Modeling nitrate movement in sugarbeet soils under flood and drip irrigation

Nitrate (NO3) contamination is a continued global concern in many sugarbeet growing areas under flood irrigation. Use of drip irrigation can offer an alternative pollution control technology. With the objectives of comparing the effects of drip and flood irrigation on NO3 movement in sugarbeet soils, a computer simulation study was conducted using a transport and irrigation model and the simulation results were compared with field data. Four irrigation treatments, including 20% (Drip 1), 35% (Drip 2), 50% (Drip 3), and 65% (Flood) water depletion of field capacity, were tested. At any given time, soil NO, concentrations followed the order of Drip1 > Drip2 > Drip3 >> Flood. The higher irrigation frequency with minimal quantity of water corresponding to the least depletion percentage was found to be the best scheduling scheme for retaining NO3 in soils. Throughout the irrigation period, greater (an average of 5 times) concentration-depth gradients for all three drip regimes, as compared to flood, were predicted by the simulations, indicating lower NO3 loss with drip at any profile-depth. Kinetic analysis indicated that the rate of NO3 movement under flood irrigation was 2 to 3.5 times faster than with the three drip regimes. The slowest leaching rate for Drip1 was an indication of longer residence phase of NO3 in soils during the growing season. As compared to flood, the half-life of NO3 was nearly 3.5, 2.5, and 2.0 times greater under Drip1, Drip2, and Drip3, respectively. Simulations predicted the residual soil NO3 (RSN) followed the order of Drip1 > Drip2 > Drip3 > Flood. Higher RSN values for the drip regimes suggested less NO3 depletion and greater NO3 availability as basal dose for the following crop. Simulation results were not significantly different from the actual data on soil NO3 content and yield ratios obtained with field experiments (P less than or equal to 0.05). This indicated that the simulation results could be utilized to understand in situ behavior of NO3, which would be otherwise difficult or expensive to determine directly by field sampling and characterization.