title: Nitrate fluxes to groundwater under citrus orchards in a Mediterranean climate: observations, calibrated models, simulations and agro-hydrological conclusions.
abstract: Nitrate contamination of groundwater under land used for intensive-agriculture is probably the most worrisome agro-hydrological sustainability problem worldwide. Vadose-zone samples from 0 to 9 m depth under citrus orchards overlying an unconfined aquifer were analyzed for variables controlling water flow and the fate and transport of nitrogen fertilizers. Steady-state estimates of water and NO3-N fluxes to groundwater were found to vary spatially in the ranges of 90-330 mm yr(-1) and 50-220 kg ha(-1) yr(-1), respectively. Calibration of transient models to two selected vadose-zone profiles required limiting the concentration of NO3-N in the solution that is taken up by the roots to 30 mg L(-1). Results of an independent lysimeter experiment showed a similar nitrogen-uptake regime. Simulations of past conditions revealed a significant correlation between NO3-N flux to groundwater and the previous year's precipitation. Simulations of different nitrogen-application rates showed that using half of the nitrogen fertilizer added to the irrigation water by farmers would reduce average NO3-N flux to groundwater by 70%, decrease root nitrogen uptake by 20% and reduce the average pore water NO3-N concentration in the deep vadose zone to below the Israeli drinking water standard; hence this rate of nitrogen application was found to be agro-hydrologically sustainable. Beyond the investigation of nitrate fluxes to groundwater under citrus orchards and the interesting case-study aspects, this work demonstrates a methodology that enables skillful decisions concerning joint sustainability of both the water resource and agricultural production in a common environmental setting.
authors.affiliation: Institute of Soil, Water and Environmental Sciences, The Volcani Center, Agricultural Research Organization, POB 6, Bet Dagan 50250, Israel. daniel@volcani.agri.gov.il
authors.forename: Daniel
authors.initials: D
authors.lastname: Kurtzman
authors.forename: Roi H
authors.initials: RH
authors.lastname: Shapira
authors.forename: Asher
authors.initials: A
authors.lastname: Bar-Tal
authors.forename: Pinchas
authors.initials: P
authors.lastname: Fine
authors.forename: David
authors.initials: D
authors.lastname: Russo
mesh_terms: D000383:Agriculture; D002957:Citrus; D004784:Environmental Monitoring; D060587:Groundwater; D007557:Israel; D008962:Models, Theoretical; D009566:Nitrates / Q000032:analysis*; D014872:Water Movements; D014874:Water Pollutants, Chemical / Q000032:analysis*; D014876:Water Pollution / Q000517:prevention & control
chemical_list: D009566:Nitrates; D014874:Water Pollutants, Chemical
keywords: Agro-hydrology; Groundwater contamination; Model simulation; Nitrate; Vadose zone