If managed carefully, irrigation of dairy effluent to pastures and crops can make good use of the nutrients, organic matter and water.
Dairy effluent contains many nutrients and can be used on a range of pasture and crops, which has economic benefits.
Applying dairy effluent to pastures can increase pasture growth considerably, according to a number of Australian and overseas studies.
Victorian research has shown large and valuable responses can be obtained for both pasture and forage crops.
The response varies depending on the time of year and is due to both the nutrient and water content of the dairy effluent.
When applying liquid and solid dairy effluent, appropriate buffer distances from surface waters should be maintained to avoid contamination.
Effluent should be applied to pastures or crops at the right time and in amounts that the plants can use the water and nutrients.
If too much is applied at one time or if applications are repeated too often in the one place, there is a high risk of runoff to streams or groundwater.
Dairy effluent is a valuable source of nutrients. Levels of nutrients contained in dairy effluent are generally lower than that of fresh manure, due to many factors.
Nitrogen availability to plants is generally less with effluent than with artificial fertilisers because some of the nutrients are bound up in the organic matter.
In liquid effluent, a high proportion of nitrogen will be in plant-available forms.
Sludge often has a high proportion of nitrogen in organic (slow release) forms. Some of this nitrogen will be made available for plant use into the future.
Potassium has high availability and is a potential problem since it can replace magnesium in pastures making them more prone to cause grass tetany in cattle.
This is only likely to be a problem if effluent is applied in the tetany season or restricted to a small part of the farm.
Nutrient content of stored effluent is less than directly applied effluent.
Some nitrogen is lost to the atmosphere whereas phosphorus and potassium and some of the nitrogen settle out in the sludge.
The nutrient content of effluent varies widely and is dependent on many factors. The most accurate method of determining the nutrient value of your effluent is to take a representative sample and have it tested.
This will then allow you to calculate appropriate application rates.
The main aims in applying effluent to your pastures or crops are to maximise the use of nutrients by the plants without causing nutrient overload or waterlogging and minimise the loss of nutrients by runoff to streams and drains or leaching through the soil to groundwater.
Avoid applying effluent to the same area year after year.
This can lead to overloading the soil with some nutrients such as potassium.
Care also needs to be taken with salts which may be contained in the effluent.
So, unless you test your effluent and monitor the soil where it is applied on a regular basis, it is recommended that you rotate your applications around at least three or four areas, moving each year.
Applying effluent to lower fertility paddocks will increase the fertility in these areas.
Normal fertiliser applications needed to be altered in paddocks were effluent has recently been applied.
Effluent from your storage pond (second of two ponds or your single pond) should be applied over summer and autumn, so the pond starts each wet season almost empty.
Applying effluent during the wetter months runs the risk of runoff to streams or leaching to groundwater when soils are saturated.
Aim to empty the pond before soils become saturated.
Apply effluent when pasture or crops are actively growing, so that they can use the nutrients.
Applying to recently grazed pasture will allow the withholding period to be incorporated into the grazing rotation.
Contact your vet if you have concerns about any specific animal health problems associated with applying dairy shed effluent to pastures or crops.
- Agriculture Victoria