Comparison of Water Absorption by Paddy-and Upland-Rice under Upland Field Conditions

Abstract

With a view to determining the quantity and frequency of irrigation adequate for paddy rice when it is grown on upland fields, water use by the plant and its root distribution were investigated in comparison with those of upland rice, in 1957-'58. The results obtained were as follows: 1) Water requirement of paddy rice was 280-290 and rather less than that of upland rice (290-300). 2) Though the ratio of the amount of water transpired after heading time to its total amount transpired during the whole life, in both cases of paddy rice and upland rice, was higher under the paddy field condition than under the upland field condition, and the earlier the heading the higher was this ratio, this ratio was higher in paddy rice than in upland rice in every case. 3) The number of roots distributed in the 0-10cm. soil layer were more and in deeper layers it was fewer in paddy rice than in upland rice, with the result that the water content of the soil of the field where paddy rice was grown was lower in the shallow layer and higher in the deep layer than that of the field planted with upland rice. The weight of roots of the paddy rice were less than those of the upland rice both in the shallow and deep layers. These results led us to the conclusion that it should be necessary to irrigate paddy rice on upland fields with somewhat shorter intervals and with larger quantities of water, especially for the period after heading time as compared with upland rice