Modeling the effect of wastewater irrigation on soil salinity using a SALT-DNDC model

Wastewater has been widely reclaimed to irrigate crops where freshwater resources are scarce. Therefore, predicting the impacts of wastewater irrigation on soil moisture and soil salinity is critical for sustainable wastewater irrigation management. In this study, the denitrification-decomposition (DNDC) model was modified to couple wastewater irrigation with a water balance equation (SALT-DNDC). Secondly, the SALT-DNDC model was verified against the measured soil moisture, temperature, and nitrous oxide emission during the barley-growing season at Lethbridge, Alberta, Canada. Third, the SALT-DNDC model was used to predict the effects of one-time and split wastewater irrigation with varying quantity and quality on transpiration and soil salinity. The results showed that split irrigation of wastewater with an electrical conductivity of 6 dS m⁻¹ reduced the peak soil salinity from 52–55 dS m⁻¹ to a range of 8–20 dS m⁻¹, compared to one-time irrigation. Therefore, the split irrigation of wastewater could substantially reduce peak soil salinity. In this regard, optimal split wastewater irrigation with elevated salt concentration can limit soil salinity to acceptable salt tolerance levels for crop growth. The SALT-DNDC model can simulate dynamics of split irrigation wastewater and offers a new tool for assessing the effects of wastewater reuse on soil salinity.