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Guide 20
Guide 2017
Slurry is a valuable source of organic nitrogen, potassium, and potash and, when used correctly, can reduce fertiliser bills on
farms and raise profitability
It is paramount to apply when ground conditions allow, and
to use on fields that need it most; typically, silage fields which
have a higher potassium (K) and phosphorus (P) requirement
than grazing ground; crops with a high demand for P and K; or
on fields that are low in P and K.
What is the value of cattle slurry?
The nutrient content of cattle slurry varies with animals' diet and
with dilution of water. Typically, 1,000 gallons of cattle slurry is
equivalent to a 50kg bag of 6-7-30, depending on the time of
year it is applied, weather conditions and method of application.
Teagasc estimates slurry to be worth 25/1,000 gallons. Its true
value depends on current fertiliser prices and the volume of
fertiliser it can replace.
Nitrogen (N) is, typically, present in both the solid and liquid
fraction of the slurry. Half of the N in cattle slurry is in organic
form and the other half is present as ammonium (similar
to purchased bagged N). Thus, its availability to the crop
is very weather dependent. Slurry applied in the spring is
worth, approximately, an extra three units of N per 1,000 gallons
compared with summer application due to volatilisation.
Diluting slurry with water will improve the N uptake as the slurry
will penetrate faster into the soil compared to thick slurry. Plus,
diluted slurry will be washed-o the grass faster resulting in
reduced grass contamination. But, water will reduce the P and
K content of the slurry. It is advised to apply cattle slurry under
cool, moist weather conditions (eg. spring rather than summer)
as this will increase the amount of ammonium that is captured
by the crop and, therefore, increases the organic fertiliser value.
Also, the method of slurry application has an e ect. Using low-
emission slurry spreading technology such as Trailing Shoe,
Tri-App or Shallow Injection as against Splash Plate will also
increase N utilisation and value. These methods will typically
improve N availability by 30-50 per cent.
P is in the solid fraction and K is in the liquid fraction of the
slurry. Typically, 85 per cent of the value of slurry is in the
P and K value. The rate of release of P and K from organic
manures depends on the soil's P and K status. According to
Teagasc, when soils are at a P index of 1-2, it is best to apply 50
per cent in the form of organic manure and the remainder as
artificial fertiliser. At P index of 3-4, slurry can be used to supply
100 per cent of the P requirements. In relation to K, Teagasc
recommends 75 per cent of crop requirements as slurry when
the K status is 1-2. While at a K index of 3-4, then slurry can
supply 100 per cent of the crop's requirements.
Thus, a soil test to determine the soil's P and K status helps
to target slurry to Index 1 and 2 soils for more e cient crop
fertilisation and P and K utilisation.
Michael A O'Grady
Abbey Machinery
Slurry management
getting more from your slurry
Abbey 3500 tank at JCB Farmtrac demo.