Predicting soil water, tile drainage, and runoff in a mole-tile drained soil

Abstract

There has been considerable intensification of agriculture on mole-tile drained soils in New Zealand. Management techniques and tools are needed for predicting and understanding water and nutrient transport. While simple water balance models have been effective in estimating soil water deficit, such models cannot differentiate between the different water loss mechanisms. More complex water-transport models include the ability to predict the flow of water and nutrients through mole-tile drainage systems but none have yet been applied, or tested, under New Zealand conditions. Here we test such a model against existing data. The simulation model APSIM was used to estimate soil water extraction by pasture, slow drainage through the fragipan, mole-tile drainage, surface runoff, and evaporation from the soil surface of the Tokomaru silt loam. Soil hydraulic properties were derived from the literature. Comparison was made against previously published data on soil water deficit, tile drainage, and surface runoff. APSIM's predictions of soil water deficit compared well against much of the available data. The exception to this was during a period of exceptionally dry soil conditions when the model predicted a lower soil water deficit than indicated by the data. There was excellent agreement between the simulated and measured drainage, as well as reasonable agreement of measured and modelled surface runoff on a cumulative basis, although there was some deviation when considered on an event basis. © 2007 Taylor & Francis Group, LLC.