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Farm dairy effluent

  • If you wish to achieve 100% compliance with the regional council requirements at all times you must have the appropriate philosophy. If you believe farm dairy effluent should be disposed of, you may be on the wrong track.

  • Monitor for N and K levels of the effluent (most labs can analyse effluent N & K) 2-3 times per season to maximise the fertiliser benefit of the farm dairy effluent. Monitoring for N & K becomes more critical for sludge or effluent from wintering barns which have greater levels of N, P and K than farm dairy effluent.

  • The moment you are convinced farm dairy effluent is actually a valuable liquid fertiliser, your management of the effluent will become more proactive and efficient than being reactive. Farm dairy effluent is an excellent source of N, P and K.

  • It is important that you design your irrigable area to maximise the benefit of potassium (K) than nitrogen (N). Farm dairy effluent is an excellent source of K than N. If effluent is applied to obtain K benefits N loading of effluent reduces consequently and substantially.

  • On average, a 200 cow herd farm could provide 1080 kg N (nitrogen), 1350 kg K (potassium) and 135 kg P (phosphorus) per milking season.
  • Based on the current fertiliser market price the N, P and K fertiliser value of the farm dairy effluent for a 200 cow herd farm is around $3600 per milking season.
  • The important factor in considering K as a primary source of effluent nutrient is that if K is applied excessively through effluent irrigation, pasture grown in effluent irrigation area will be deficient in Mg (magnesium). Mg deficient pasture could cause metabolic problems in cows.

  • If you wish to find out K loading rate per ha for farm dairy effluent you can use the simple ENVIROKNOWLEDGE® equation: Regional Council Permitted Activity N loading rate/ha x K level in effluent ÷ N level in effluent.
  • Based on a typical annual K fertiliser application rate of 75 kg K/ha, an effluent with N and K levels of 400 and 600 mg/L respectively should be applied over a 3 ha area rather than the usual 1 ha. This will result in an annual N loading rate of 50 kg N/ha with a one-off effluent application rate of 12.5 mm.
  • Have adequate effluent storage designed to cope with saturated soil conditions.

  • Prepare effluent storage for the milking season by emptying and repairing any leaks prior to the milking season.

  • Apply effluent at or below the rate specified by the regional councils depending on your farm or paddock nutrient requirements.

  • Avoid effluent runoff or applying effluent under saturated conditions.

  • If you have tile/mole drains ensure effluent does not enter the drains and use low rate irrigators such as K-lines.

  • Minimise water use at the farm dairy to improve effluent storage capacity.

  • Divert storm water (roof water) from effluent storage systems.

  • Sludge collected from herd barns/houses or effluent storage will have greater N, P and K than farm dairy effluent. It pays to get the sludge analysed before applying. Several composite samples thoroughly mixed to create one sludge sample analysis may incur a laboratory cost of $45-70 for collective N, P and K analyses.

  • Given the less runny nature, sludge can be applied to cropping or fodder or ploughed soils or composted. Alternatively it can be diluted with water and screened and applied through conventional irrigation systems onto pasture.