On the Regional Differences in the Agro-climatic Index on Quantity of Ripening of Rice Plant in Japan

Abstract

This report deals with the regional variation of the agro-climatic index on quantity of ripening under normal climate in Japan.
(1) Geographical distributions of the index varied with the heading date. At the early heading dates, that is, in the first half of August, the index in the north-eastern part of Japan was larger than those in the south-western part. Particularly, the index in the Japan Sea coast of north-eastern part of Japan was larger than those in the Pacific Ocean coast. The index in north-eastern part gradually decreased with the delay of the heading date. However, the index in the south-western part increased.
(2) The indices calculated for the period from August to September 20 were found to be relatively large in the Ishikari Plains of Hokkaido, in the Japan Sea coast of Tohoku district and in the western part of Kyushu (Fig. 3). On the contrary, the smaller values were obtained in the Kanto Plain.
The heading date to assure the maximam value of the index was found to be in the first part of August in Hokkaido and nerthern Tohoku. With movement from northen districts to southern districts nthey became late and September 10 in western Kyushu and southern Shikoku.
(3) Average air temperatures in the ripening period (from the heading date to the following 40 days) showing the maximum value of the index were about 21-22°C, everywhere. Therefore, the maximum index value at each place was mainly affected by the sunshine duration in the ripening period.
It can be concluded that important limiting factors in increasing the value of the index are low temperature in Hokkaido and Tohoku, high temperature in western Kyushu and insufficient sunshine in Kanto plain, respectively.