Reducing total N fertiliser applied annually
- Reducing annual N fertiliser use per ha potentially reduces a farm’s N surplus and therefore N leaching. Annual pasture production per ha will also be reduced
- Research results show a diminishing DM response to N fertiliser at annual rates above 200kg N/ha. The research also demonstrated that annual rates above 200kg N/ha could not be justified economically due to the high cost associated with harvesting the extra grass grown
- At annual rates of less than 200kg N/ha research shows that MS production will drop by approximately 1kg for every kg of N fertiliser not applied
- To manage reductions in N fertiliser where less than 200kg N/ha is used requires appropriate farm system changes to ensure profit is maintained
- Reduced N leaching will be greater on farms where applied N use is high relative to milksolids production (i.e. less than 6kg of MS/kg N)
- There is a wide range in efficiency of N fertiliser use on dairy farms, as indicated by the ratio kg MS produced per kg N applied.
Getting the best response to N fertiliser
- Avoid direct leaching associated with applying in winter and to waterlogged soils
- Optimise response rates and pasture utilisation
- Ensure other nutrients are not limiting
- N is a cost effective way of increasing feed supply.
Grazing cows off in winter
- Grazing cows off the farm during winter will reduce the N leached on the milking platform and can have positive physical effects on soils and pasture grown
- Wintering-off will mean there is more feed on farm at the planned start of calving (PSC) unless the calving and/or drying off dates change, or changes are made to the amount of supplements or N used
- If pasture covers are higher at the PSC then it will be possible to feed cows better through the early stages of lactation and/or reduce supplement use
- Grazing-off during winter should be evaluated by comparing the milk price and extra production versus grazing costs.
Using off paddock facilities
- Off paddock facilities, such as feed pads and stand-off pads, can be used to reduce N loss by intercepting the N from dung and urine
- The mitigation opportunity is greatest over autumn, where N deposited will be at risk of leaching over the coming winter months
- Restricting grazing to 8 hours a day over the autumn/winter period, without supplementary feeding, has been shown to have no impact on production, but has the potential to reduce N leaching by 15-20%
- Use of off pasture facilities may cause animal health and welfare issues, in particular where existing structures were not designed to hold cows for extended periods. If off pasture facilities result in intensification (i.e. more feed is used), then more N may be introduced into the system and undo the environmental benefit
- Off pasture facility construction is a capital intensive process and appropriate long term budgeting techniques are required to ensure that the cost benefit ratio is positive.
Winter crop management
- Mineral N leaching can be reduced by minimal or no tillage establishment methods
- Urine N leaching can be reduced through paddock selection, forage crop selection, grazing timing and regime
- Timing and placement of fertiliser applications can affect leaching. The use of crop calculators and precision application can ensure appropriate timing and application
- Winter fallow leaching can be reduced though the use of a cover crop or cultivating as late as possible.
Managing effluent systems
- Application rates (depth of applied effluent) should be low enough to prevent losses of nutrients below the root zone
- Storage ponds/tanks should be of sufficient size to prevent the necessity of irrigating onto wet soils and to allow for easier management of farm dairy effluent (FDE) systems during busy times of the year. Storage ponds/tanks must be sealed (i.e. not leak)
- Efficient water use and rainwater diversions can significantly reduce the FDE storage requirement
- Effluent blocks should be sized correctly to ensure efficient use of nutrients.
Culling cows early in autumn
- This will remove some urinary N from pasture during a risk period
- It will also reduce feed demand
- This may allow a reduction in fertiliser application or imported feed
- Before introducing you need to compare the lost milk production and revenue against saved costs
Calculating Comparative Stocking Rate
- Comparative stocking rate (CSR) calculated as the kilogram liveweight per tonne of dry matter (kg Lwt/t DM) offered, is a method of assessing the balance between feed demand and supply on farm
- Getting CSR as close to optimum as possible increases feed conversion efficiency and helps reduce N surplus
- Getting as close as possible to the optimum of 75-80 will help improve profitability.
For further information see the Reducing Nitrogen Loss guide.