Nitrogen management in RL trials

Paul Gosling explains how the Nutrient Management Guide (RB209) helps set fertiliser rates in the trials for the Recommended Lists for cereals and oilseeds (RL).

Norfolk site

This year, we are focusing on a winter wheat RL trial site in Norfolk (Terrington St Clement) to bring the RL trial protocols to life.

The site includes a fungicide treated trial with 50 varieties (35 recommended, 15 candidates) replicated three times (150 variety plots in total). We carefully manage all inputs to ensure that no variety is disadvantaged.

The Terrington site is just one of 31 winter wheat fungicide treated yield trials across the UK for harvest 2025, which is why the RL protocols cannot be too prescriptive.

This is particularly important when site specifics determine the best management approach, as is the case with nutrition.

The RL protocols state that trial operators should “take into account inherent fertility, previous cropping, winter rainfall, best local practice and advisory guidelines.”

RB209 guidance is important because it helps RL trial operators tailor application rates to maximise grain yield and consider other key factors, such as grain protein targets (for feed, bread or biscuits) and nitrate vulnerable zone (NVZ) regulations.

The Terrington site (which is not in an NVZ) has deep, fertile, silt soils and a very high yield potential.

In 2022, the average fungicide treated winter wheat yield was over 15 t/ha (198 kg/ha of nitrogen applied following a pea crop).

Nitrogen rates

The harvest 2024 trial received much more nitrogen than in 2022, partly due to the site’s high yield potential.

It was also due to high excess winter rainfall and because the winter wheat followed sugar beet. This dropped the soil nitrogen supply (SNS) index to 1 (estimated by RB209).

In this scenario, RB209 recommends a nitrogen rate of 210 kg/ha for an 8 t baseline crop, with an extra 10 kg/ha for each 0.5 t/ha increase in potential yield up to 13 t/ha.

This resulted in 310 kg/ha nitrogen applied to target yield in 2024.

The harvest 2024 season went on to challenge many of the UK’s winter crops, with frequent wet conditions subduing yields.

Despite very low disease levels, average fungicide treated yields were pegged at 11.8 t/ha in the harvest 2024 trial.

Note: For other nutrients, the RL protocols are even less prescriptive, stating: “… provide adequate phosphorus (P), potassium (K) and sulphur (S), taking into account local circumstances”. They say nothing about micronutrients.

Harvest 2025

In 2025, the trial site hosts one of five winter wheat trials managed to a bread-making specification, which adds an additional twist to nutrient management.

In such trials, we apply extra nitrogen to target 13% grain protein content: 80 kg/ha of granular nitrogen at growth stage 37 or foliar urea up to growth stage 73.

At the end of February, the plots looked very green, with the first nitrogen dressing imminent (we have applied nitrogen as early as 8 January in some years at this site).  

Other nutrients will be applied soon, including sulphur and magnesium, as well as micronutrients at regular intervals.

Reducing nitrogen

According to the British Survey of Fertiliser Practice, the average field rate of nitrogen for milling wheat in Great Britain is just under 200 kg/ha (2019–2023).

The high potential yields in the RL trials call for appropriately high nitrogen rates. However, many farmers cut nitrogen applications below RB209 recommendations to reduce input costs.

During the RL review, we received requests to provide more information about how varieties perform under reduced-nitrogen situations.

Plant breeders state that reducing nitrogen rates simply lowers yield across the board and does not affect the rank order of varieties greatly. It was a view confirmed by an AHDB-funded review of the literature (by NIAB and ADAS) in 2024.

Any reduction in nitrogen needs to be carefully considered. For example, the AHDB Cereal Quality Survey results often show that many UKFM Group 1 commercial samples fail to hit grain protein specifications. A lack of nitrogen available to the crop is often likely to be the cause.

A key debate is how to measure nitrogen use efficiency (NUE) and track traits through the variety pipeline – from plant breeder selection of lines to variety trials (including the GB and NI Variety Lists) – to improve varietal performance.

Although switching variety is unlikely to improve NUE, switching fertiliser products might.

Our Strategic Cereal Farms are comparing traditional soil applied nitrogen with foliar applied nitrogen (see page 24 in the winter 2024 edition of Arable Focus magazine).

Further information