Effect of the Amount of Irrigation Water on Growth and Grain Yield of Grain Sorghum

Abstract

This experiment was conducted to evaluate the effect of the amount of irrigation water on growth and grain yield of grain sorghum during drought stress period and to make efficient use of irrigation water under four treatments : 0, 1, 2 and 3 irrigations per week. Twenty millimeters of water was applied at each irrigation time. Irrigation water was applied from July 12 to Augllst 2, when grain sorghum was heading time through milk stage. Leaf water potentials measured by pressure chamber (Daiki Rika K.K.) were affected by the quantity of irrigation water and lowered by less amount of irrigation water. The recovery of leaf water potential by irrigation was 2 to 3 bars and the difference of leaf water potential between well irrigated treatment (3 irrigations per week) and others was enlarged when drought stress was accelerated. Two irrigation treatment never became lower than - 19 bars which is a critical point of grain sorghum when stomata close. Leaf diffusive resistance measured by porometer (Lambda Instruments Corp.) was high in no and one irrigation treatments. However, it was low in two and three irrigation treatments and no difference was recognized between them. Top growth of grain sorghum was slowered and stopped by drought stress and its recovery after drought was small. Stressed top growth was mainly due to slow development of grain head and decay of lower leaves. Grain yields decreased as the amount of irrigation water decreased, but no statistical difference was recognized between well irrigated and two irrigation treatments. Reduced grain yields were attributed to low 1, 000 grain weight. From the results of grain yield and difference between evapotranspirations and the amounts of irrigation water during drought stress period, drought damage will be reduced by irrigation of about 40 millimeters of water a week.