balance equation. Next, the daily mean Ts was evaluated using the empirical relationship between Ts and Tw. The value of Ts can be expressed as a linear function of a time series for Tw for up to 3 days prior. At five test sites in Niigata prefecture, Japan, the mean difference and root mean square errors between the estimated and measured Ts ranged from -0.54 degrees C to 0.77 degrees C (mean: 0.00 degrees C) and from 0.53 degrees C to 1.21 degrees C (mean: 0.86 degrees C), respectively. Overall, the results using the estimated Ts were found to agree with the observations for each field. Using the developed Ts estimation method and the nitrogen (N) mineralization parameters of organic fertilizers, we estimated the N mineralization patterns of four fertilizers at five test sites. The results show a good agreement with the measured values. This suggests that the proposed Ts estimation method in conjunction with the AMD can be utilized to estimate the N mineralization of organic fertilizers applied in paddy fields in Niigata prefecture.