Use up P fertiliser stocks on farm

Silage making is in full swing and decisions must be made now on fertiliser type for second cut. Several issues are coming to the fore such as potash and sulphur deficiencies and concern regarding future phosphorus regulations. Unfortunately most farmers do not have a recent soil analysis on which to base their fertiliser decisions. So what should be applied?

Silage swards are commonly low in potash, which can lead to reduced yields. Silage swards can quickly become deficient in potash, particularly if low rates of potash fertiliser or slurry are applied. The recommended amount of potash to be applied varies significantly depending on fertility status but typically 90-100 kg/ha needs to be supplied in fertiliser and organic manures.

Sulphur levels are falling and increasingly this nutrient is becoming deficient. Deficiencies were traditionally found in second cut silages on sandy soils only, but now they can also occur in all cuts and on most soils. Apply a fertiliser that contains sulphur.

Soil phosphorus levels, in contrast, are adequate or in excess for most silage fields. Deficiencies are uncommon and if slurry is being applied, no phosphorus fertiliser should be required.

One of the key measures agreed within the Nitrates Directive Action Programme is that phosphorus fertiliser can only be applied if a need has been identified through a soil analysis. The introduction of these Regulations is anticipated for later this year. It is important, therefore, for farmers to realise that any unused phosphorus fertiliser carried over to next year could only be applied if a need was identified through a soil analysis. If no need can be demonstrated, then phosphorus containing fertilisers cannot be applied.

Applying nutrients to the required level has always been good practice and the key to good sward growth; it is soon going to be a legal requirement also.