Exploring potential dairy and arable farm system integration to enhance nutrient circularity: A case study analysis from Oamaru's coastal plains

The evolving challenges facing New Zealand's agricultural sector, particularly in dairy and arable farming, include rising costs, regulations, and environmental sustainability goals. In response, this study evaluated the potential benefits of enhancing nutrient circularity in a collective dairy and arable farming system aimed to reduce synthetic fertiliser use, lower greenhouse gas (GHG) emissions, and decrease nitrogen (N) leaching. Using an “Innovation System Approach” that included Farmax Dairy and OverseerFM, a North Otago dairy and arable farm system was modelled to compare current practices with two scenarios aimed at optimising manure use for arable production. Scenario 1 introduced an off-paddock facility for restricted autumn grazing and wintering cows, with collected manure applied to arable crops. Scenario 2 included a pasture phase in the arable farm's crop rotation for dairy grazing and fertilised arable crops with effluents on the dairy platform. Both scenarios significantly reduced synthetic fertiliser inputs through their partial substitution with manure. N leaching decreased by 8-17% due to reduced N fertiliser use and excreta returns to the dairy platform. On-farm GHG emissions were effectively unchanged (1% decrease) due to pollution swapping. These results highlight the potential benefits of circular farming practices in NZ’s dairy and arable farming systems, improving resource-use efficiency and mitigating environmental impacts through optimised nutrient supply and manure management.