Reduction of milky white rice grain generation and qualitative improvement of rice grain of ""Koshihikari"" by using basal application of controlled-release coated urea

We studied the effect of the basal application of controlled-release coated urea (LPSS100) to rice variety gKoshihikarih in terms of the quality of rice grain. Qualitative improvement of rice grain is a very important theme for increasing the competitiveness among different rice growing areas. In Fukui prefecture, development of countermeasures to reduce the generation of milky white grain is one of the most important issues. We used LPSS100 for a fertilizer applicator-rice transplanter after compounding with quick-acting fertilizer, and examined growth, grain yields, ear characteristics and quality of rice grain. LPSS was applied in the soil when rice plant was transplanted, and we measured the soil temperature and examined the nitrogen release from LPSS100. The result obtained are summarized as follows: 1. Nitrogen release from LPSS100 was not observed in the early growth stage of rice plant. But nitrogen began to release at the panicle formation stage, when the integrated temperature reached about 1330 deg C/day. Its release pattern looked like a sigmoidal curve. At the panicle formation stage, 10% of applied N was released, and this ratio was stable in the every investigated year. 2. At an early growth stage, growth of rice plant was the same between the basal application plots and the control plots. But at the panicle formation stage, the leaf color was deeper in the basal application plots than in the control. And the absorption of nitrogen was the same as, or superior to, that in the control. After the topdressing at the panicle formation stage, however, the leaf color and the absorption of nitrogen in the control plots became superior to those in the basal application plots, and this situation continued until harvest. 3. Grain yields in the basal application plots were almost equal to those in the control. But the quality of the grain improved comparatively. These results were mainly due to reduction of the number of spikelets and also likely had much to do with the nitrogen release pattern of LPSS100 in the ripening stage. 4. In addition, we examined ear characteristics. For the primary and the secondary rachis branch, the ripening ratio was higher in the basal application plots than in the control. And in the basal application plots, the milky white grain ratio and the protein content in bulled rice of the primary and the secondary rachis branch were less than those in the control plots. So the quality of grain improved in the basal application techniques considerably. 5. Although basal application techniques of controlled-release urea do not always increase yields, we believe that they deserve more attention as low-input sustainable techniques for qualitative improvement of rice grain.