Dairy effluent is a natural fertiliser and soil conditioner and, if managed effectively, can enhance pasture growth and improve soil structure. Nutrients from effluent and sludge provide a valuable source of nutrients and organic carbon.
Increasing forage production
The application of dairy effluent and sludge to either pasture or crops is an effective way of increasing forage production. Several key principles need to be followed to effectively utilise and safely return effluent and sludge back onto the farm. These include:
- Allow sufficient land area to apply effluent at an agronomically sensible rate to meet the crop or pastures nutrient requirements.
- The main nutrients in effluent are not ‘balanced’ and each must be considered individually. Remember the nutrient that requires the largest reuse area sets the application rate. The nutrient concentration in effluent is dependent on a range of site-specific factors and is therefore variable from farm to farm. It is strongly recommended that farmers sample their own effluent or sludge and base their reuse activities on their own data.
- Total potassium per application should be no more than 60 kg potassium per hectare, and no more than 120 kg potassium per hectare per year. This applies for both liquid effluent and sludge.
- For liquid effluent, the total nitrogen application should be no more than 60-80 kg nitrogen per hectare. However, nitrogen application rates as sludge can be much higher due to the slow-release nature of much of the organic nitrogen in the sludge.
- Heavier applications increase the risk of problems such as nitrate poisoning, mineral imbalances and make less efficient use of the applied nitrogen as well as increasing the risk of losses to the environment.
- Treat effluent and sludge as a nutrient source rather than just a product for disposal.
- A lighter rate over a larger area is preferable to overloading a small area. If no chemical analysis is available, effluent should be spread at a rate of one megalitre per 12 hectares. This is based on typical nutrient concentrations found in surveys of farm treatment systems.
- Apply effluent or sludge to paddocks when there is no likelihood of runoff from the property.
- Rotate effluent applications around at least three or four different areas, if possible, to avoid excessive build-up of nutrients in the soil.
- Conduct regular soil testing of the areas where effluent is being applied to monitor nutrient levels and soil health.
- Isolate the paddock and restrict cattle grazing for at least 21 days after the application of effluent to pasture or crops. This withholding period will overcome any palatability or fouling issues, reduce the risk of any pathogens and allow the plants time to respond to the nutrients. For direct application of sludge to pasture, up to six to eight weeks may be required due to the solids content.