TAKING an average Waikato dairy unit and reducing its nutrient footprint is an initial goal for DairyNZ researchers working with staff and directors of Owl Farm.
The farm is one of 12 in the Partnership Farm Project, part of the industry’s effort to lower its nutrient and greenhouse gas footprint.
In 2014 the school farm’s directors recognised nutrient limitations were a looming regulatory reality they needed to deal with.
The 147ha property sits tucked between the main road to Hamilton and the Waikato River. Like all Waikato farms it will be subject to nutrient limits under the Healthy Rivers plan.
“What we found was that we achieved the nutrient reductions, not through a revolution, but more of an evolution with changes around lots of little things.
“The main changes we made were to reduce bought-in feed from 20% to 11%, put 8% of the farm into turnips and reduce the stocking rate from 2.95 cows a hectare to 2.8,” DairyNZ’s Owl Farm manager Louise Cook said.
Nitrogen fertiliser use was cut by 13kg a hectare and winter application was avoided.
The reduced nutrient loss box they wanted to achieve was ticked.
Nitrogen losses to waterways dropped by 14% to about 36kg N/ha.
“But then, 18 months ago, we learnt greenhouse gases would have to soon be included in reductions.”
Working back over farm data the researchers found their achievements in reducing nutrient losses had also helped cut the farm’s gas footprint.
The cuts to nitrogen inputs and lowered total feed inputs also sliced 8% of the farm’s gas emissions, by about a tonne a hectare from 13.6t/ha to 12.5t/ha.
Meantime farm operating profit per hectare has lifted by 14%.
The greatest slice came off gases through reducing the farm’s nitrogen surplus.
Nitrogen surplus is the net difference between fertiliser nitrogen plus nitrogen in imported feed less nitrogen output in milk.
DairyNZ data from 400 Waikato farms shows with every 100kg surplus eliminated from a farm system, 4.26t/ha of gases were eliminated with it.
Owl Farm’s reduction in its nitrogen surplus of 20kg a hectare therefore sliced off 0.85t a hectare of gas with it.
Secondly, reducing the amount of bought-in feed and growing more on the farm contributed alongside the nitrogen reduction to total gas reductions.
Owl Farm’s change to more farm-grown feed achieved a reduction of almost 0.3t of gas/ha, based on DairyNZ data from 400 Waikato farms.
Growing more feed on-farm eliminated carbon emissions generated by transporting bought-in crops like palm kernel.
But Cook cautioned as the system becomes more and more efficient it is harder to achieve even greater gas reductions.
However, given many farms are around Owl Farm’s average category, there is plenty of room for the industry to make some significant early improvements in gas losses.
Cook said while aiming to reduce gases will typically also reduce nitrogen losses it does not always apply the other way, in that nitrogen reductions might not always also lower gas losses.
That can be because of changes in things like farm infrastructure, which may contain nitrogen-rich effluent but result in greater losses to the atmosphere.
Owl Farm researchers have two options they could pursue for further reductions.
One involves reducing stocking rate by a further 7%.
The other involves building a feed-pad to capture nutrient losses, increasing the stocking rate and adding maize silage to the system.
DairyNZ farms systems specialist Chris Glassey urged farmers wanting to achieve Owl Farm’s 1t gas/ha reduction to keep good records on nitrogen applied and feed used.
That will help calculate their farms’ nitrogen surpluses, from which they can make management changes that will also reduce gases.
