Auckland Council is investigating catchment-scale rehabilitation to address environmental degradation. Te Muri Regional Park, which is owned by the Auckland Council, is being used as a case study farm to better understand catchment-scale rehabilitation.

This report provides a baseline assessment of the effects of land use management and change on farm profitability and environmental performance. Farmax and OVERSEER® (Overseer) Nutrient budget models were used to gain an understanding of the Te Muri Regional Park performance, profitability and baseline nutrient losses. An area of 26ha is to be retired from grazing (conservation catchment) and further analysis was carried out in Farmax and Overseer to gain an understanding of the implications of retiring the conservation catchment on farm profitability and environmental performance.

The reduction in the farm effective area with the retiring of the conservation catchment resulted in economic farm surplus being reduced by approximately 25 per cent when the stocking rate is reduced to match the loss of pasture production. In terms of environmental performance the impact of retiring the conservation catchment resulted in a reduction of total farm phosphorus loss by 0.7 kg P/ha/yr. No change to the amount of nitrogen loss occurred when retiring the conservation catchment. The conservation catchment is fairly similar to the rest of the farm and therefore for a typical farmer considering retiring land for environmental benefit it would be difficult to consider retirement of a catchment so typical of the full farming enterprise. A more targeted retirement of unstable land would be a more favourable proposition for farmers, both economically and environmentally.

Auckland Council technical report, TR2015/003

February 2015