Nutrient Management

Wednesday, 22 January 2020 at 3:46pm

The National Policy Statement for Freshwater Management, issued by Central Government in 2011, requires all regional councils to set quality limits on all ground and surface water bodies within their region by December 2030.

Under the Sustainable Dairying: Water Accord, milk companies have signed up to collect and model nitrogen (N) loss and nitrogen conversion efficiency (NCE) from all dairy farms. This means farmers will need to provide N loss and NCE performance information and benchmarks to their suppliers.  Here is some advice from the team at DairyNZ:

Winter crops

Pathway to water: Leaching due to stock urine in a concentrated spot; minerals stirred up during tillage; poor fertiliser application or winter fallow leaching.

Practices to reduce N leaching:

• Urine N leaching can be reduced through appropriate paddock selection, grazing time and grazing regime.
• Fertiliser N leaching can be reduced through the use of crop calculators to gauge need and precision application to ensure appropriate application and timing.
• Winter fallow N leaching can be reduced through the use of a cover crop or late harvests.
• Mineral N leaching can be reduced through the use of minimal tillage.

Fertiliser application

Pathway to water: Leaching if fertiliser is applied in inappropriate amounts, times or locations

Practices to reduce N leaching:

• Avoid direct leaching by not applying in winter or to water logged soils.
• Soil test to ensure other nutrients are not limiting.
• Optimise your response rate and pasture utilisation.

Effluent irrigation

Pathway to water: direct runoff or leaching due to application at inappropriate amounts, times and locations.

Practices to reduce N leaching:

• Measure effluent application rates to ensure they are suitable for your soil type
• Ensure storage is sufficient so you don’t have to irrigate during wet periods and busy times
• Have an effluent block that is a suitable size for your application and makes efficient use of your nutrients.

Effluent ponds and related infrastructure

Pathway to water: Runoff due to poorly maintained infrastructure, leaching due to unsealed storage

Practices to reduce N leaching:

• Ensure storage ponds and tanks are lined to prevent leaching and big enough to avoid irrigation onto wet soils and during busy times
• Maintain your infrastructure regularly to avoid leakage, burst pipes, blocked nozzles and pump failure.

Irrigation water

Generally irrigation water is not a source of nutrient loss. Like rain, irrigation water decreases the available water holding capacity of soil which increases the risk of N leaching. Oversaturation of soils can also lead to pooling and runoff.

Grazing cows and urine patches

Pathway to water: Most N leached in dairy systems comes from urine patches. The rate of N applied per ha in a urine patch can be equivalent to 500-1000 kg N/ha /yr. Plants cannot use all the N before it drains down the soil profile and leaches.

Practices to reduce N leaching:

• Use off-paddock facilities strategically to capture the N from dung and urine - for more information on stand-off facilities click here.
• Grazing cows off-paddock in the autumn months before winter rains flush N downwards reduces N leaching the most.

Grazing cows on your farm during winter

Pathway to water: Most N leached in dairy systems comes from urine patches. The rate of N applied per ha in a urine spot can be equivalent to 500-1000 kg N/ha /yr. Plants cannot use all the N before it drains down the soil profile and leaches. Grazing cows off in winter will reduce the N leached on the milking platform and can have positive effects on soils and pasture grown.

Practices to reduce N leaching

• Grazing cows off farm in winter may help reduce N leached on your milking platform, but just transfer the leaching to another area. Wintering off farm also has large system effects which you need to review carefully.

Before you make changes to the farm system or invest in off-paddock facilities, analyse your situation thoroughly to ensure it solves your problem, and your system remains profitable.

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