Suitable Groundwater Depths for Crop Growth in Hetao Irrigation District

【Objective】 Hetao irrigation district is one of the largest surface water-irrigation districts in north China. Keeping groundwater table below a critical depth is essential to preventing salt accumulation in the root zone, and the purpose of this paper is to study the suitable groundwater depth for healthy growth of different crops. 【Method】 The experimental area is at Jiefangzha within the irrigation district. Planting structure in the area was analyzed using decision tree classification method, and groundwater depth was estimated using the Kriging interpolation method, from which we calculated the mean NDVI. The suitable groundwater depth and salinity threshold for crops at different locations were obtained from the scatter diagram of groundwater salinity and its NDVI. 【Result】 ①The suitable groundwater depth for maize at its jointing, heading and filling stages was 1.2~1.7, 1.3~1.8 m and 1.3~1.8 m, respectively, while for winter wheat, the suitable groundwater depth at its jointing, heading and filling stages was 1.1~1.6, 1.1~1.6 m and 1.2~1.7 m, respectively. The suitable groundwater depth for sunflower at its bud and filling stages was 1.1~1.6 m and 1.2~1.7 m, respectively. ②The groundwater salinity critical for crop growth is 5 g/L, with groundwater salinity in the range of TDS≤3 g/L, 35 g/L being most suitable, suitable and not suitable for crop growth, respectively. 【Conclusion】 Controlling groundwater table at suitable depths with groundwater salinity not exceeding the critical concentration is essential to improving groundwater use efficiency and sustaining crop production in Hetao Irrigation district. For the area we studied, the suitable groundwater depth varies with crops and their growth stages, but the critical groundwater salinity is approximately the same for all crops.