Even regrassing can have implications when it comes to complying with nutrient limits.
Canterbury farmer Leo Donkers and his team in Camden Group, a family-owned dairy farming operation that includes three farms with an 800ha total milking platform area, have embarked on a large-scale regrassing programme that will renew the entire area in three years.
The programme aims to grow more grass of better quality and reduce the level of imported feed, but importantly it also needs to ensure the farms stay within their nitrogen baseline limit under Canterbury’s land and water regional plan.
The nitrogen baseline is the average annual nitrogen loss from 2009 to 2013, determined by the Overseer model.
To prepare for having paddocks out during the regrassing programme extra supplement was bought in but the stocking rate was lowered from 3.5 to 3.4 cows/ha, helping to limit any extra nitrogen leaching.
As last season progressed the additional growth from paddocks regrassed in spring meant much of the supplement wasn’t needed and in fact silage was cut from six paddocks.
In 2012-13, before the regrassing programme, Willsden Farm, one of the Camden group farms, used 878kg drymatter (DM) a cow of silage. In 2013-14 that was almost halved with silage fed dropping to 478kg DM/cow.
Ravensdown agri-manager and certified nutrient management advisor Sonya Perkin told an Agriseeds and DairyNZ field day at Willsden that reducing supplement imports was key to remaining within nitrogen limits when regrassing.
“If your goal is to increase stocking rate by regrassing then you will increase your nitrate leaching,” she said.
In Camden’s case nitrogen leaching for this season, based on Overseer, has dropped below the baseline average despite the stocking rate being returned to 3.5 cows/ha because imported feed has been slashed.
Converting the extra feed to milk is also a big part of ensuring nitrogen leaching isn’t boosted.
‘If your goal is to increase stocking rate by regrassing then you will increase your nitrate leaching.’
The Overseer model gives a loss figure based on what’s coming in to the system in terms of nutrients and what leaves the property as feed or animal products such as milk.
Even though they’re only part-way through the grand regrassing programme, Camden’s experience has been that, providing good grazing management practice is used, the milk production rewards follow.
This season Willsden is targeting 486,000kg milksolids (MS), up from 458,388kg MS in 2011-12.
Improved palatability of new grasses, particularly the short-term Italians and the perennial tetraploids, is credited with improved pasture utilisation with cows readily hitting residual DM targets so they’re eating more.
An estimated lift in metabolisable energy of about one megajoule has helped boost production already.
Cultivation has been done by direct drill, reducing nitrogen loss through the regrassing programme, although the Overseer model assumes some additional loss because there’s little to no plant uptake of nitrogen once old pastures are dead until new plants are establishing.
