Using a paper prepared with Miranda Hunter, of Roslin Consultancy Southland, Ina Pinxterhuis, of DairyNZ, and Jo Kerslake, of AbacusBio, she told a South Island Dairy Event (SIDE) workshop farmers needed to understand their nutrient budgets and find out how changes would affect them before they made them.
“Poor understanding and over-simplification can put both the achievement of reduced nutrient loss and the financial viability of the dairy farm business at risk,” Dalley said.
“The options available to individual farmers need to be assessed against overall farm performance and efficiency, and tailored to meet the goals of continued business viability and improved water quality for their particular farm and region.”
She said changes to stocking rates would impact on nitrogen losses by different amounts depending on soil types, but stocking rates were also affected by days in milk, wintering on or off and rearing fewer or more replacements on farm.
“Adopting farm management practices that improves reproductive performance is one strategy that could be used to manage nitrogen loss. If you need to rear less replacements because there are fewer empty cows then your farm’s stocking rate will be less.”
Dalley said nitrogen losses mainly occurred from animal urine patches and wintering cows on crops with a high nitrogen content had a high risk of nitrogen loss due to stocking densities in the crop paddock.
As well, more rainfall was likely to fall during winter washing the urine into waterways especially as there was no plant uptake until the paddock was re-sown in the late spring.
“Removing winter crop grazing from a dairy system can significantly decrease nitrogen loss but, in practice, achieving this will depend on off-farm grazing being available or significant capital investment in infrastructure for an off-paddock wintering system.
“However, sending your cows to another farm for winter grazing does not solve the problem, it simple shifts it to another area.”
She said building feedpads and wintering barns was not a quick-fix solution.
“In a study in the Horizons catchment the incorporation of a free-stall barn reduced nitrogen leaching by 34%. However, a 17% increase in cow numbers and a 71% increase in milksolids production were required to cover the cost of the winter facility. Under the intensified scenario the nitrogen leaching returned to the level predicted prior to the capital investment in the barn and so resulted in no environmental benefit.”
She said off-paddock wintering systems must be accompanied by a robust nutrient management plan to ensure the nutrients imported as feed were used as efficiently as possible and solid fertiliser applications were reduced or tailored to meet requirements and the risk of nutrient build-up in soils minimised.
“Whatever you choose to do, do your homework first and don’t rush any decision. There will seldom be one thing that you can change to meet the new targets.”
