WANG Zhen, LI Jiu-sheng, LI Yan-feng (State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin, China Institute of Water Resources and Hydropower Research, Beijing 100038, China)

Abstract: It is of importance to consider the leaching of water and nitrogen in designing, operation and management of drip irrigation systems. A model simulating the transport of water and nitrate in soil was established and solved numerically by using the HYDRUS-2D package. The local sensitivity analysis and global sensitivity analysis were carried out over the model to evaluate the influence of the spatial variability of soil hydraulic parameters, initial water content and nitrate nitrogen content on water leakage and nitrate leaching for a sandy loam soil under drip irrigation. The results indicate that the water leakage ratio and nitrate leaching ratio decreased greatly with an increase of saturated water content, while the ratios increased steadily with an increase of initial soil water content. For the sandy loam soil with a low spatial variability, the majority of the variability of the water leakage and nitrate leaching can attribute to the spatial variability of initial and saturated water content and saturated hydraulic conductivity. However, water leakage ratio and nitrate leaching ratio are mainly controlled by the initial water and nitrate content when the spatial variability of soil reached a medium level. The potential risk of nitrate leaching might be underestimated for a soil with medium spatial variability if the soil variability was neglected. It is therefore suggested that the spatial variability of soil should be considered when water leakage and nitrate leaching was assessed for a soil with a medium to high variability level.

Key words: drip irrigation, water leakage, nitrate leaching, soil parameters, spatial variability, sensitivity analysis

Published in: Journal of Hydraulic Engineering, Vol. 44, No. 3, 2013