Seasonal Variation of Net Assimilation Rate (NAR) of rice plants

Abstract

For the purpose of obtaining some data serving as the basic ones for analyzing the relationship of rice growing seasons or areas to rice yields, authors tested the seasonal changes in NAR of rice plants, i. e., the seasonal changes in NAR in response to those in solar radiation and air temperature. For this test, Fujiminori Variety's young seedlings (at the fourth-leaf fully developed stage) grown in soil cultures were used as samples. The test results might be summarized as follows: 1. It was noted that NAR at the daily mean air temperature of 15°to 21°C changed favorably in proportion to the increases both in solar radiation and air temperature, but at the temperature of 21°to 30°C, NAR changed in response only to the increase in solar radiation, irrespective of air temperature. 2. Based upon the test results showing the above-mentioned seasonal changes in NAR as well as upon the daily mean solar radiation and air temperature at Zentsuji (in Shikoku), authors could observe the probable seasonal changes in NAR as described below in the months from late April to late October. 3. It was estimated that NAR took a rapid upward trend in the month from late April to late May, but in June it showed a rather retarding trend. After the opening of July, however, NAR continued to take the upward trend again, thus reaching the peak in late July and then it dropped with rapidity.