The model assumes that productivity is in quasi-equilibrium with inputs and management practices described. If a slow solubility material is used, the increase or decrease in yield that results from the use of that product is reflected in animal intake, which is determined from animal numbers, the class of animal, and their productivity.
The model differentiates between rock phosphate and other sources of P when calculating the P runoff risk. The slow release of N from organic materials (effluents, composts) is included in the model, but not slow release of N fertilisers.