Assessing Salinity Leaching Efficiency in Three Soils by the HYDRUS-1D and -2D Simulations

Salinity leaching is necessary to sustain agricultural production in irrigated croplands. Improving salinity leaching efficiency not only conserves water but also reduces groundwater contamination. Current leaching requirement (LR) calculations are based on steady-state and one-dimensional (1D) approaches, and consequently, this LR concept may not be applicable to drip irrigation (approximately 2D), which is becoming more common due to its higher water use efficiency. The aims of this study were to assess the salinity leaching fraction (LF) in clay, loam, and sand soils under 1D (to mimic sprinkler irrigation) and 2D (to mimic drip irrigation) transient conditions with a numerical model (HYDRUS). Water applications used the actual irrigation scheme in an almond orchard located in central California without considering precipitation. Model simulations showed that soil salinity at the lower boundary (depth of 150 cm) reached steady-state in 10 years in HYDRUS-1D simulations. The leaching fractions calculated from the ratio of drainage-water depth to irrigation-water depth (LFw = D-dw/D-tw,) and irrigation-water salinity to drainage-water salinity (LFEC = ECtw/ECdw) from HYDRUS-1D were similar among different textured soils. However, they were much higher under drip irrigation (2D) than under sprinkler irrigation (1D) when the same amount of water was applied, and LFEC values were much greater than the LFw values under 2D simulations. Salt balance (SB) and leaching efficiency (LE) indicated that sprinkler irrigation (1D) is more effective for salinity leaching than drip irrigation (2D). To improve salinity leaching efficiency, further evaluation of LRs under drip irrigation is needed.