Applying a spring slurry application could provide some, or all of your Nitrogen, Phosphate, Potash and Sulphur requirements for first cut silage. Consequently it’s important to do the maths before deciding on type of inorganic fertiliser to apply.
A rule of thumb for cattle slurry is that 1 m3 contains
1.0 kg of available Nitrogen (N),
1.2 kg of Phosphate (P)
2.5 kg of Potash (K).
The NPK nutrient requirements of a 1st cut silage crop depending on the quantity of silage required (and the swards yield potential.) For example:-
100 kg/ha of N.
40 kg/ha of P.
80 kg/ha of K.
If you know the quantity of slurry applied you can calculate the fertiliser contribution from the applied slurry using the values above. Example: 20 m3/ha of slurry applied equates to
Nitrogen 20 kg (20 x 1.0)
Phosphate 24 kg (20 x 1.2)
Potash 50 kg of K (20 x 2.5).
Subtracting these values from those required provide a value for each element either in demand or surplus
Element Required Applied +/-
Nitrogen 100 20 80
Phosphate 40 24 16
Potash 80 50 30
Now where did I put the last soil analysis for the field and how old is it?
Best products to use are compounds with a uniform particle size. A blend will work but has a few drawbacks in use.
Sulphur containing fertilisers can improve yield, sulphur is a necessary component for protein synthesis in grass. Its uptake results in yield increases averaging 15% whilst simultaneously improving grass protein and sugar concentrations. This too needs adding to the calculations.
Since most of the costs associated with making silage are on a /ha basis, by optimising the yield you can reduce the overall cost per tonne.
