Studies on the Growth of Rice Plants Cultivated in Different Seasons. : II. Changes of water- and soil temperature and oxidation potentials in paddy fields, and root development of rice plants.

Abstract

We investigated the changes of water-and soil temperature, redoxy potentials in paddy fields, as well as the changes of roots of rice plants, in relevance among them, in order to know the agronomical capability of different season cultivation of rice plants. It was found that in the early season cultivation water- and soil temperature were lower during the early course of growth, of course being influenced by natural temp. and also did not go up to higher degree even in hot days as compared with later season cultivation, being influenced by thick growth of Plants (Fig. 1, 2). In the shift of such soil temperature, Eh value of paddy field naturally was kept rather higher in early cultivation, and also its descending was slower (Fig. 3, 4). Accordingly the time of the occurence of rotted roots was so delayed that the total amount of such roots did not surpass, even at the time of harvest, half the amount of the rotted roots in usual-and late season culivation (Fig. 5). Healthy roots were many and better in morphological characters in early season cultivation than in other season cultivations as shown in Fig. 5. It may be duly supposed that the reason why early season cultivation can escape from so-called "autumn decline" lies on the fact of occuring of less rotted root.