October 2002 Dairy effluent: Flood irrigation of dairy AG0426 shed effluent ISSN 1329-8062 Scott McDonald, Kyabram

Dairy shed effluent is a natural fertiliser and soil However, with significant variations in results, due to conditioner and if managed effectively can enhance factors such as; age of effluent ponds, whether the sample pasture growth and improve soil structure. was taken from the first or second pond or seasonality a Farms that have internal irrigation systems designed to more accurate application rate can only be achieved by flood irrigate pastures, have an opportunity to distribute sampling your own effluent system and determining the nutrients back to pastures, in a productive and nutrient concentration. sustainable manner. Whole Farm Plans Effluent ponds need to be emptied during the irrigation Preparation of a whole farm plan is highly recommended season, so that there is enough storage capacity to before you alter or develop your effluent system, as this contain effluent over the wetter months. will ensure that the effluent system is incorporated into the Care should be taken when flood irrigating to ensure that irrigation layout effectively. any runoff containing effluent does not leave the farm. Turkey nest ponds in particular need to be constructed Shandying Effluent with Channel Water close to farm irrigation channels on a site that will enable effluent to be conveyed by gravity into the farm irrigation The optimum time to discharge effluent into farm channels system. is when fresh water is flowing passed. Applying effluent Whole farm plans also provide the opportunity to clearly shandied with irrigation water immediately following define which pastures are accessible for effluent grazing is recommended, as there is an opportunity to apllication, which is a key consideration when selecting a utilise the nutrients in the regrowth of plants. It also pond site. enables pasture palatability to return before the next grazing. A withholding period of 14 days is recommended For further information on whole farm plans contact DPI following effluent application. A longer period may be Echuca. required following the application of slurry. Reuse Systems Alternatively applying effluent directly to the top of the bays prior to irrigation has limitations in that a large It is best practice to apply effluent on irrigation bays, amount of nutrients may be applied to a small area. where runoff is collected by the farm's reuse system, thus preventing effluent from leaving the property. A key feature in utilising the farms irrigation system is to ensure effluent is shandied close to irrigation water supply Drainage reuse systems are usually not designed for point, since this is a point at which effluent can be applied effluent storage and therefore effluent should not be to a large area. conveyed directly from the shed to the reuse storage. Nutrient buildup in reuse dams, promoting the likelihood Area of Land Needed of blue green algae blooms is more likely if dairy effluent Dairy effluent must be applied over a significant area of is allowed to enter the reuse system. the farm to prevent soil nutrient overloading. As a rule of Occasionally effluent ponds are sited close to reuse thumb, it is recommended that dairy shed effluent be systems, so that effluent can be distributed over a broader applied over at least 10% of the milking pasture. area of the farm, which can be achieved via the reuse This recommendation is based on effluent nutrients tests pump. Effluent should therefore only enter the reuse dam, sampled from pond systems across the SouthWest and when the reuse water is being pumped back into the Northern Irrigation regions of Victoria. On average 1ML irrigation cycle. of effluent from storage ponds will contain, 180KgN, As drainage reuse systems are often located close to the 31KgP and 420KgK. regional drainage system, effluent should be flushed out of

© State of Victoria, Department of Primary Industries Page 1 Dairy effluent: Flood irrigation of dairy shed effluent AG0426 these and irrigated onto pastures to prevent the likelihood Effluent remaining in the farms irrigation channels provide of effluent leaving the property during a heavy rain event. ideal nutrient and water conditions and thus promotes Water containing effluent can not be released from a reuse weed growth. dam by law into the regional drainage system. A build up of effluent in the channel is also common, and Therefore using reuse systems as a means of redistributing together with weeds will restrict the flow of irrigation effluent nutrients back to pastures is generally not a water, thus hindering the irrigation effectiveness. preferred option. Constant channel cleaning to remove effluent and weed growth, may eventually lead to widening and deepening of Shandying Effluent with Ground Water channels which will interfere with water flow in the Farmer's shandying effluent with ground water should take channel system. care, due to the relatively high levels of electrical A good practice is to flush farm channels of any effluent, conductivity (EC) salts present in dairy effluent. before completing the irrigation cycle. Samples taken from effluent ponds have indicated an average reading of 4680us/cm, which is well above the Single Storage Turkey Nest System recommended 800 us/cm for irrigation water for maximum An effluent system common for dairy farms operating in productivity. Therefore shandying effluent with poor irrigated regions of Victoria is a single storage turkey nest quality ground water may magnify the problem severely pond, which enables effluent to be shandied into the farm affecting pasture performance and soil health. irrigation channel during irrigation. Nutrients are applied Dual effluent ponds, designed for recycling effluent back back to pastures in an economical and sustainable manner. to yard washing systems, will have a higher concentration Key feature of the effluent system. of salts. In these systems, it is better to apply smaller • amounts of effluent over a much larger area. Single pumping application. • Storage located close to irrigation water supply source Ponds should also be emptied more frequently, to avoid to enable effluent to access a larger percentage of the high EC levels in the ponds, which will affect the farm pastures. anaerobic process. • Above ground storage reducing the potential to pollute Open Drains and Farm Channels ground waters. • Effluent contained until irrigation is scheduled. Allowing effluent to sit in farm channels or constantly • Deep anaerobic design to enhance pond functioning. overflowing into them should be avoided.

Figure 1. Single storage turkey nest

The advice provided in this publication is intended as a source of information only. Always read the label before using any of the products mentioned. The State of Victoria and its employees do not guarantee that the publication is without flaw of any kind or is wholly appropriate for your particular purposes and therefore disclaims all liability for any error, loss or other consequence which may arise from you relying on any information in this publication.

© State of Victoria, Department of Primary Industries Page 2