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Li S.,State Key Laboratory of Eco Hydraulic Engineering in Shaanxi | Luo W.,Yangzhou University | Jia Z.,Yangzhou University | Tang S.,State Key Laboratory of Eco Hydraulic Engineering in Shaanxi | Wu D.,State Key Laboratory of Eco Hydraulic Engineering in Shaanxi
Shuili Xuebao/Journal of Hydraulic Engineering | Year: 2015

Properly raise water table with controlled drainage may increase shallow groundwater which can be used by crops, mitigating the water shortage in subhumid irrigated areas. However, salinity in groundwater over there is generally higher, and increasing use of shallow groundwater may speed up salt accumulation in the root zone and shorten the salt leaching cycle; this is not desired in these areas because the leaching water can hardly be ensured during the required period. Considering in the subhumid irrigation areas there are certain amount of rainfall that may produce leaching effect for salinity control, an analytical model was developed for calculating salt leaching cycle under controlled drainage. The model was tested subsequently through a case study in a subhumid irrigation area in which soil was reclaimed from salinization. With the daily water balance predicted by the field hydrology model-DRAINMOD, we calculated the salt accumulation in the root zone over a long term period (1951-2005) under controlled drainage and different supplemental irrigation depths. The results show that when groundwater depth is controlled at 1.2 m, rainfall has some effect on salt leaching even without irrigation; but soil salinity grows with time in the root zone. When the supplementary irrigation depth is greater than 150 mm, rainfall can effectively control the root zone salinity to reach a favorable salt balance in the case study area. Findings from this research indicate that in subhumid irrigation areas, considering the leaching effect of rainfall, proper water table management with controlled drainage can effectively control soil salinity for crop production and improve water use efficiency. ©, 2015, China Water Power Press. All right reserved. Source


Li S.,State Key Laboratory of Eco Hydraulic Engineering in Shaanxi | Luo W.,State Key Laboratory of Eco Hydraulic Engineering in Shaanxi | Jia Z.-H.,State Key Laboratory of Eco Hydraulic Engineering in Shaanxi | Pan Y.-X.,State Key Laboratory of Eco Hydraulic Engineering in Shaanxi | Wu D.,State Key Laboratory of Eco Hydraulic Engineering in Shaanxi
Shuili Xuebao/Journal of Hydraulic Engineering | Year: 2014

Water table management in irrigated areas may increase shallow groundwater use by crops. But the high salt content of groundwater results in faster buildup of salinity in crop root zone, which in turn affects leaching schedule of the irrigation districts. Based on general salt and water balance in crop fields in irrigated areas, a simplified model was proposed in this paper to calculate leaching cycle for crops that use shallow groundwater at different water table depth, considering the salt accumulation process in root zone of crops. Subsequently, leaching cycles were calculated for two study sites with soil salinity measurements. For the case study in a semi-arid irrigation area, under the current irrigation scheduling and the average rainfall condition, the calculated leaching cycle for cotton fields is 100 days for water table depth at 1 m and 140 days for water table depth at 1.5 m with the groundwater salinity maintained at 4.43 g/L; when the water table depth is greater than 2 m, the calculated leaching cycle is longer than the growing period. In another case study in an arid irrigation area with saline groundwater buried at 1.5 m deep, the calculated leaching cycle for plastic mulched and drip irrigated cotton is 78 days, applying slightly saline irrigation water with salinity of 2.81 g/L. These results indicate that managing water table depth under controlled drainage practice may increase crop use of shallow groundwater that contains dissolved salts, the rate of salinity buildup, however, is relatively slow, leaving a time window for making proper leaching schedule. The results from this study provide theoretical reference for salinity management in irrigated agricultural regions that adopt controlled drainage technique. Source

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