Fundamental Studies of Irrigation of Upland Fields. : VI. Some water absorption characteristics of paddy rice plants cultivated in upland fields in early season.

Abstract

Recently the irrigation of upland fields has spread in our country. Some farmers who are engaged in the irrigation wish to introduce paddy rice plants into upland fields just as they have cultivated upland rice plants in the same fields. The characteristics of water absorption of paddy rice plants when cultivated in paddy fields are known to some extent, but those are hardly known when they are cultivated in upland fields. The authors studied the water absorption characteristics of the paddy rice in upland fields with automatic recorders already reported in the previous paper. The results are as follows : 1) The water absorption by root of paddy rice plants in upland fields in early season increased proportionally to their top growth, reached a maximum in anthesis, and afterwards decreased with ripening. This tendency was almost the same as that of upland rice reported by one of the authors (TAMAI, 1950) (Fig. 1). 2) Fig. 2 shows variations of the amount of water absorption of paddy rice plants (variety YACHIKOGANE), which were planted on 17 th of April and 27 th of May, during the whole growing season. The maximum period of water absorption varied according to the date of planting, but the period always coincided with the flowering period. 3) The paddy rices planted in the early season are harvested at the time of high temperature. Fig. 2 shows that the root of the plant in the harvest time had about a half of the water absorption ability of the maximum period. 4) Fig. 3 shows the comparison of the daily variation of water absorption in both the flowering and the ripening periods of paddy rices planted in different dates. Fig. 3 was plotted from the records presented in Fig. 4 It is confirmed from Fig. 3 that the daily variation of water absorption is very remarkable in the flowering period but becomes small in the ripening period to some extent. Fig. 5 also shows the same tendency as Fig. 3 The daily variation of water absorption of these paddy rices harvested in a hot season is still remarkable in the ripening period (just before harvesting). While, the daily variation of the same variety. harvested in autumn (bottom in Fig. 3) nearly disappears in the ripening period. 3) and 4) show the fact that the root of paddy rice plants grown in the early season and harvested in summer has a high ability of water absorption as compared with that of the same plant harvested in autumn. These results arouse our attention to the control of watering of paddy rices in the ripening period when they are cultivated in upland fields. 5) Table 1 shows water requirement and its original figures which are obtained under upland irrigation conditions. The water requirement has figures amounting to 300. The figures in the right column represent the amount of water which is needed to produce 1 liter of unhulled rice. It is said from these figures that the amount of water needed by paddy rice plants cultivated in upland fields is about 700 times of the volume of rice to be produced. These values seem to be near to the values obtained under paddy field conditions, but this point must be ascertained in future.