Effect of field groundwater table control on water and salinity balance and crop yield in the Qingtongxia Irrigation District, China

The Qingtongxia Irrigation District (QID) is one of the key agricultural bases in the Yellow River Basin. It is located in the upstream part of the Yellow River in the north of China and covers about 350 000 ha of farmland. The climate in the district is arid and semi-arid. The annual average precipitation is about 200 mm. Water shortage is one of the main restrictions on agricultural development. In recent years, large amounts of water have been drawn from the Yellow River, which not only contributes to the severity of water shortages in the middle and downstream part of the Yellow River Basin, but also leads to the rise of the groundwater table and related waterlogging and salinization of the farmland. This article focuses on the analysis of the effects of field groundwater table control under different irrigation water amounts on the soil water and salinity content and on relative crop yield. Two experimental areas, Pingluo and Huinong, were selected to collect the required field data. The agro-hydrological model SWAP was used to analyse the water flow and salt transport for different groundwater table and irrigation scenarios. Six scenarios, which resulted from two groundwater table regimes combined with three irrigation amounts, were simulated. The groundwater table regimes represent the present and future target groundwater table situation and the three irrigation amounts represent different water-saving options. Waterlogged land is also simulated. The results show that: High regional groundwater tables are the main reason for the large amount of drainage water and low crop yield. Due to the regional high groundwater table, reducing irrigation amounts in the field without lowering the field groundwater table will not lead to a large reduction of drainage water, and will cause a further reduction in crop yield. The salinity storage in the soil profile at the end of the growing season will increase when the irrigation amount is reduced, and when the groundwater table is lower. But the increase is very small. To lower the field groundwater to the target water table is an effective way to increase crop yield. Copyright (C) 2004 John Wiley Sons, Ltd.