Analysis of Yield-Determining Process and Its Application to Yield-Prediction and Culture Improvement of Lowland Rice : CXIII. Effects of the nitrogen top-dressing at the full heading stage on kernel qualities

Abstract

As reported in the previous papers, 8, 16) the nitrogen top-dressing at the full heading stage increases the carbon assimilation rate after heading, the resistance to lodging as a result of starch accumulation in the culm base, and consequently the percentage of ripened grains as well as the yield, and furthermore, it also increases the nitrogen content in kernels. Therefore, the authors tried some experiments to clarify the effects of the nitrogen top- dressing at the full heading stage on the taste quality of kernels (evaluated by sensory test), on the inspection grade of brown rice, and on the content of 45Ca and 32P in rice plants. Results are summarized as follows: 1) As the nitrogen content in kernels increases, the taste quality of kernels evaluated by the sensory test tends to decrease. However, it is quite noticeable that the taste quality of samples of kernels differs with different varieties and different cultural methods even in cases in which the nitrogen contents in the samples are almost equal with one another. Accordingly, selecting the variety to be used and improving methods, such as top-dressing, one will be able to increase the nitrogen content in kernels without decreasing the taste quality of kernels. 2) From the results of a factorial experiment which consists of calcium and phosphorus applied at the transplanting time as a basal dressing, the nitrogen top-dressing at the full heading stage and the transplanting time, it is clearly recognized that the nitrogen top-dressing at the full heading stage increases both the percentage of ripened grains and the inspection grade of brown rice, and that the inspection grade goes up with an increase in the percentage of ripened grains. 3) The number of grains per square meter being equal with one another, the percentage of ripened grains increases with an increase in the number of grains on primary rachis branches against total number of grains on panicles. 4) From a tracer experiment, it is revealed that the amount of 32P and that of 45Ca which are accumulated in brown rice increases 80% and more than two times, respectively, by the nitrogen top-dressing at the full heading stage. 5) It seems that the nitrogen top-dressing at the full heading stage affects the nitrogen content in brown rice through the nitrogen content in rice plants, especially through leaf blades at the heading stage.