There is no ''one-size-fits-all'' solution to farming within nutrient limits, DairyNZ economist Sam Howard says.
Leading a workshop at the South Island Dairy Event (Side) at Lincoln University on June 24, Mr Howard said we did not yet know what the limits would be, but it was important for farmers to know what they were leaching now, so they could figure out how to alter it, if necessary.
Depending on their location, problems could be nitrogen, phosphorous or faecal matter.
Factors affecting leaching included stocking rate, the fertiliser needed and when and how it was applied, soil type and drainage, winter grazing, rainfall total and timing, supplements and bought-in feed, pasture eaten, and crop rotation.
Options for reducing leaching, put forward by workshop participants, were converting from border dyke to pivot irrigation, improving irrigation efficiency, lowering stocking rate, applying less fertiliser or at different times, trying alternative fertilisers, increasing the area over which effluent was spread, increasing effluent storage capacity, substituting some spending on nitrogen for supplementary feed, growing more clover to provide more nitrogen, trying pasture diversification and adding more humus to the soil to improve its moisture-holding capacity.
''There are many ways to reduce nitrogen leaching. All have different impacts on the profitability of your business,'' Mr Howard said.
''Look at models with your farm consultant. See what changes could mean for you.
''It's very much driven by understanding leaching. See what's in your control and what's outside it.''
Those on free-draining soils were ''stuck with it'' and had to learn to work with it, Mr Howard said. Farmers could share ideas with neighbours who had similar soils.
DairyNZ principal scientist David Chapman had also been studying how farming systems affected nutrient leaching. At his Side workshop, he said nitrogen efficiency could be improved by reduced fertiliser use; increasing production per cow, so more nitrogen left the farm in milk; increasing cow longevity and fertility; reducing the stocking rate; using low-nitrogen supplements; and standing stock off pasture during high-risk times of the year - ''anything that results in less urine patches''.
Only about a quarter of the nitrogen cows ingested went into milk, while about two-thirds was excreted in urine and therefore leachable.
A Canterbury study using two farmlets showed a lower stocking rate could be very profitable while using and producing less nitrogen. It depended on high per-cow production from home-grown feed, Dr Chapman said. Good cow genetics, pasture quality and intake were the key to productivity. High management skills were also required.
The dairy industry needed to extend its thinking from the dairy platform alone to the full land resources it used, he said.
Wintering land, transitioning stock from grass to silage and grain production should be factored in. Farmers should talk to their graziers when considering their nitrogen footprint.