CRACK-NP, development of a model for predicting pollutant transport in cracking clay soils

In cracking clay soils the movement of water and solutes is greatly influenced by the arrangement of cracks and aggregates in the soil profile. It is essential that a model to simulate leaching from clay soils takes into account the routes of water movement and the interaction between water in the macropores and the soil aggregates. This paper describes modification of the CRACK model, which includes an explicit description of the structure of an aggregated clay soil and can simulate the movement of water and solutes, to create CRACk-NP which incorporates nitrogen transformations and pesticide sorption and degradation. The application of the model to data from the Brimstone Farm experimental site in Oxfordshire, UK, is described. Results show that the model provides good simulations of both nitrate and pesticide leaching at the site but further testing is required to evaluate its performance over a wider range of hydrological conditions at this and other sites.