Effective use of fertilser for second cut
W R McCulloch, Dairying Development Adviser, Ballymoney, College of Agriculture, Food & Rural Enterprise
Silage making will soon be in full swing so now is the time to decide which fertilisers to apply for second cut. Soil fertility and availability of slurry will have the major influence on this choice.
Many farms participating in the Countryside Management Scheme have carried out soil analysis. Make use of this information to plan cost effective use of fertilisers. 100kg nitrogen (N)/hectare (80 units/acre) is the normal recommendation for second cut on productive swards with a high content of sown species. However, phosphate (P) and potash (K) recommendations vary according to soil reserves. The P & K requirements for soils at various indices are given in Table 1.
Table 1 – P & K Recommendations for 2nd cut
| Soil Index | 0 | 1 | 2 | 3 | >3 |
|---|---|---|---|---|---|
| P kg/ha | 25 | 25 | 25 | 0 | 0 |
| K kg/ha | 120 | 100 | 75 | 40 | 0 |
The table indicates the total P & K requirements for 2nd cut. Allowance has to be made for the N, P & K content of any slurry applied before deciding what fertiliser needs to be applied. For example a field with a typical soil analysis of P index 2 and K index 1 requires 100 kg N : 25 kg P : 75 kg 12/hectares (80 units N : 20 units P : 60 units K/acre).
If 22,500 litres of cow slurry/hectare (2,000gallon/acre) are applied, the nutrients available for grass growth will be 13.5 kg N : 27 kg P : 72 kg K. While the P in the slurry will meet the crops P requirements, an additional 86 kg N and 28 kg K will have to be applied as fertiliser. 7.5 bags/hectare (3 bags/acre) of a high N : high K compound such as 21.0.14 could be used, with a small surplus of potash being applied.
If no slurry is available for application, then the option would be to apply 7.5 bags/hectare (3 bags/acre) of a high potash compounds such as 24.6.12 with additional potash applied as a separate dressing of muirate of potash (60% K) at a rate of 1.25 bags/hectare (1/2 bag/acre).Sulphur deficiency is now quite common in 2nd and 3rd cut silages so it is recommended to use compounds containing sulphur for these later cuts.
Nutrient management will be increasingly important once the Nitrates Action Programme is implemented. Training on this subject is available through CAFRE. Speak to your local development adviser for further details.