On-Farm Management Practices on Nutrient Pollution Control and an Impact Assessment on Water Quality

The impacts of land use on the environment is becoming increasingly important to New Zealanders, and is being reflected in government policies around the environment and water quality. The Tokomairiro River catchment has had ongoing water quality issues, as a result of farming in the area. Previous studies have been undertaken, however water quality modelling has not been undertaken for the catchment. The aim of this research was to model the effects of on-farm management practices on nutrient export over time in the Tokomairiro catchment, and assess the impact on water quality. It was aimed to model the effects both on an existing scenario as well as future scenarios with land use changes and climate change. The research collected data from the local government and endeavoured to capture additional existing information from a questionnaire. This data was then input into the modelling scenarios. Modelling outputs showed that nutrient export worsened in all future scenarios. Nutrient concentrations in the climate change scenario decreased as a result of increased flow, but nutrient loads and yields increased, indicating an increase in export. The research identified that in all scenarios, nitrification inhibitors had the greatest reduction in total nitrogen concentration, and the management of stock crossings had the greatest impact on total phosphorus concentrations. Despite the outputs, nitrification inhibitors are not recommended due to the on-going research regarding residue in milk products. The questionnaire highlighted that both farms used fertiliser however neither used nutrient budgeting. Although not modelled, the merits of using nutrient budgeting were identified in the literature in regard to reducing nutrient leaching. Several limitations existed in the project, which influenced the results and conclusions. There are a number of opportunities to further the research from this project, particularly regarding further data collection, model refinement and modelling of a broader range of scenario and on-farm management practices