Treated wastewater (TWW) is a key source to secure agriculture in Palestine. Achieving a good water quality does not only imply its immediate reuse in irrigated agriculture but also a long-term conservation of soil and groundwater quality, marked by the complex mechanisms that correlate the soil, water, plant and atmosphere. Therefore, monitoring and modeling are combined in this study that primarily aims at the estimation of the soil water and nitrate fluxes, with a view to reducing deep percolation fluxes in a case study in Beit Dajan-Palestine. The investigated area (0.349Ha) cultivated with citrus, was irrigated with TWW in the last 5 years.
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Soil nitrogen concentration and water content data were collected from March to August 2021 to calibrate Hydrus-1D model, then the water and nitrate fluxes were retrieved for 2019 and 2020 under two TWW irrigation scenarios: 1) farmer demand (F) where irrigation volumes are delivered twice per week; 2) model demand (M) based on an irrigation frequency of 1 event per week scheduled in order to balance a dual nitrate source: i) nitrified ammonium 〖N-NH〗_4^+; and ii) nitrate 〖N-N0〗_3^-, both simultaneously supplied with TWW. For 2021, the measured soil electrical conductivity, σw, showed no salinity risk with an average value of 1.07 dS/m (low salinity < 2dS/m). However, a high level of total N in the soil exceeding 0.5% (standard value 0.1-0.2%) and a low concentration of N in the leaves (below 1%) suggesting a low assimilation, are observed. In addition, the comparison between simulated and measured soil variables show that 1D-Hydrus model was able to follow the temporal variation of the monitored data, with some overestimation of the measured data during the simulation period. M scenario also showed a decrease of nitrates leaching by 33% as compared to F scenario.