Modeling of nitrate and ammonium leaching and crop uptake under wastewater application considering nitrogen cycle in the soil

The proper use of domestic wastewater in agriculture sustains freshwater resources and reduces the need of chemical fertilizers. The objective of this study was to modeling of soil nitrogen dynamics and crop uptake under untreated wastewater application for irrigation taking soil nitrogen cycle into account. A two-dimensional numerical model, HYDRUS-2D, was calibrated and validated to simulate water flow, transport and distribution of nitrogen (nitrate and ammonium) in a maize farm in Mahdasht, Iran. Field experiment was conducted to measure nitrogen crop uptake and ammonium, and nitrate content in the soil profile at the upstream, middle and downstream of the irrigated furrows. The model had a good potential for simulating soil water content and nitrate and ammonium concentrations. The values of coefficient of determination ( R 2 ) for simulating soil water content, nitrate, and ammonium concentrations were 0.78, 0.80, and 0.74, respectively. Normal root means square error in simulating soil water content, nitrate, and ammonium concentrations was 6.32, 3.89, and 2.96%, respectively. The model simulated crop nitrogen uptake at harvest time as 185 kg ha −1 , which was close to the measured value (179 kg ha −1 ). A significant amount of nitrogen was leached due to the excessive use of the wastewater for irrigation. Applying different scenarios showed that the ammonium and nitrate concentrations in the wastewater fully provide the crop nitrogen requirement. Nitrate and ammonium leaching was more sensitive to the amount of irrigation than to the amount of applied fertilizer. Appropriate irrigation management could substantially reduce water deep percolation and nitrogen leaching.