Sustainable utilisation of dairy shed effluent

Author:   O’Keefe M.F.

Contact:   okeefe.michael@saugov.sa.gov.au

Keywords:   Effluent recycling, freshwater conservation, nutrient budgeting, effluent irrigation, mechanical separation and gravity settling

Abstract:
“Resource – not Waste” the new dairy shed effluent paradigm is a program funded by the National Landcare Program that aims to provide practical assistance to dairy farmers, enabling them to implement best management practice for dairy shed effluent, taking them beyond mere compliance with the current state legislation.

Rural Solutions SA (RSSA) senior consultant Trevor Clark updated dairy shed effluent guidelines for the South East, Mt Lofty Ranges, South Australian Murray Darling Basin, and Northern and Yorke regions of South Australia.  The guidelines were released to farmers between 2005 and 2007 and RSSA consultant Michael O’Keefe has been providing technical assistance on dairy shed effluent management to South Australian dairy farmers over the last two years. 

RSSA has been involved in the design of dairy shed effluent management systems for dairies ranging between 200 cows and 2,000 cows.  RSSA has provided advice and design services to existing dairies, as well as completing preliminary feasibility planning and designs for new dairies. This process has been conducted in accordance with best management practice (BMP) for dairy shed effluent management.  The key elements of BMP are: effective separation of the solid and liquid components of effluent, reducing freshwater consumption for dairy yard washing, recycling effluent and utilizing effluent to replace synthetic fertilizers (i.e. regarding effluent as a resource, not a waste product).

The program aims to improve effluent management by dairy farmers through highlighting examples from demonstration farms, as well as disseminating up-to-date effluent management technology via on-farm technical assistance.  After the core elements of BMP have been implemented there are several other benefits that farms can achieve with their dairy shed effluent management system.  Larger dairies are adopting more advanced effluent treatment systems.  Many are installing mechanical separators and multi-stage gravity settling ponds to separate the solid and liquid components.  This process generates two valuable, and re-usable products.  The separated liquid effluent can be recycled for yard washing and/or used as fertigation when pumped through centre pivot and traveling irrigators.  The separated solids can be used as a soil ameliorant, composting feedstock or dried and re-used as a bedding source in free stall barns.  Dairies that utilize floodwash tanks for yard washing can use up to 90,000 litres of freshwater per day.  If this volume is replaced by recycled effluent the dairy can reduce its annual freshwater consumption by 36 megalitres, whilst significantly reducing the volume of effluent that requires managing.

Historically the design of dairy shed effluent systems has been about how effluent can be captured and stored. Frequently designs have resulted in the need to spread stored effluent during the winter, when plant uptake is poor or when soils are waterlogged.  Applying effluent at this time of the year greatly increases the risk of contaminated run-off being generated. Dairy shed effluent contains valuable nutrients, but if spread on paddocks at the wrong time of year these nutrients can enter water resources and become potent pollutants.

The new approach to designing dairy shed effluent storage and management systems is to firstly address the question of how the effluent is going to be spread.  Once the spreading method has been decided, the effluent can be treated and managed to best suit the spreading method and optimize nutrient utilization.

Trevor Clark designed a spreadsheet model to assist in spreading dairy shed effluent. The model determines a sustainable effluent spreading rate based on several input parameters such as feed, fertiliser and effluent, and calculates removals in milk and calf production, fodder and live weight gain.

Several large dairies that were designed in accordance with the core elements of BMP are currently being commissioned.  RSSA, as part of the program, will assess the benefits afforded by BMP in relation to the local natural resource management action targets and resource conditions.  The action targets and resource conditions will enable RSSA to compare nutrient and water conservation figures with specific natural resource management benchmarks.