Drip irrigation enhances shallow groundwater contribution to crop water consumption in an arid area

Shallow groundwater plays a key role in agro-hydrological processes of arid areas. Groundwater often supplies a necessary part of the water requirement of crops and surrounding native vegetation, such as groundwater-dependent ecosystems. However, the impact of water-saving irrigation on cropland water balance, such as the contribution of shallow groundwater to field evapotranspiration, requires further investigation. Increased understanding of quantitative evaluation of field-scale water productivity under different irrigation methods aids policy and decision-making. In this study, high-resolution water table depth and soil water content in field maize were monitored under conditions of flood irrigation (FI) and drip irrigation (DI), respectively. Groundwater evapotranspiration (ETg) was estimated by the combination of the water table fluctuation method and an empirical groundwater-soil-atmosphere continuum model. The results indicate that daily ETg at different growth stages varies under the two irrigation methods. Between two consecutive irrigation events of the FI site, daily ETg rate increases from zero to greater than that of the DI site. Maize under DI steadily consumes more groundwater than FI, accounting for 16.4% and 14.5% of ETa, respectively. Overall, FI recharges groundwater, whereas DI extracts water from shallow groundwater. The yield under DI increases compared with that under FI, with less ETa (526mm) compared with FI (578mm), and irrigation water productivity improves from 3.51kgm(-3) (FI) to 4.58kgm(-3) (DI) through reducing deep drainage and soil evaporation by DI. These results highlight the critical role of irrigation method and groundwater on crop water consumption and productivity. This study provides important information to aid the development of agricultural irrigation schemes in arid areas with shallow groundwater.