Assessing the effects of drip irrigation system uniformity and spatial variability in soil on nitrate leaching through simulation

摘要

Both drip irrigation system uniformity and spatial variability in soil are important factors affecting deep percolation and nitrate leaching. The effects of drip irrigation system uniformity and spatial variability in soil on deep percolation and nitrate leaching for a typical irrigation quota of maize were assessed using a water and solute transport model HYDRUS-2D. The evaluation on the influence of the variability in soil on nitrate leaching by using a global analysts approach demonstrated that the spatial variabilities of saturated hydraulic conductivity, saturated water content, and initial water and nitrate contents in soil imposed significant effects on nitrate leaching. Deep percolation and nitrate leaching were then simulated under four Christiansen uniformity coefficients (CU) of 50%, 60%, 80%, and 95% under different variabilities of the four soil properties ahovementioned in soil. The results indicated that nitrate leaching decreased slightly with CU while it increased significantly with spatial variability in soil properties. For a typical irrigation event of maize in the North China Plain, the nitrate leaching decreased from 1.92 to 1. 13 kg ha'1 andfrom 4.82 to 4.65 kg ha'1 as CU increasedfrom 60% to 95% for a homogeneous field anda field having medium variability, respectively. A considerable increase of nitrate leaching was observed as the system uniformity decreased from 60% to 50% for a field having medium variability, although the effects of system uniformity on nitrate leaching was damped by the spatial variability in soil. The drip system uniformities that are lower than the values recommended by the current standards might be used while an extremely low drip uniformity of less than 60% is not recommended.