Whether you use a slurry tanker, irrigation pods or travelling irrigator, there are two critical elements when applying farm dairy effluent (FDE) – correct application depth and application area. To ensure maximum response, both must be considered.
Where storage is limited, farmers will usually need to apply effluent to the land in spring. If you are designing a new system, we strongly recommend including sufficient storage, to contain all the FDE produced over winter and spring. This will reduce the pressure on farm workers, and better utilize the nutrient value of the effluent.
Optimum application depth is determined by the soil infiltration rate, water holding capacity and soil moisture deficit. These are physical characteristics that all farmers should know about their soil. The rate of application must not exceed the infiltration rate; otherwise ponding and run-off will occur. Application depth should not exceed the moisture deficit, which is the water holding capacity less evapotranspiration.
Application area is important for managing the nutrient balance of your soil. Although the Regional Councils allow 150Kg N/Ha, this is likely to result in excessive potassium application. To ensure your FDE system is optimized for effluent volumes, we recommend you work with a consultant.
In general, the larger the application area the better; this can be achieved with a range of systems, including the following:
- Travelling irrigators offer 3mm minimum depth, although more typically 8-10mm. They require an extensive pipe reticulation system to increase application area.
- Fertigator and pod systems can be run intermittently to apply FDEat any desired application depth. An extensive reticulation system is required to increase the area of application.
- Slurry tankers have a range of spreading attachments and options. The splash plate on a Nevada tanker will apply 3-5mm in an even spray. Trailing shoes, dropper booms and injector units can also be installed on Nevada tankers to further reduce run-off. The obvious advantage of a slurry tanker is the ability to apply FDE to the entire farm without additional infrastructure.
Regardless of which system is used, it is most important that the application depth does not exceed the soil moisture deficit, and soil nutrient requirements are not exceeded. This will ensure maximum response from your free effluent fertilizer. To achieve this, irrigation should be delayed until late spring or summer, and applied to a large area.
