The effluent system is required to be modelled when effluent is captured from a structure (Milking shed, feed pad, wintering pad/shelter, standoff pad). The structure defines how/what effluent is collected and therefore affects what effluent needs to be managed by the system (liquid, solids and/or pond solids).
The dairy effluent system is used to process effluent from the milking shed. Other structures may define their own effluent management or utilise the dairy system.
Storage affects nutrient losses. The longer effluent is stored, the more nitrogen is lost to the atmosphere as volatilisation and denitrification and the more nitrogen settles as solid. The application rate and timing of application has an effect on nutrients taken up by plants and in the soil.
The management systems describe the storage of effluent on farm, the following options can be selected in OverseerFM:
- Spray from sump - there is no separation of effluent into solids and liquids. There is little volatilisation loss on spraying and effluent is applied on the day it is generated, i.e. there is no ability to change the time effluent is applied as there is limited storage.
- 2 pond + discharge – 2-pond treatment system is used and liquid effluent is discharged directly to a stream. Liquid effluent is not applied on farm. You are required to describe what happens with the pond solids – spread on blocks or other (exported).
- Holding Pond – there is a facility to store effluent on farm and you have options on when you can apply liquid effluent. You are required to describe what happens with the pond solids.
- Holding Pond – Solids are separated - there is a facility to store effluent on farm and you have options on when you can apply liquid effluent, solids are separated before they enter the holding pond. When this management option is selected you are then required to enter what happens with pond solids and solids management (solids that are separated before entering the pond).
- Exported – All effluent is exported off farm, there is no ability to store effluent.
When there is a facility to store effluent on farm liquid effluent management needs to be described. The following options can be selected in OverseerFM:
- Spray regularly - some separation occurs with some loss to the atmosphere. There is flexibility to modify the time of effluent applications therefore the farmer can avoid applications during wet days or in wet weeks. Typically, this affords about 1-2 weeks storage capacity.
- Stir & spray regularly – This is the same as above except there is no separation as the liquid effluent is being stirred.
- Spray infrequently - there is more settling of solids (hence higher nutrient contents in sludge), and more ability to alter the time of effluent applications but effluent is still applied within the month it is generated.
- Exported – Liquid effluent is exported from on farm storage.
When liquid effluent is applied on farm, you are required to allocate the application to a block and select the application rate. The following options can be selected in OverseerFM:
- Low application method – low rate type system (systems capable of applying rates of 1-10mm)
- <12mm – Metered pivot application systems
- 12-24mm – Travelling irrigators
- >24mm – Stationary irrigators, canons or contractors pumping
Ponds solids are either spread on blocks or other (exported).
Excellent guidance on the definition and management of effluent systems can be found in the DairyNZ Publication "A farmer’s guide to managing farm dairy effluent - A good practice guide for land application systems" which can be found here