The importance of this will partly depend on where that nitrogen level places you relative to the Soil Nitrogen Supply Index system. If you are between indices, this may affect the recommendation by 40 kg N/ha in RB209. If this figure is not known, then the field assessment method or software such as N Plan can be used.

In one site during 2006, RB209 gave a recommendation of 100 kg N/ha, compared to N Plan at 142 kgN/ha. The two treatments were trialled against a third treatment of 160 kgN/ha. The results clearly demonstrated that RB209 is not robust enough to suit every site and any changes to legislation must allow other systems as supplementary guidance.

In this example, the RB209 recommendation cost the farmer 1.8 t/ha – a staggering £153/ha – with N Plan giving the optimum result. It is important to note that there is nothing in place that only allows RB209 recommendations.

RB209 is one authoritative source, but not the only information that you can use if you need further guidance. You should be able to explain which system you have used, or how you have arrived at the crop requirement for fertiliser nitrogen.

N Plan is now available on CD or via the Yara website.