Analysis of Yield-Determining Process and Its Application to Yield-Prediction and Culture Improvement of Lowland Rice : CIX. Effects of nitrogen top-dressing at full heading stage on lodging resistance, root activity, yield and kernel quality

Abstract

As stated in previous papers, the nitrogen top-dressing at full heading stage maintained high photosynthetic activity of leaves after heading and contributed to the increase in percentage of ripened grains, in the weight of 1000 grains and in yield. At the same time, it was known that protein content in brown rice fed by nitrogen top-dressing at full heading stage was raised by 20-30 % in comparison with that of control. The authors tried to make it clear that whether nitrogen top-dressing at full heading stage would have another effects besides the effects mentioned above. For instance, the question, does the top-dressing at full heading stage increase the root activity and the lodging resistance. or improve the qualities of rice grains?, was set in this experiment. To achieve this purpose, a different amount of nitrogen was individually applied at full heading stage in the form of ammonium sulphate, and the following results were obtained: 1. By nitrogen top-dressing at full heading stage, the percentage of ripened grains, the yield and the amount of dry matter accumulated after heading were increased as the dose rate of nitrogen was raised in the range of 3-9 g/m2. 2. By the same treatment, an activity of α-NA oxidation and O2 consumption by root was increased, and the rice plants were maintained freshly untill maturity. Consequently, the breaking strength at culm base and the lodging resistance became larger than those of control. 3. As to the quality of rice kernels, the following results were obtained by the same top-dressing ; a) the nitrogen content in brown rice was increased by 11-25 %, b) the number of kernels thicker than 2.0 mm was increased, and c) the percentage of perfect kernel was raised up, and the percentages of white belly (and core) rice and of milky white rice kernels was lowered, respectively, especially, characters described in this item were conspicuous in the plot where nitrogen was restricted during the period from 70 to 90 in leaf number index. 4. Effecfs of nitrogen top-dressing at full heading stage on nitrogen content in brown rice was more amplified in the case of upland conditions after heading and calcium basal dressing.