Simulating soil water flow and nitrogen dynamics in a sunflower field irrigated with reclaimed wastewater M.H. Rahil, V.Z. Antonopoulos * Department of Hydraulics, Soil Science and Agriculture Engineering, School of Agriculture, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece 1. Introduction The reuse of treated domestic wastewater for irrigation is considered to be beneficial for crop production, and due to its nitrogen and phosphorus content, it can help to reduce the requirements for commercial fertilizers. During the last two decades the effluent of wastewater treatment plants has become part of water resources and has been incorporated in water resources management projects. However, under certain conditions, this type of water if not well managed, can have negative impacts on cultivated crops and soils, particularly on soil salinity and sodicity, and may pollute groundwater, as a result of high nitrogen concentration of most treated wastewater (Vazquez-Montiel et al., 1995). The wastewater treatment plant of Thessaloniki city (WTPT), in northern Greece, produces approximately 150,000 m 3 day 1 of treated wastewater, which is disposed into the Thermaikos Gulf of the northern Aegean Sea. The WTPT is located at the eastern boundary of Thessaloniki plain, which is one of the largest irrigated areas in the country, covering 78,000 ha. The reuse of treated wastewater of WTPT in agriculture is a challenge for many reasons. The first is the conservation of water resources of the area and the release of fresh water for drinking and municipal uses. The second is the protection of Thermaikos Gulf from euthrophication and pollution by constituents in the wastewater. Improvement of irrigation and nitrogen application man- agement during the growing period can be achieved using mathematical models. Several one dimensional models have been proposed in the literature to simulate water flow, solute transport, and crop uptake of water and nutrients, as well as biological transformation of nitrogen in the soil (Bergstrom et al., 1991; Hutson and Wagenet, 1991; Jarvis, 1995; Gabrielle and Kengni, 1996; Lafolie et al., 1997; Diekkruger et al., 1995; Hutson, 2000; Rinaldi, 2001; Antonopoulos, 2001). Most models however, focus on fertilizer application and nitrate leaching. agricultural water management 92 (2007) 142–150 article info Article history: Accepted 8 May 2007 Published on line 30 July 2007 Keywords: Simulation Water content Nitrogen balance Wastewater reuse Nitrogen leaching abstract Soil water flow and nitrogen dynamics were simulated in sunflower field during and after the growing period, in Northern Greece. Soil water and nitrogen dynamics were evaluated using a one-dimensional simulation model based on the Galerkin finite element method. We examined the effects of irrigation with reclaimed wastewater and nitrogen fertilizer applications on plant growth, water and nitrogen distribution in the soil profile, water and nitrogen balance components and nitrogen leaching to groundwater. The model simulated the temporal variation of soil water content with reasonable accuracy. However, an over estimation of the measured data was observed during the simulation period. Relatively good agreement was found between the simulated and measured NH 4 -N and NO 3 -N concentra- tions over time and depth, whereas fluctuations at greater depths were relatively small. Most of the cumulative nitrate-N leaching (44.7 kg N ha 1 ) occurred during the winter. # 2007 Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +30 2310 998745; fax: +30 2310 998767. E-mail address: vasanton@agro.auth.gr (V.Z. Antonopoulos). available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/agwat 0378-3774/$ – see front matter # 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.agwat.2007.05.019