Simulation of nitrate leaching under varying drip system uniformities and precipitation patterns during the growing season of maize in the North China Plain

Drip irrigation has been recognized as an efficient irrigation method to improve water and nitrogen use efficiency. However, less-than-optimum management of drip system may cause deep percolation and nitrate leaching. The effects of drip system uniformity and precipitation on deep percolation and nitrate leaching under maize in a subhumid region were evaluated using a water and solute transport model HYDRUS-2D. Field experiment data on the spatial and temporal distribution of water and nitrate content during the growing seasons (2011 and 2012) of maize were collected to calibrate and validate the model. The validation indicated that the model performed well with an RMSE (root mean square error) value of 0.03–0.05 cm3 cm−3 for soil water content and 2.6–8.9 mg kg−1 for nitrate content during the growing season. Then, deep percolation and nitrate leaching were simulated under varying drip system uniformities and precipitation patterns. In the simulations, three Christiansen uniformity coefficients (CU) of 60%, 80%, and 95% were tested under typical precipitation patterns of dry, normal, and wet growing seasons that were determined from 32 years (1980–2011) of meteorological data. The result demonstrated that deep percolation and nitrate leaching most likely occurred following a heavy precipitation event, whereas slight deep percolation was observed following an irrigation event. The averaged seasonal nitrate leaching over the three drip system uniformities was 34.1 kg ha−1 for dry growing seasons (precipitation less than 287 mm), 60.3 kg ha−1 for normal seasons (precipitation from 287 to 480 mm), and 109.3 kg ha−1 for the wet seasons (precipitation greater than 480 mm). Drip system uniformity had a more significant effect on nitrate leaching during dry seasons than during normal and wet seasons. A correlation analysis between seasonal nitrate leaching and precipitation, irrigation, and drip system uniformity revealed that it was most significantly affected by seasonal rainfall, followed by system uniformity. Both the amount of precipitation and the temporal distribution of precipitation during the growing season of crop should therefore be considered when the target drip irrigation uniformity is determined.