This project will develop a farm-scale sustainable nutrient management (SNM) decision support system (DSS) focusing on N and P management. There are two sub-projects: (1) theoretical development of the SNM-DSS; and (2) field-testing and evaluation of the SNM-DSS. A stand-alone computer version of the SNM-DSS will be available at the end of the project. The SNM-DSS will be developed from an exiting slurry management DSS (developed by the Agmet Group) with consideration being given to farm nutrient balance, timing of nutrient application and safe nutrient application. The DSS will have two driving principles: when there is no risk of storage capacity being exceeded, advice will focus on nutrient utilisations; alternatively, advice will focus on safe spreading and minimum pollution of ground or surface water, when slurry volumes are approaching full storage capacity. The SNM-DSS will be field tested at the farm-scale using four farms instrumented for soil water, weather and water nutrient transfers. The farmers will also keep diaries of activity and their expert view on spreading conditions. The DSS will be evaluated in terms of the reliability of forecast and the consequences of following advice.