Applying effluent to land

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.

Fertiliser value of effluent

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
Separated solids	20	4.5	0.72	2.1
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:

20 kg of phosphate per hectare.
117 kg of potassium per hectare.
Approximately 20-30 kg of sulphur per hectare.
Smaller amounts of magnesium and calcium.

Applying effluent

Effluent management systems in place on your farm should give you enough flexibility so that you don't irrigate:

when soil is waterlogged (too wet to absorb the effluent)
if there is an equipment breakdown.

Remember to cover water troughs when irrigating effluent.

Protect waterways on your farm by:

not irrigating within 50 metres of a water supply
leaving a strip of non-irrigated land next to all watercourses – at least 20 metres wide
ensuring that spray drift isn’t getting into nearby streams or rivers.

Soil – a living filter

Image of a soil profile showing the zone of effluent wetting.

Soil acts as a living filter. It treats the applied effluent by changing it:

physically – filtering out effluent particles, breaking them down and incorporating them into the soil structure
chemically – absorbing nutrients and making them available to plants
biologically – harmful micro-organisms (such as bacteria) present in the effluent are retained by the soil, or are killed when the effluent dries or when they become exposed to sunlight.

Don’t apply too much

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:

kill pasture – especially where effluent has ‘ponded’ on the soil surface
pollute nearby streams and rivers – where it runs off paddocks into waterways
pollute ground water – by seeping too deep into the soil
be an ineffective use of nutrients - by seeping past the root zone before the plant can utilise it.

Working out how much effluent to irrigate

Image of a man scratching his head.

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.

How deep does each application have to be?

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:

the nitrogen content of the effluent
how much nitrogen (kilograms) you want to spread per hectare.

Working out application rates

Once you’ve worked out the application depth, you’ll need to work out the application rate for your irrigator.

Spray irrigators

Using the same principal as a rain gauge, mark a scale on the sides of several containers.
Place the containers within the area being irrigated.
Stop irrigating when the desired depth (maximum of 25 mm) has been applied.

Other irrigators

To ensure you don’t over-irrigate, use our online calculation sheet to work out effluent application rates for:

travelling irrigators – the distance an irrigator needs to travel (in metres) per hour
stationary spray ‘cannons’ – the length of time a spray head can stay in one place
tanker systems - the distance an irrigator needs to travel (in metres) per hour.

Ongoing irrigation management

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:

loosening the soil in small ponding areas with a spade
breaking up the soil surface – for example, by shallow ripping.

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.

Regulations for applying effluent

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:

No more than 150 kilograms of nitrogen can be applied per hectare, per year (1.5 applications at 25 mm deep and 0.04 percent nitrogen).
The farmer/contractor must have contingency measures in place in case there is prolonged wet weather or a pump breaks down.
Any ponds or effluent holding facilities must be sealed to reduce leakage.
The farmer/contractor must spread effluent and sludge in a way that reduces odour and spray drift.
Each effluent application must not be more than 25 mm deep.
Effluent must not run off the land into waterways.
Effluent must not pond on the land surface after application.

If asked by Waikato Regional Council, the person applying the effluent must be able to show that they have met the above conditions.