Water-saving Irrigation Scheduling to Rice (Oryza sativa)in Indo-Gangetic Plains of India

摘要

Rice crop being less water efficient consumes about half of the total freshwater used for irrigation in Asia. Decreasing water resources and increasing costs of itsuse have necessitated the efforts for increasing water use efficiency of rice. Waterlosses in rice can be reduced by lowering seepage + percolation losses through reducedhydrostatic pressure. This can be achieved by keeping soil saturated or throughalternate wetting and drying. Implementing saturated conditions requires good watercontrol at the field level and frequent irrigations which is practically not possible. In caseof alternate wetting and drying, the interval between two irrigations is a combinedfunction of climatic conditions as well as type of soil. There is thus a challenge indeveloping water-efficient rice production system to reduce water inputs whilemaintaining yields at the same high level as that under flooded conditions. The presentstudy is a step towards meeting this challenge and aims at scheduling irrigation to riceon the basis of soil matric potential. Experiments were conducted in rice for four yearson a sandy loam soil with differential irrigation scheduling. The treatments comprised of5 levels of soil matric suction viz. 80 ± 20, 120 ± 20, 160 ± 20, 200 ± 20 and 240 ± 20 cmbesides irrigation as per recommended practice of irrigation 2 days after completeinfiltration of ponded water. The rice yield was not affected when irrigated at soil matricsuction values of up to 160 ± 20 cm during all the years of study compared to that withrecommended practice. Increasing soil matric suction to 200 ± 20 cm reduced the riceyield by 0-5.8% during 2000-2003. The amount of irrigation water used decreased withincrease in soil matric suction. At soil matric suction of 160 ± 20 cm it decreased by 30-35% during 2000-2003. The irrigation water used at 160 ± 20 cm was a direct function ofnumber of rainy days. It was maximum (131 cm) during 2002 due to highest amount ofevaporation (678 cm) and minimum number of rainy days (18). On the other hand, it wasminimum (70 cm) during 2003 and it may be due to lowest amount of evaporation (410.1mm) and highest number of rainy days (35). The total amount of rain could not explainthese variations in amount of irrigation water used. The gap between two irrigationsrecorded during 2002 was 3.5, 4.5, 5.5, 6.5 and 8 days at 80, 120, 160, 200 and 240 ±20 cm soil matric suction values, respectively compared to 3 days in case ofrecommended practice. The percolation losses of water in rice fields were found to be afunction of ponding water depth and was affected by pre-puddling tillage and puddlingintensity on a similar soil.