Effect of Drip Irrigation Under Mulch on Nitrogen Transport in Deep Soil Layers in an Agricultural Region of the Xiliao River Plain, 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.