Responses of grain chalky traits to nitrogen application levels for different growth-period Japonica cultivars

The appearance quality is one of the important aspects of rice quality. Nitrogen is the indispensable nutrient to rice production although over application of N could cause so many environment problems. The effect of nitrogen application rates on appearance quality is varied in different rice cultivars, especially in different genotypes. Therefore it is necessary to identify the responses of grain chalky traits to nitrogen application levels for different growth-period Japonica cultivars. In this research, a field experiment with four nitrogen levels (zero, low, medium and high) was carried out. About 56 Japonica rice cultivars which are representative in the region of Yangtze River were adopted to investigate the differences of the rice types under the four nitrogen levels. The chalkiness degree was clustered and selected in term of their different responses to the nitrogen application levels. The main results are as follows: 1) In the range of 0-300 kg/ha nitrogen fertilization, the effects of nitrogen application rates on rice chalkiness rate are genotype-dependent, with the increasing chalky-grain rate in high level for medium growth-period Japonica cultivars, while the dropping one for late growth-period Japonica cultivars. With the level of nitrogen increased, the chalkiness degree of Japonica rice cultivars is increased. 2) All 56 rice cultivars can be classified into three types (insensitive, intermediate and sensitive) in term of their different responses of grain chalkiness degree to the nitrogen application levels. And two rice groups among them are also recommended. One group is the cultivars with low and stable chalkiness degree under all nitrogen levels; the other group is the cultivars which are sensitive to nitrogen application levels, and good appearance quality can be obtained through the proper reducing nitrogen application.