How to account for winter rainfall in nutrient management plans

Winters are getting wetter and this impacts nutrient management. Jason Pole examines the latest excess winter rainfall (EWR) data and how to use it alongside our Nutrient Management Guide (RB209).

Wet winters are a characteristic of our temperate climate, but if you think they are getting wetter, you are right.

A 2024 report on the UK climate examined data from 1767 onwards and found that six out of the ten wettest winters for England and Wales occurred this century (based on the full winter rainfall period: October to March).

Although the previous winter rainfall period (2024/25) had a soggy start, its dry end was more notable (which marked the start of prolonged dry-weather periods across the UK).

So far, the current winter has seen significant rainfall accumulation in many areas, which is a mixed blessing, because:

• It is boosting depleted groundwater and reservoir levels
• Water lost through field drains takes nitrate with it

And, unlike last year, the rain clouds keep coming.

To indicate potential nitrate losses in drainage water, we publish excess winter rainfall (EWR) data.

Based on Met Office data, the figures show accumulated rainfall over October to March, which is a proxy for the actual EWR period.

The actual EWR period, which depends on local weather and site conditions, starts when the soil profile becomes fully wetted in the autumn (field capacity) and ends when drains stop flowing in the spring.

We show the EWR results in a UK grid (comprising 199 squares, each measuring 40 km by 40 km) using three categories:

• Low EWR: less than 150 mm
• Moderate EWR: 150 to 250 mm
• High EWR: over 250 mm

These categories align with look-up tables in the Nutrient Management Guide (RB209) that help you estimate soil nitrogen supply (SNS) in various cropping situations.

Each year, we release interim EWR results in February to highlight emerging trends.

In a typical year, most UK grid squares max out as ‘high’ by the end January, especially in a bare-soil scenario.

It holds true this winter, with most bare-soil squares already in the high category (176) at the end of January, with the remainder marked as moderate (22) or low (1).

We also present EWR data that accounts for evaporation from winter crops (wheat, barley and oilseed rape) and grass.

Results are similar between cereals and grass, with a slightly greater drying effect in the latter, but not quite as much as in winter oilseed rape.

When accounting for evapotranspiration in oilseed rape, the number of ‘high’ squares reduces slightly (142), with a more in the moderate (34) and low (23) categories.

Consistent with long-term trends, the driest areas mainly cluster around the East of England.

Interestingly, the category distribution is already similar to the whole EWR period in 2024/25.

Bearing in mind the wet start of February in many areas (see this Met Office blog for details) and more rain is forecast, the 2025/26 EWR period is on track to be wetter than the last.

The final EWR data in April will reveal how much wetter.

To plan and refine nitrogen applications (including in response to expected yields), follow RB209 guidance.