Predicting the appropriate application rates of nitrogen fertilizer for rice cultivar “Koshihikari” in the Hida region based on the amount of nitrogen mineralization in moist paddy soils incubated under submerged conditions

Abstract

The appropriate application rates of nitrogen (N) fertilizer were estimated based on the amount of N mineralization in the topsoil of paddy fields to achieve both good quality and taste and stable yield in “Koshihikari”, the main rice cultivar in the Hida region of Gifu prefecture (Hida Koshihikari). The amount of N uptake (N uptake) at rice maturity was correlated with grain yield and protein levels in brown rice. These relationships indicated that the ideal N uptake of Hida Koshihikari was 80-85 kg ha⁻¹. Furthermore, N uptake at the panicle formation stage was significantly correlated with the amount of N supplied by the basal N fertilizer (B-N) in addition to the amount of N mineralized from paddy soils (S-N). The latter value was calculated from N mineralization when moist topsoil taken from paddy fields were incubated under submerged conditions at 30°C for 10 weeks (M10 w). These results demonstrate an accurate prediction of the N uptake at the panicle formation stage from the N supply by B-N and S-N when M10 w was used. B-N, M10 w, and N supplied from sources other than B-N and S-N were used to develop a linear equation for predicting N uptake at the panicle formation stage. This formula, along with the N uptake value at the panicle formation stage and varying values of M10 w, was used to calculate the appropriate N application rates for basal fertilizer in Hida Koshihikari. However, N uptake after the panicle formation stage was strongly affected by the amount of N supplied by top-dressed N fertilizer. Therefore, these relationships could be used to estimate the appropriate N application rates for top-dressing from the N uptake after the panicle formation stage.