Drainage and salinity assessment in the Huinong Canal Irrigation District, Ningxia, China

In the Huinong Canal Irrigation District, Ningxia, China, annually almost half of the amount of irrigation water, which is supplied from the Yellow River, is drained back to the river through an open drainage system. Waterlogging and salinization occur in parts of the irrigated area and part of the water drains to the surrounding desert. While 85-90 % of inflow to the area is irrigation water there are good possibilities for water saving. To analyse water movement at field level and resulting drainage needs, from autumn 1998 until spring 2001 observations were made in two experimental areas: Pingluo and Huinong. The data were used for the calibration and validation of three computer models: SWAP, MODFLOW and DUFLOW. Different scenarios of water and salt behaviour in the unsaturated and saturated zone were simulated, as well as the flow through one of the main drains. The effects of various irrigation amounts and groundwater tables on crop growth, percolation and drainage needs were analysed. The present average irrigation water application during the growing season is 630 mm. On average 15 % of the supplied water (665 million m(3) yr(-1)) remains in the area. This is mainly irrigation water that was not used by the crops and did not reach the drainage system. It was found that an irrigation level of 75 % of the present practice with a groundwater table of 1.0 m below the surface during the growing season gave the best results. Under such a practice the soil salinity will fluctuate around 3-3.5 dS m(-1) resulting in a good growth of wheat and a yield reduction for maize of about 20 %. When adequate amounts of irrigation water are supplied in combination with local drainage improvements, the areas with middle and low-yielding crops can be reduced, as well as the area of wasteland. Copyright (c) 2005 John Wiley & Sons, Ltd.