FIELD–SCALE NITRATE SIMULATION

Abstract

Models are useful tools for integrating different processes involved in nitrogen transport in soil and can be usedin forecasting how a system will behave without actually making measurements in the physical system. Lately, computersimulation models have become a useful tool in understanding the transport of water and solutes through the soil into thegroundwater. Transport of water and solute in soil under field conditions is a research area of continuous interest. In this study,LEACHN, a submodule of LEACHM (leaching estimation and chemistry model), was used to simulate nitrate leaching usingan existing experimental data set collected at a land treatment site of Carterton District in New Zealand. The LEACHN modelwas calibrated with the field data collected at the site and then subjected to a sensitivity analysis against several parameters.The calibrated model was applied to the Carterton land treatment site to predict the leachate nitrate concentration in theunsaturated zone (0 to 500 mm depth) in the low, medium, and high irrigation treatments of tree and pasture plots. It wasdifficult to calibrate the model because of a lack of measured nitrate data in the root zone, nitrate movement below the rootzone to the water table was not evaluated, and the need to relate the predicted concentration in the root zone to measuredresults in the top few meters of the groundwater table. NitrateN values predicted with LEACHN were relatively sensitive tocertain soil physical and chemical properties, such as bulk density, air entry value (a), the exponent for Campbells equation(BCAM, b), mineralization rate, base temperature, and Q10, which is the factor change in rate with a 10 change intemperature. The LEACHN application to the tree and pasture plots (control plots) revealed that the cumulative drainage washigher in the pasture plots than in the tree plots. There was a drainage effect on the leachate nitrateN concentration in alltreatments of the tree and pasture plots. The model gave a good estimate of the nitrogen dynamics for different crops (treeand pasture) during different periods of the year.