Modeling of Water Flow and Nitrate Transport Under Surface Drip Fertigation

The knowledge of water and nitrogen dynamics under drip irrigation is essential to the best management of dripfertigation systems, and model simulation is an effective way to obtain such knowledge. A model of water and nitrate transportin soil from a surface point source of ammonium nitrate (NH4NO3) was established and solved numerically by usingHYDRUS-2D software. In the model, selected boundary conditions were used to describe the solute transport for a mediumanda coarse-textured soil. Simulated wetting dimensions of soil volume and distributions of water content and nitrateconcentrations in soil were compared with data obtained from laboratory experiments conducted on a loam and a sandy soil.An excellent agreement was obtained between the simulated results and the measured data. Then the verified model was usedto simulate water and nitrate distributions under various initial conditions and fertigation strategies. The resultsdemonstrated that nitrate accumulated toward the boundary of the wetted volume for selected combinations of initial nitrateconcentration, application rate, volume applied, and input concentration. Nitrate distribution was greatly affected byfertigation strategies. A strategy of first applying water for one-fourth of the total irrigation time, then applying fertilizersolution for one-half of the total irrigation time, followed by applying water for the remaining one-fourth of the total irrigationtime left the most nitrate close to the source and was therefore recommended. The use of HYDRUS-2D enabled us to implementwater and nitrogen transport under surface drip fertigation and to strengthen the conclusions derived from the observations.The information obtained from the simulations is helpful in the design, operation, and management of a fertigation systemwith drip irrigation.