Assessing the Effects of Drip Irrigation System Uniformity and Spatial Variability in Soil on Nitrate Leaching through Simulation

Abstract

Abstract. Both drip system uniformity and spatial variability in soil are important factors affecting deep percolation and nitrate leaching. The effects of the two factors on deep percolation and nitrate leaching at a typical irrigation quota for maize were assessed using the water and solute transport model HYDRUS-2D. The evaluation of the influence of soil variability on nitrate leaching using a global sensitivity analysis 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 five Christiansen uniformity coefficients (CU) of 50%, 60%, 70%, 80%, and 95% under different variabilities of the four soil properties mentioned above. The results indicated that nitrate leaching decreased slightly with increase in CU, while it increased considerably with spatial variability of soil properties. For a typical irrigation event of maize, the nitrate nitrogen (NO 3 -N) leaching rate decreased from 2.0 to 1.1 kg ha -1 and from 6.2 to 5.5 kg ha -1 as CU increased from 60% to 95% for an assumed homogeneous field and a field having medium variability, respectively. A considerable increase of NO 3 -N leaching rate was observed as the system uniformity decreased from 60% to 50%, although the effect of system uniformity on nitrate leaching was damped by the spatial variability in the soil. Drip irrigation system uniformities as low as 60%, which are lower than the current standards, might be used without negatively affecting nitrate leaching.