Groundwater Depth and Irrigation Amount Affect Water Exchange between Groundwater and Soil Water in Hetao Irrigation District

Abstract

【Background and Objective】 Hetao irrigation district is one of the three mega-irrigation districts relying on Yellow river water for irrigation in China. However, the reduced water supply for the district to take for the river in the past decade has promoted the region to develop water-saving irrigation. Different agronomic and engineering methods have been developed, and the aim of this paper is to elucidate how to improve groundwater usage by crops by manipulating irrigation amount in regions with different groundwater depths. 【Method】 The experiment was conducted over the district by irrigating the crops three time during their growth season, with the irrigation amount at each growth stage varying from 90 to 135 mm. Added to this is a further irrigation in autumn with an irrigation amount of 300mm. The average annual groundwater depth in the experimental regions varied from 1.8 m to 2.0 m. In each treatment, we measured the change in soil water content and groundwater table before and after the irrigation. 【Result】 Average water content in the 0~60 cm soil changed significantly following irrigation, regardless of the irrigation amount. The first two irrigations in the crop growth season replenished the water in the tillage layer, while in the third irrigation 25% of the irrigation water leached to the subsoils. Overall, the larger the irrigation amount was, the more water would leach into the groundwater. The proportion of irrigation water leached to the groundwater increased with irrigation amount when the average annual groundwater depth was the same, and decreased with the groundwater depth when the irrigation amount was the same. 【Conclusion】 For areas with annual groundwater depth of 1.8 m, irrigating 90 mm in each of the three irrigations during the crop growth season, together with a 300 mm autumn irrigation, can significantly reduce irrigation water leaching and increase groundwater usage by the crops.

Keywords

• irrigation amount
• groundwater depth
• water exchange
• soil water leaching