With the wide application of drip irrigation under mulch in semi-arid agricultural region in China, it not only improves agricultural water efficiency, but also affects formation of groundwater and the mechanism of water infiltration to a certain extent. This paper takes the typical semi-arid agricultural region in China as the research object. The movement of soil water under the three types of underlying surface was simulated by the Hydrus-2D model for the quantitative analysis of groundwater recharge. The influence of drip irrigation under mulch on groundwater infiltration depth and cumulative infiltration amount under different level years was simulated. Taking normal flow year as an example, the simulated results showed that the maximum infiltration depth of drip irrigation under mulch reached 250 cm, which was greater than that of border irrigation (138 cm) and bare area (158 cm). The cumulative infiltration amount of drip irrigation under mulch at 80 cm, 120, 140 and 200 cm was respectively 1,484.8 m3/hm2, 686.3 m3/hm2, 554.1 m3/hm2 and 238.1 m3/hm2, which were greater than that of border irrigation and bare land at the same depth. The results proved that drip irrigation under mulch could increase the infiltration depth and cumulative infiltration amount, which was beneficial to groundwater recharge in semi-arid agricultural region of China.
In the agricultural region of the Xiliao River Plain, drip irrigation under mulch has been widely implemented. It not only saves irrigation water, but also changes the structure of the underlying surface of agricultural land, which affects the local hydrological cycle to a certain extent, and makes the process of nitrogen transportation in soil with new characteristics. This study analyzed the distribution of NH4-N, NO3-N, and NO2-N in different soil depths during the whole growth period under three underlying surface conditions, including drip irrigation under mulch, border irrigation, and bare area through field in-situ observation experiment, and analyzed the influence of drip irrigation under mulch on nitrogen transport in deep soil layers. The results showed that under the soil properties of the experimental area, drip irrigation under mulch creates more water to enter the deep soil layers, which was beneficial to alleviate the downward trend of local groundwater level to a certain extent. The average content of NH4-N and NO3-N under drip irrigation under mulch was higher than that under border irrigation. The average content of NH4-N under drip irrigation under mulch was 1.24 mg.kg-1 in soil depths of 80-300 cm, and 0.97 mg.kg-1 under border irrigation. The average content of NO3-N under drip irrigation under mulch was 2.73 mg.kg-1 in soil depths of 80-300 cm, and 1.99 mg.kg-1 under border irrigation. The increment of NH4-N and NO3-N distribution in deep soil layers under drip irrigation under mulch was greater than that under border irrigation, and the increment of NO3-N content is significantly greater than that under border irrigation. Soil water content has a significant impact on the contents of NH4-N and NO3-N. It indicated that compared with traditional border irrigation, drip irrigation under mulch was beneficial to alleviate the downward trend of local groundwater, but it would increase the risk of nitrogen pollution in local groundwater.
The imbalance between exploitation and recharge and the yearly decline in water tables is a common water resource problem in semi-arid areas in China. To ensure the sustainable use of groundwater and the stability of the regional hydrological cycle, a reasonable groundwater control table need to be determined to achieve a balance between groundwater exploitation and recharge. Based on the characteristics of the vertical hydrological cycle in semi-arid irrigation areas, this paper used a combination of in situ field experiments and software simulations to calculate the groundwater infiltration recharge under three types of subsurface conditions, namely, drip irrigation under mulch, border irrigation, and bare area, and to analyze the relationship between groundwater infiltration recharge and groundwater table. Based on the relationship between groundwater recharge and discharge, the critical groundwater depth of maintaining exploitation and recharge balance (CGDM) for drip irrigation under mulch was calculated to be 131.52-187.15 cm, and the critical groundwater depth of disrupting exploitation and recharge balance (CGDD) was 307.66-363.67 cm. For border irrigation, the CGDM was 80.00-84.34 cm and the CGDD was 198.87-248.44 cm. It also proposed a groundwater table management strategy to address the risk of imbalance in regional groundwater exploitation and recharge. The critical groundwater depth of controlling risk management (CGDC) can be used for regional groundwater management and guidance for agricultural irrigation, providing technical support for achieving regional groundwater exploitation and recharge balance and maintaining a stable hydrological cycle.
The imbalance between exploitation and recharge and the yearly decline in water tables is a common water resource problem in semi-arid areas in China. To ensure the sustainable use of groundwater and the stability of the regional hydrological cycle, a reasonable groundwater control table need to be determined to achieve a balance between groundwater exploitation and recharge. Based on the characteristics of the vertical hydrological cycle in semi-arid irrigation areas, this paper used a combination of in situ field experiments and software simulations to calculate the groundwater infiltration recharge under three types of subsurface conditions, namely, drip irrigation under mulch, border irrigation, and bare area, and to analyze the relationship between groundwater infiltration recharge and groundwater table. Based on the relationship between groundwater recharge and discharge, the critical groundwater depth of maintaining exploitation and recharge balance (CGDM) for drip irrigation under mulch was calculated to be 131.52-187.15 cm, and the critical groundwater depth of disrupting exploitation and recharge balance (CGDD) was 307.66-363.67 cm. For border irrigation, the CGDM was 80.00-84.34 cm and the CGDD was 198.87-248.44 cm. It also proposed a groundwater table management strategy to address the risk of imbalance in regional groundwater exploitation and recharge. The critical groundwater depth of controlling risk management (CGDC) can be used for regional groundwater management and guidance for agricultural irrigation, providing technical support for achieving regional groundwater exploitation and recharge balance and maintaining a stable hydrological cycle.
Water scarcity has been a critical constraint to economic development in semi-arid areas of China, so optimizing irrigation scheduling has become essential. This study obtained quantitative relationships between crop yield, crop water consumption, and irrigation quantity based on the Hydrus-2D and Stewart models. Different irrigation scheduling scenarios were evaluated to obtain the best irrigation scheduling based on the principle of simultaneous water conservation and crop productivity improvement with the evaluation indicators of crop yield, water use efficiency (WUE), irrigation water use efficiency (IWUE), and Critic-Topsis method. Taking drip irrigation under mulch as an example, the problem of optimizing the irrigation scheduling for different typical years was calculated. The optimization results showed that in the wet, normal, dry, and very dry years the annual irrigation quantity should be 49.68 mm, 49.68 mm, 85.38 mm, and 123.72 mm, when the WUE as well as IWUE, increases significantly, which had less impact on the crop yield and can save irrigation quantity by 30.00%, 30.00%, 35.00%, 27.00%. This study used Hydrus-2D to make a new attempt in irrigation scheduling optimization, giving full play to the model's high accuracy in soil water transport simulation and flexibility in boundary condition simulation. The optimization results can provide a reference for achieving accurate control of irrigation quantity during the crop growth period and reasonable irrigation scheduling formulation for regional crops.
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