Analysis of Yield-Determining Process and Its Application to Yield-Prediction and Culture Improvement of Lowland Rice CXX. Effects of the nitrogen restriction on the grain yield judged from the growth amount, the leaf color and the percentage of stained length of leaf sheath

Abstract

In order to obtain some informations whether the nitrogen restriction treatment was adequately carried out or not, the leaf color grade in field conditions, the growth amounts such as the dry weight, the number of tillers and the length of lower internodes (especially the fifth internode from the uppermost one) were individually checked at the late stage of spikelets initiation (90 in leaf number index). The effects of above mentioned factors on the lodging, 'the percentage of ripened grains and the grain yield, as far as var. Manryo was concerned, were summarized as follows: 1. As to the combined effects of nitrogen content in leaf blades and the top weight of the plant on the grain yield, two optimal combinations of the former and the latter, i.e., (2.2∼2.6%)×(500-600 g/m2) and (2.6∼3.0%)×(400∼500 g/m2), brought the highest yield. However, in case of the nitrogen content and the top weight being larger or smaller than the optimal values indicated above, the grain yield decreased. 2. Even if the nitrogen content in leaf blades was substituted by the ratio of the leaf color grade to the percentage of stained length of leaf sheath, and the dry weight of the top was replaced with the number of tillers, the similar relations mentioned above were recognized. For instance, the combination of 0.05∼0.08 in the ratio of the leaf color grade to the percentage of stained length of leaf sheath and 500∼700 tillers per square meter brought forth the maximum grain yield. 3. When the nitrogen content in leaf blades or the dry weight of the top exceeded their optimum, the decrease of the grain yield was brought about by the decrease of the percentage of ripened grains. This decrease of percentage was caused mainly through lodging which was attributed to the length of the fifth internode. 4. Judging from the factors mentioned above, the following conditions seemed to be desirable for raising of the grain yield. That is, a) 0.05∼0.08 in the ratio of the leaf color grade to the percentage of stained length of leaf sheath (or 2.2∼2.6% in nitrogen content of leaf blades), b) 500∼700 tillers per square meter (or 500∼600 g/m2 in dry weight of the top) and c) less than 4cm in length of the fifth internode.