Irrigation with Treated Wastewater (TWW) is a well-known agricultural practice in Palestine. Being a source of water and nutrients, long term use of TWW can lead to imbalances that affect plant development, soil, and groundwater quality. Consequently, irrigation frequency and interval should be properly scheduled, especially when Fertilizers and Salts (FS-TWW) cannot be separated from water. A case study in Beit Dajan cultivated with citrus and irrigated with TWW was selected to assess TWW effects on the soil and on root uptake.
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To this purpose, two-year (2018-2019) simulations were performed using Hydrus- 1D physically-based model and generating two FS-TWW irrigation scenarios: 1) non-optimized salt supply (NONOPT-FS-TWW) where irrigation volumes fully satisfied crop evapotranspiration demand: 2) optimized salt supply (OPT-FS-TWW) accounting for crop evapotranspiration and respecting allowable thresholds of soil solution electrical conductivity (ECe) by assuming an average soil salinity tolerance in the root zone. Soil water movement, ECe and 〖N-N0〗_3^-, 〖N-NH〗_4^+ concentrations were simulated considering averaged ten-yearly climate data and using soil and water quality analyses. Under OPT-FS-TWW scenario, the effects of salinity stress on water and nutrient uptake decreased, improving soil nitrate adsorption by 36% and reducing by 30% soil salinity in the root zone and by13% water and nutrient fluxes at 60cm depth as compared to NON-OPT-FS-TWW scenario. The results obtained when considering ECe as an additional variable to schedule irrigation with TWW encourage the validation of Hydrus-1D model using an evolution of water and salt distribution measurements.
