Simulation of soil water dynamics for uncropped ridges and furrows under irrigation conditions

Zhang, Y., Wu, P., Zhao, X. and Wang, Z. 2013. Simulation of soil water dynamics for uncropped ridges and furrows under irrigation conditions. Can. J. Soil Sci. 93: 85-98. The ridge-furrow planting system combined with furrow irrigation can effectively increase soil moisture storage and improve water use efficiency in the semi-arid region of China. The precise soil water dynamics in ridge-furrow systems must be known in order to properly design ridge-furrow geometry and improve irrigation uniformity while reducing deep water percolation. The objective of this study was to investigate soil water distribution in the cross-sectional ridge-furrow infiltration, through laboratory experiments and numerical simulations. Six experimental treatments with three soil types (silty clay loam, silt loam, and sandy loam) were tested to monitor both soil water movement and cumulative infiltration in rectangular soil chambers. The HYDRUS-2D model was calibrated and experimentally validated to simulate soil water dynamics. The root mean square error (RMSE) and coefficient of determination (R-2) provide a satisfactory quantitative comparison of the goodness-of-fit between observed and simulated cumulative infiltration. The optimized parameters were accurate and the observed and simulated values were very close, which demonstrated HYDRUS-2D as a reliable tool for accurately simulating soil water movement and applied water volume in ridge-furrow irrigation system. In finer soil, the wetted vertical and horizontal distances were equal and soil water distribution was more uniform than that in coarser soil. A high potential of deep water percolation was produced in sandy loam soil. Cumulative infiltration decreased with the increase of initial soil water content, whereas the volume of wetted soil increased with the increase of initial soil water content. Narrow furrows for crops with deep rooting depth and wide furrows for crops with shallow rooting depth were selected in irrigation design. The 40 cm furrow size and higher furrow water depth (water level) were recommended in a ridge-furrow irrigation system.