水稲早期栽培における用水量について

抄録

The early season cultivation of rice has widely spread with an extreme speed in the the southwestern part of Japan owing to its many advantages. Accordingly, it has come to be indispensable to obtain the adequate knowledge of the water requirements for the early season cultivation in order to establish rational irrigation plans. The authors, therefore, have pursued these studies through experiments since 1958.
The maximum water requirement for the customary cultivation of rice appeared in the middle of the growing season, and the water requirement rapidly decreased in the ripening stage. The maximum water requirement for the early season cultivation, on the other hand, were seen in the latter half of the growing period, and the water requirement in ripening stage was still great. The above results have lead to the following conclusion : when the early season cultivation is introduced into the regions of the customary cultivation, the maximum water requirement is to appear on contignous days in the two methods, though transplantation is made about one month and a half earlier in the early season cultivation. Accordingly, it is impossible to decrease the value of the maximum water requirement by the combination of the both cultivations.
In such regions where the water quantity for “shirokaki” ((puddling preparation of paddy field for transplantation)) is a dominant factor for the irrigation planning, it is possible to decrease the water quantity for shirokaki by the combination of the both cultivations. Therefore, it is advantageous for irrigation planning to introduce the early season cultivation.
The maximum intensity of transpiration in the customary cultivation of rice was seen before the heading stage. On the other hand, it was seen after the heading stage in the early season cultivation. The remarkable phenomenon suggests different physiological characters between paddy rice in the customary cultivation and in the early season cultivation, and attracts the attention of the authors.