Potential to cut back on nitrogen applied to cereals and oilseed rape

Relatively dry winter conditions across most of the UK mean farmers could potentially reduce the amount of nitrogen fertiliser applied to cereals and oilseed rape.

The extent of the ‘low’ and ‘moderate’ excess winter rainfall (EWR) zones is much wider this year, spreading further up the eastern coastline and more inland than average.

EWR is the rainfall between the time when the soil profile becomes fully wetted in the autumn and the end of drainage in the spring.

As lower EWR is associated with higher levels of residual soil nitrogen, AHDB has urged farmers to follow the Nutrient management guide, also referred to as RB209, to fine-tune remaining nitrogen applications.

The guide describes how to estimate a field’s soil nitrogen supply (SNS) index by the Field Assessment Method.

In addition to information on soil type and the previous crop, the method requires an estimate of the rainfall range for the field.

AHDB says this should ideally be based on EWR, as it provides a good indication of the potential loss of nitrate through leaching.

The final EWR estimates are based on data from 1 October 2018 to 31 March 2019, averaged over 199 (40 km by 40 km) regions. For each of these regions, a colour-coded UK map highlights the RB209 EWR category:

• Low – less than 150 mm EWR (annual rainfall less than 600 mm)

• Moderate – 150 to 250 mm EWR (annual rainfall between 600 to 700 mm)

• High – over 250 mm EWR (annual rainfall over 700 mm)

• Despite the relatively dry winter, 31 of the 199 regions still had EWR in excess of the long-term average (1981–2010). These were mainly situated on the west coast of England, Wales and Scotland.

Sajjad Awan, who manages nutrient research at AHDB, said that by early February, it already looked like it was going to be an exceptionally dry winter.

“Although there have been some significant spells of rain since then, particularly during early March, it has remained relatively dry, for most. In fact, the East coast of Scotland has just experienced its driest winter since 1964,” he said.

“All nutrient management plans should now be revisited. It’s particularly important to do this for spring malting barley crops, because these need to be grown to meet tight grain nitrogen band specifications.”