Know your limits on fertiliser

As farmers across the country spread fertiliser on spring and winter crops, it is essential that you are providing those crops with what they need and also to make sure that you do not exceed nitrogen and phosphorus limits.

Nitrogen

Table 1 below shows the fertiliser allowance for different crops based on the soil index. Index 1 applies to a previous crop of cereals or maize and index 2 refers to fields after potatoes, beet, oilseed rape, peas and beans.

Crops five years out of grass fall into index 1. Crops one and two years out of grass are in index 4 if they were grazed-only and fall into index 3 if they were cut-only. Index 2 applies to fields three and four years out of grass if they were cut-only.

If you have proof of higher yields in one of the past three years (based on 20% moisture content) than the reference yields outlined then you can apply another 20kg/ha (16units/ac) for every tonne per hectare over the reference yield. If you had cover crops in the previous year, you can decide to up or down rates based on how good the crop was, but do not cut by a whole lot.

Phosphorus

Phosphorus (P) application is based on your soil tests. If you do not have in date soil test results (taken within five years) then you cannot apply P.

See Table 2 for P guidelines from Teagasc. For every tonne over the yields outlined then you can apply another 3.8kg/ha of P. If you are in index 4 and your soil pH is 7 or over then you can apply 20kg/ha of P (16 units/ac).

Potassium

There is no limit to potassium application, but you should still stay within the recommendations to use it efficiently.

You can increase or decrease the level applied depending on your crop type and your crop yield (see Table 3 for more details).