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Save Fertiliser Dollars With Dairy Effluent

Every dairy farm produces effluent and with the current high cost of fertiliser, it is actually a valuable resource if effectively utilised on the farm.

By Department of Primary Industries - 26th March 2009 - Back to News

Department of Primary Industries (DPI) advises if applied carefully to pastures and crops, it can satisfy Environment Protection Authority policy requirements to contain effluent within a farm’s boundaries and importantly save money on fertiliser.

Nutrient value of effluent

Dairy effluent contains nitrogen, phosphorus, potassium and a range of other nutrients. Many farms have a two pond effluent system, where the second pond is emptied most frequently.

Research conducted over the last five years by DPI’s Gippsland Nutrient Extension Team has found that the average nutrient values per megalitre of second pond effluent are as follows:

• Nitrogen: 200 kg nitrogen;
• Phosphorus: 52 kg phosphorus; and
• Potassium: 395 kg potassium.

It should be noted however, that the concentration of nutrients varies widely around these averages due to many factors, such as water use in the dairy, cow numbers, feeding regime and also pond cleaning frequency. The majority of nutrients in liquid effluent are available for plant use.

To put these nutrient values into perspective, an average dairy farm can produce around five megalitres of second pond effluent per year.

Using recent fertiliser prices of common nitrogen, phosphorus and potassium fertilisers this equates to approximately $1,660 of nutrient value in each megalitre of dairy effluent, less any cost involved in spreading the effluent.

Cost of fertiliser

Fertiliser prices used to calculate cost per kg of nutrients were as follows (including GST, but excluding delivery and spreading):

• Nitrogen: Urea: $847/tonne = $1.84 /kg N;
• Phosphorus: Superphosphate: $591/tonne = $6.72/kg P; and
• Potassium: Muriate of potash (MOP): $1191/tonne = $2.38 /kg K.

This effluent can be strategically used to reduce the farm fertiliser bill, while satisfying your requirements to keep effluent within your farm boundaries.

Nutrient value of sludge

In a two pond system the recommendation for the first pond is to desludge every two to four years.

An example of research done at DemoDAIRY in South West Victoria, where the first pond was desludged between five and seven years ago, showed that this farm’s first pond sludge contained approximately 1000 kg nitrogen/ML, 192 kg phosphorus/ML and 625 kg potassium/ML.

Using the fertiliser prices and nutrient levels above this means one megalitre of sludge in this example was worth approximately $4,600, less spreading costs. Sludge has more slow release nutrients than liquid effluent, which means that applying sludge will also produce benefits into the future as nutrients become available.

An example analysis of solids taken from a trafficable solids trap contained 1,400 kg nitrogen/ML, 460 kg phosphorus/ML and 1200 kg potassium/ML.

As you can see, your dairy effluent is a very valuable resource and can help save you dollars on fertilisers.

For more information or if you would like your dairy effluent tested and analysed, please contact your nearest DPI Nutrient Extension Officer at DPI Ellinbank on 5624 2222 or DPI Maffra on 5147 0800.

Source: http://gippsland.com/

Published by: news@gippsland.com

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