A nitrogen balance model for environmental accountability in cropping systems

In New Zealand and worldwide, growers are increasingly being required to demonstrate that their nutrient management does not have adverse effects on the environment. Since routine direct measurements of nitrogen (N) losses at an appropriate scale are currently unfeasible, a modelling tool that can be used to assess losses, both actual and potential, from farming systems is therefore needed. We present the upgraded N balance module for cropping systems (OVCrop) developed to be incorporated into the OVERSEER (R) Nutrient Budgets model. It presents an easy-to-use interface, requiring few but meaningful inputs, with the minimum flexibility needed to describe management of real farming systems. Following the developmental guidelines of OVERSEER (R) Nutrient Budget, OVCrop is designed to provide the long-term annual average of N leaching from any user-defined cropping rotation. OVCrop has been parameterized based on process-based model simulations for typical farm systems and environments of New Zealand. The intended use of the OVCrop is to help on-farm nutrient management and to demonstrate future compliance to N leaching regulations. OVCrop is a robust tool, simple enough to be used by people with a low to medium level of expertise, such as farmers and regional councils.