A field scale model of soil drainage and nitrate leaching for application in nitrate vulnerable zones

We present a new conceptual model of nitrate leaching from structured soils at the field scale that is readily parameterised from nationally available soil datasets. The model explicitly captures the effects of incomplete equilibration between mobile and immobile waters, and lateral flow in the presence of tile drainage. The derivation of parameters and model validation are illustrated by the application of the model to experimental data sets from intensively monitored soil drainage systems at the ADAS Gleadthorpe, Boxworth, Brimstone and Rosemaund field experimentation sites in the UK. Results of the validation show that the model is capable of simulating the drain flow hydrographs observed on structured soils and also capturing the variations in over-winter leaching occurring on both unstructured and structured soils (respective r2 of 0.58 and 0.49). The model also captures some of the daily variations in nitrate concentrations characteristic of structured soils.