Summary of Best Management Practices
Dr Richard Eckard
Data from a completed project funded by DPI and the Dairy Research & Development Corporation
The following Best Management Practices were developed to both minimise the environmental impact of, while optimising the economic response to N fertiliser, in the temperate regions of SE Australia:
General guidelines for N management
a. Before each N application calculate the likely N response for the target pasture (i.e from lookup tables or DSS) and compare the cost of the pasture produced to other purchased feed options.
b. High stocking rates and stocking intensity will result in high losses of N from urinary deposition. High densities of stock in small areas (i.e. sacrifice blocks, calving pads) will result in point source losses of N.
c. Only apply N when pasture is actively growing and can utilise the N.
d. Avoid applying N fertiliser near streams/riparian zones and over drainage lines within a paddock.
e. Do not apply above 50 kg N/ha in any single application and do not apply N closer than 21 (30 kg N/ha in spring) to 28 (50 kg N/ha) days apart, as this will increase N losses exponentially.
f. Applying less than 30 kg N/ha in any single application will often produce unpredictable N responses i.e. 20 kg N on 2 hectares may produce less than 40 kg N on 1 hectare. However, likewise (from point e.) 80 kg N/ha on 1 hectare is likely to produce less than 40 kg N on 2 hectares.
g. Where annual N application rates exceed 250 kg N/ha per year, a proactive strategy of soil testing and liming may be required to prevent soil acidification. Usually 2.5 tonnes of lime per hectare will be required every 2 to 3 years.
a. Ammonia volatilisation from dairy farming is not considered an environmental issue in Australia at this stage.
b. Between May and November ammonia volatilisation losses from urea fertiliser are to small to be of economic or environmental concern, and certainly do not justify switching to higher-cost N fertiliser sources.
c. If urea fertiliser is applied in the summer months, consider applying the N fertiliser 2 to 3 days prior to each grazing. This minimises wind speed at ground level thus reducing ammonia removal, while absorbing some of the ammonia directly into the plant canopy.
d. Ammonia volatilisation losses in summer average around 14%, which still does not economically justify switching to other more expensive sources of N.
e. In summer, where soils are dry and evaporation is high, avoid applying urea fertiliser after a rainfall event, as this may increase volatilisation losses above 20%.
Nitrate leaching and denitrification
a. Avoid N high rates on waterlogged soils, particularly if soil temperatures are above 10 °C, as this will increase denitrification rate.
b. While soils are near field capacity (mid-July to September), or on free draining soils (sands/kraznozems), avoid applying N fertiliser before heavy rainfall and for at least 2 to 5 days after heavy rains depending on how readily the soils drain. If N must be applied, then apply lighter rates of N and use urea rather than a nitrate containing N fertiliser.
c. Avoid heavy stocking intensity (i.e. sacrifice blocks) on a single paddock during high rainfall periods, as this will result in significant urinary deposition in a small area, with pugged soils resulting in either increased denitrification or surface run-off loss of N.
N fertiliser sources
a. Urea is currently the cheapest straight source of N. Ammonia losses from urea fertiliser are not large enough to justify using other N sources.
b. Di-Ammonium Phosphate (DAP) does not volatilise readily under most conditions in SE Australia and is potentially the cheapest source of N available, if the P is needed at the same time.
c. When using DAP, calculate the N rate applied and consider ‘topping up’ with urea to ensure an adequate N fertiliser rate i.e. 2 bags of DAP/ha will only apply 18 kg N/ha; this should be topped up with urea to at least 30 kg N/ha to ensure a predictable N response.
d. When applying N and P fertiliser together, defer to the best management practices as applicable for minimising overland flow losses of P.
e. Ammonium sulphate can be a useful source of both N and replacing soil S, particularly where DAP has replaced routine superphosphate use. However, ammonium sulphate is an expensive form of N and it will acidify the soil rapidly with regular use.
Dung and urine management
a. Minimise the time that cows spend in the laneways.
b. Ensure that laneways drain back to paddocks and not to drainage lines and waterways.
c. Effluent should be viewed as a valuable fertiliser resource, and nutrient testing should be used to ensure that no more than 50 kg N is applied to a pasture at a time.
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Last modified:30 October, 2007
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