Determination of irrigation water quantity and its impact on crop yield and groundwater

Abstract

The objective of reservoir water allocation based on considering the ecological water demand of the downstream river has an important impact on the water allocation of each water user and the downstream ecology. Agricultural irrigation with large water consumption will directly affect crop yield. Irrigation water, as the recharge of groundwater in irrigation districts, also plays an important role in the restoration of groundwater. This research used the range of variability approach (RVA), a method of flow management considering the water demand of river ecosystems, to provide the recommended outflow range (RVA target) of the Huangbizhuang Reservoir upstream of the Shijin irrigation district. First, we used the RVA target to determine the water allocation of each water user, set 27 irrigation schemes with the water allocation of agriculture as a constraint, and used the validated AquaCrop model (seven years of field experiment data were used to calibrate AquaCrop model parameters) to evaluate the most appropriate irrigation schemes and their impact on groundwater restoration in the irrigation district. The results showed that the amount of water available for agricultural irrigation in the flood season under the RVA target was 84 mm, which was 36 mm less than the current irrigation quota (120 mm). Three irrigation schemes better than the current scheme (scheme 0) were selected, i.e., scheme 1 (irrigate 42 mm at the seedling and jointing stages), scheme 16 (irrigate 42 mm at the seedling stage), and scheme 22 (irrigate 84 mm at the seedling stage). Scheme 22 increased the yield of corn and WP (water productivity), which were 17 kg/ha and 1 kg/ha/mm higher than scheme 0, respectively, which provided the greatest increase in yield. Scheme 22 can restore 0.727 m of the groundwater table. The yield increased in scheme 16 was 4 kg/ha higher than that in scheme 0. Scheme 16 can restore 0.982 m of the groundwater table, which was the most conducive scheme for groundwater recharge. The WP of scheme 16 and scheme 1 was slightly different from that of scheme 0. There was a slight difference in biomass among the four schemes. The yield increased in scheme 1 was 12 kg/ha higher than that in scheme 0, which could restore 0.727 m of the groundwater table simultaneously, which was for a normal year. This research can provide a reference for the formulation of a local irrigation scheme to stabilize and increase summer maize yield on the premise of satisfying the ecological water demand of the river and restoring the groundwater table.