Assessment and Simulation of Water and Nitrogen Transfer Under Furrow Irrigation.
Z. Popova, N.Poushkarov Institute of Soul Science, 7 Shosse Bankya, Sofia, 1080, Bulgaria
This communication deals with the problem of risks relative to nitrate leaching under furrow irrigation depending on the technique of water and fertiliser application. The objective is to: 1) calibrate the water and nitrogen transfer components of Hydrus-2D model (Simunek et al.1999) for every furrow irrigation (EFI) and alternative furrow irrigation (AFI) on Chromic Luvisol in Sofia region; 2) to use the calibrated model to assess the impact of application depth distribution along the furrow length on deep percolation and nitrate leaching for EFI and AFI practices. Six-step operative procedure is elaborated for model calibration on Chromic Luvisol (Sofia region, Bulgaria). Detailed data, as water and nitrogen content profiles under the ridge and the furrow bed, variables at the boundaries of the system (as precipitation, drainage and nitrogen leaching, plant uptake) observed in cropped lysimeters are used to verify mathematical accuracy. In a first calibration step, the hydrological components of the soil are derived by regression of laboratory and field water retention data. Obtained parameters of Van Genuchten water retention curve are adjusted by comparing simulated soil water, pressure head and drainage with field observations. Every furrow irrigation is approximated by a one-dimensional (1D) water flow in step (ii) while step (iii) is made when a two-dimensional (2D) flow is adopted. Step iv is made of data from the trials in AFI lysimeter. The next two calibration steps (v) and (vi) are made of observed data relative to the fate of nitrogen (N) in EFI and AFI lysimeters. Calibrated model predictions of soil nitrogen concentrations and nitrate leaching are in agreement with the observed values. The calibrated model is used to predict the impact of application depth distribution along the furrow length on deep percolation and N-leaching in case of EFI and AFI practices on Chromic Luvisol.