Around 98 per cent of 4,500 dairy farms in the Waikato region discharge effluent to land under the permitted activity rule. The remainder are currently working under consents to discharge treated effluent to water.
Farm dairy effluent is a natural, dilute liquid fertiliser. It contains nitrogen (N), phosphorus (P), potassium (K), magnesium (Mg), sulphur (S) and trace elements that you’d normally pay for to have applied to pasture.
Think of dairy effluent as a resource, not waste. The average dairy herd (244 cows) produces the same amount of effluent as a town with about 3400 people, such as Otorohanga.
Table 1 below gives an indication of the potential nutrient supply within effluent, but each farm system is different so it's important to test effluent regularly.
|% dry matter||kg N/m3||kg P/m3||kg K/m3|
|Dairy shed effluent||0.8||0.45||0.06||0.35|
|Feed pad and dairy effluent sludge||4.0||1.35||0.3||1.05|
|Effluent from unstirred pond or effluent after separation||0.3||0.25||0.03||0.35|
|Solids from wintering barn||40||5.0||1.5||5.6|
Table 1 - Nutrient content of dairy effluent (kg/m3)
When spread over land and applied in timely fashion, the effluent of 100 cows can save farmers up to $2200 in fertiliser a year (based on 2010 fertliiser prices). This saving could be significantly higher for high input farms (for example, farms feeding supplements).
Applying the maximum amount of nitrogen from effluent allowed per year (150 kg per hectare for grazed grass), dairy shed effluent also provides the following approximate amounts of nutrients:
Effluent management systems in place on your farm should give you enough flexibility so that you don't irrigate:
Remember to cover water troughs when irrigating effluent.
Protect waterways on your farm by:
Soil acts as a living filter. It treats the applied effluent by changing it:
Soil can only filter so much effluent at a time. It’s important to match the irrigation depth to the capability of the soil. Land with impeded or artificial drainage, high or rising water tables or slopes of greater than 7 degrees have a higher risk from over-application, and therefore application depths should be adjusted accordingly to reflect soil and weather conditions. Note this could be less than the maximum application depth stated in Waikato Regional Council rules.
Too much effluent can:
Although effluent contains many nutrients which can impact on your farm management, it is the environmental effects of nitrogen that determine how much you can irrigate onto land. Too much nitrogen can reduce pasture performance and reduce water quality in neighbouring waterways.
If you know eactly how much nitrogen is in effluent, you can work out the most effective application rates for your land.
In the Waikato region, no more than 150 kilograms of nitrogen in effluent can be applied per hectare of grazed grass per year. You’ll need to get effluent tested to work out how much nitrogen is going onto your land during irrigation.
Most registered analytical laboratories offer this service for around $100. When used with a nutrient budget this is a small cost compared to the fertiliser savings that can be made over time when effluent applications are timed efficiently.
The Overseer nutrient budget can be used to help determine how much land is needed for effluent irrigation. For more information on Overseer, click here(external link).
Each effluent application must not be more than 25 millimetres deep. How deep you irrigate effluent over an area will depend on how much nitrogen you want to apply. Use our online calculation sheet to work out application depth, given that you know:
Once you’ve worked out the application depth, you’ll need to work out the application rate for your irrigator.
To ensure you don’t over-irrigate, use our online calculation sheet to work out effluent application rates for:
When irrigating check for effluent ponding, particularly in areas where there has been pugging damage. Stop ponding by avoiding irrigation in these areas, or improve the drainage by:
Because effluent contains a range of nutrients, irrigated areas will need less fertiliser. Talk to your fertiliser consultant about the reduced fertiliser needs of irrigated blocks.
In the Waikato region, applying effluent to land is a permitted activity. This means farmers can apply effluent without having to get a resource consent, as long as you follow these conditions:
If asked by Waikato Regional Council, the person applying the effluent must be able to show that they have met the above conditions.
Suggested guides and manuals(external link) for pond construction and effluent management are referenced in our For Farmers section.
Find out more about nutrient management.
For more information on our policy on discharges to land, check out section 3.5.5 of our Waikato Regional Plan.
Find out more about treating nutrient run off in wet areas.
Waikato Regional Council monitors stock density to find out where livestock farming is likely to have the most effect on soil and water quality in the region.
DairyNZ has recently released a new smart-phone app to help farmers apply effluent more efficiently. The Dairy Effluent Spreading Calculator app provides dairy farmers and effluent spreading contractors with guidance around nutrient application rates based on the depth and type of effluent they apply.
The app allows for nutrient application rates for dairy effluent to be easily calculated, based on a number of customisable inputs so effluent nutrients can be applied with greater precision. Click on this link to find out more about the Dairy NZ smartphone app(external link).