Effect of Water Depth, Amount of Irrigation Water, and Irrigation Timing on Water Temperature in Paddy Field during Continuous Irrigation with Cool Running-water

Abstract

Continuous irrigation with running water (CIRW) experiments were conducted in an experimental paddy field under different amount of irrigation water, water depth, and irrigation timing condition, and the effects of these irrigation conditions on water temperature in paddy field were studied. The effect of cooling by inflow of irrigation water exhibited positive and negative relationships with amount of irrigation water and water depth, respectively. CIRW during nighttime was more effective than that of daytime, under the same conditions of irrigation amount and weir height. On the other hand, changes in water temperature at the area that did not receive cool irrigation water became slower with increase in water depth that increased heat capacity of paddy water. Thus, higher (lower) water depth kept water temperature cooler in daytime (nighttime).