Farm Ireland
Independent.ie

Thursday 23 February 2017

Make most of your on-farm slurry

With chemical fertiliser prices on the rise, nutrient-rich manure can boost the soil needs of your fields

Caitriona Murphy

Caitriona Murphy

Fields low in phosphorus and potassium need to be targeted to receive slurry
Fields low in phosphorus and potassium need to be targeted to receive slurry
Overcast days with little sun and no wind are ideal for spreading slurry

Making maximum use of slurry as a source of nutrients could be described as a 'no-brainer' for farmers in any year, but it is particularly critical in a year like this when prices for chemical fertiliser are on an upward trajectory.

Teagasc grassland experts Michael O'Donovan, Emer Kennedy and Pearse Kelly have some essential advice for farmer on how to get the most out of slurry this year.

They say that as a valuable source of nitrogen (N), phosphorus (P) and potassium (K), cattle slurry should be applied on the fields that need it most and at the time of year that will give you the best response.

"All of the P and K in slurry is available to be used, and fields that are low in both these nutrients need to be targeted to receive slurry," says Michael O'Donovan.

"On a lot of farms, this will be the silage fields as this is where the feed that eventually produced the slurry came from in the first place."

While the time of year that slurry is spread does not affect the availability or usage of P and K, this is not the case with N.

Half of the nitrogen that is contained in cattle slurry is in an organic form and the other half is contained as ammonium -- the same substance that is in purchased urea fertiliser. It is this ammonium content that farmers can use to replace bought in bagged N.

"Similar to urea fertiliser, there are times of the year that you can expect to get the maximum value of nitrogen from slurry, and this is very much weather dependent," adds Mr O'Donovan.

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Difference

The ideal conditions for getting the best nitrogen usage from cattle slurry are:

n Overcast with little sunshine;

  • Slight drizzle of rain;
  • Little or no wind.

The difference in nitrogen usage varies hugely, depending on the weather conditions at the time. When weather conditions are only average, there is a 50pc loss in the usage rate. Where the conditions are poor, such as on a dry sunny day with a strong breeze, there is a further 50pc loss in the usage rate.

"A good rule of thumb is that a day that is very good for drying clothes on a washing line is a bad day for spreading slurry if you want to get the maximum amount of N in it used," says Mr O'Donovan.

For example, a spring application of 2,500ga of cattle slurry on an overcast, drizzly day with no wind would deliver a usage rate of 24 units of N/ac.

However, on a bright day with a slight breeze, this could fall to 12 units of N/ac, and on a warm, sunny day with a strong breeze, it could fall further to just six units of N/ac.

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