Flood irrigation of dairy effluent

Note Number: AG0426
Published: October 2002
Updated: July 2009

Dairy effluent is a natural fertiliser and soil conditioner and if managed effectively can enhance pasture growth and improve soil structure.

Farms that have internal irrigation systems designed to flood irrigate pastures, have an opportunity to distribute nutrients back to pastures, in a productive and sustainable manner.

Effluent ponds need to be emptied during the irrigation season, so that there is enough storage capacity to contain effluent over the wetter months.

Care should be taken when flood irrigating to ensure that any runoff containing effluent does not leave the farm.

Shandying Effluent with Channel Water

The optimum time to discharge effluent into farm channels is when fresh water is flowing passed. Applying effluent shandied with irrigation water immediately following grazing is recommended, as there is an opportunity to utilise the nutrients in the regrowth of plants. It also enables pasture palatability to return before the next grazing. A withholding period of 14 days is recommended following effluent application. A longer period may be required following the application of slurry.

Alternatively applying effluent directly to the top of the bays prior to irrigation has limitations in that a large amount of nutrients may be applied to a small area.

A key feature in utilising the farms irrigation system is to ensure effluent is shandied close to irrigation water supply point, since this is a point at which effluent can be applied to a large area of the farm.

Due to seasonal uncertainty regarding irrigation availability farmers should adopt a more strategic emptying of pondage systems to match the limited irrigation events.

Area of Land Needed

Dairy effluent must be applied over a significant area of the farm to prevent soil nutrient overloading. As a rule of thumb, it is recommended that dairy shed effluent or other significant point sources such as feedpads be applied over at least 10% of the milking pasture. This will however, require a close monitoring of soil fertility.

This recommendation is based on numerous effluent nutrients tests sampled from pond systems across Victoria. On average 1ML of effluent from storage ponds will contain, 430KgN, 114KgP and 450KgK.

However, with significant variations in results, due to factors such as; age of effluent ponds, whether the sample was taken from the first or second pond or seasonality a more accurate application rate can only be achieved by sampling your own effluent system and determining the nutrient concentration.

Agitated ponds will have a significantly higher nutrient concentration prior to irrigation, due to nutrients sitting in the sludge layer being raised.

Whole Farm Plans

Preparation of a whole farm plan is highly recommended before you alter or develop your effluent system, as this will ensure that the effluent system is incorporated into the irrigation layout effectively.

Turkey nest ponds in particular need to be constructed close to farm irrigation channels on a site that will enable effluent to be conveyed by gravity into the farm irrigation system.

Whole farm plans also provide the opportunity to clearly define which pastures are accessible for effluent application, which is a key consideration when selecting a pond site.

For further information on whole farm plans contact an Irrigation Modernisation Officer at DEPI Echuca, Kerang or Tatura.

Reuse Systems

It is best practice to apply effluent on irrigation bays, where runoff is collected by the farm's reuse system, thus preventing effluent from leaving the property.

Drainage reuse systems are usually not designed for effluent storage and therefore effluent should not be conveyed directly from the shed to the reuse storage.

Nutrient buildup in reuse dams, promoting the likelihood of blue green algae blooms is more likely if dairy effluent is allowed to enter the reuse system.

Occasionally effluent ponds are sited close to reuse systems, so that effluent can be distributed over a broader area of the farm, which can be achieved via the reuse pump. Effluent should therefore only enter the reuse dam, when the reuse water is being pumped back into the irrigation cycle.

As drainage reuse systems are often located close to the regional drainage system, effluent should be flushed out of these and irrigated onto pastures to prevent the likelihood of effluent leaving the property during a heavy rain event.

Water containing effluent can not be released from a reuse dam by law into the regional drainage system.

Therefore using reuse systems as a means of redistributing effluent nutrients back to pastures is generally not a preferred option.

Shandying Effluent with Ground Water

Farmer's shandying effluent with ground water should take care, due to the relatively high levels of electrical conductivity (EC) salts present in dairy effluent.

Samples taken from effluent ponds have indicated an average reading of 4680us/cm, which is well above the recommended 800 us/cm for irrigation water for maximum productivity. Therefore shandying effluent with poor quality ground water may magnify the problem severely affecting pasture performance and soil health.

Dual effluent ponds, designed for recycling effluent back to yard washing systems, will have a higher concentration of salts. In these systems, it is better to apply smaller amounts of effluent over a much larger area.

Ponds should also be emptied more frequently, to avoid high EC levels in the ponds, which will affect the anaerobic process.

Open Drains and Farm Channels

Allowing effluent to sit in farm channels or constantly overflowing into them should be avoided.

Effluent remaining in the farms irrigation channels provide ideal nutrient and water conditions and thus promotes weed growth.

A build up of effluent in the channel is also common, and together with weeds will restrict the flow of irrigation water, thus hindering the irrigation effectiveness.

Constant channel cleaning to remove effluent and weed growth, may eventually lead to widening and deepening of channels which will interfere with water flow in the channel system.

A good practice is to flush farm channels of any effluent, before completing the irrigation cycle.

Single Storage Turkey Nest System

An effluent system common for dairy farms operating in irrigated regions of Victoria is a single storage turkey nest pond, which enables effluent to be shandied into the farm irrigation channel during irrigation. Nutrients are applied back to pastures in an economical and sustainable manner.

Key feature of the effluent system

• Single pumping application.
• Storage located close to irrigation water supply source to enable effluent to access a larger percentage of the farm pastures.
• Above ground storage reducing the potential to pollute ground waters.
• Effluent contained until irrigation is scheduled.
• Deep anaerobic design
• to enhance pond functioning.

Figure 1. Single storage turkey nest

Acknowledgements

This Agnote was developed by Scott McDonald, October 2002.

It was reviewed by Scott McDonald, Farm Services Victoria. July 2009.

ISSN 1329-8062

Published and Authorised by:
Department of Environment and Primary Industries
1 Spring Street
Melbourne, Victoria

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