2022 Volume 93 Issue 4 Pages 176-184
To achieve both stable yield and good quality in “Hatsushimo Gifu SL,” the main rice cultivar in the flat land of Gifu Prefecture, appropriate application rates of nitrogen fertilizer were estimated considering the amount of nitrogen mineralization from the topsoils of paddy fields.
The amount of nitrogen uptake at rice maturity (N-uptake) was correlated with grain yield and the number of proteins in brown rice. Based on these relationships, the ideal N-uptake of “Hatsushimo Gifu SL” was determined as 100-kg ha−1．
A strong correlation was observed between the N-uptake and the amount of nitrogen supplied by nitrogen fertilizer (F-N) and that of nitrogen mineralized from paddy soils (S-N). The latter value was calculated from nitrogen mineralization when moist soil from paddy fields was incubated under submerged conditions at 30°C for 10 weeks (M10w). These results indicate that N-uptake was well predicted from N supply by F-N and S-N when M10w was used. However, the correlations were much stronger when the datasets were categorized based on the field use, i.e., continuously irrigated paddy rice fields or fields with a crop rotation of paddy rice and upland crops.
A formula for predicting N-uptake was developed using F-N, M10w, and the amount of nitrogen supplied from sources other than F-N and S-N. Using this formula, the ideal N-uptake and varying values of M10w, the appropriate nitrogen application rates could be predicted for the “Hatsushimo Gifu SL” cultivar.
