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Grass Silage/Hay

N fertiliser advice for cut swards

Rates of fertiliser N are shown as kg/ha

Table 1:- Nitrogen Rates for Cut Swards
CropN application rate (kg/ha)
Silage (1st Cut) 100
Silage (2nd or subsequent cuts) 80
Hay 65 - 80

Rates shown above refer to application of available N. Chemical fertilizer rates should be calculated by deducting the available N contained in organic fertilizer applications from the rates shown in the table above.
If N is applied for early grazing, assume that 20% of this remains available for first cut silage.
An extra 25 kg/ha may be used where necessary for establishment of a good ryegrass sward if pasture is less than 4 years old, provided that the maximum N allowed within the nitrates regulations is complied with.
Where silage fields were grazed rather than cut in the previous year, apply 100 kg/ha for first cut, and 85 kg/ha for second and subsequent cuts.
When more than 2 cuts are taken there is a danger that the allowance in the nitrates regulations will be exceeded.
Less N is advised for hay crops when there is a high risk of crop loss due to high rainfall

P and K for silage

Phosphorus (P) and Potassium (K) for silage

Table 2:- P and K requirements (kg/ha) for grass silage. (Rates shown are total requirements, before deductions for organic fertilisers).

Soil IndexCut Once2nd and subsequent cuts
 P (kg/ha)K (kg/ha)P (kg/ha)K (kg/ha)
1 40 175 10 70
2 30 150 10 55
3 20 120 10 35
4 0 0 0 0
  • Silage crops remove more P and K from fields than grazing. Each 1 tonne of grass silage will remove 4kg P and 25kg K per tonne of grass dry matter, respectively.
  • Where swards are being harvested for silage, apply the rates of P and K shown below in addition to the grazing requirements.

Fertiliser Values for Cattle Slurry

Cattle slurry is a valuable source of N, P & K and should be applied to silage fields to ensure the return of P and K. This will help maintain P and K levels for optimum production in the farms silage area.  Cattle slurry has the correct P : K ratio for fertilising the grass silage crop.  Table 4 below shows the N, P & K value of slurry and the effect of LESS on slurry N recovery.  33m3/ha of good quality cattle (6% DM) will slurry sufficient P & K to grow a crop of 1st cut silage on Index 3 P & K soils.  On Index1 & 2 soils reduce P and K availability by 50% and 10%, respectively.  On Index 1 & 2 soils use a high N low P & K fertiliser blend (27’s or 24’s) to complement the P & K in cattle slurry to ensure the crop has sufficient levels.  It is also important to take account of any P & K applied to silage fields prior to closing for silage for example silage ground maybe grazed and may have received an application for example of 18-6-12 in March which will help feed the current silage crop.  See table 5 for suggested fertiliser programmes with and without slurry.

Suggested Fertiliser (N, P & K) Programme for 1st Cut Grass Silage (Fertiliser Only)

 Table 3. N, P & K requirements for 1st Cut Grass Silage (5t/ha DM) & suggested fertiliser programmes

*The P and K rates shown can be supplied by either slurry or fertiliser