Nitrogen management for milling quality in wheat

A relatively high grain protein content is required for bread-making flours. Find out how careful variety choice and nitrogen management will help you secure milling wheat premiums.

The UK milling industry uses about 4m tonnes of home-grown quality wheat in a typical year, according to UK Flour Millers (UKFM).

To grow for this market, close management of nitrogen (N) is required, as it is needed for the synthesis of grain protein, which is a major component of milling wheat quality.

As a result, additional nitrogen (above what is needed for economically optimum yield) is generally worthwhile.

Protein concentration (and quality) determines end-use suitability. It is highly dependent on variety, although weather, soil type and crop management are also influential.

In the AHDB Recommended Lists for cereals and oilseeds (RL), bread- and biscuit-making varieties are categorised into three groups based on the results of quality tests (commissioned by UKFM).

UKFM Group 1 (13% protein): bread-making varieties that demonstrate consistent milling and baking performance, which make up most of millers’ requirements (and command the highest premiums).

UKFM Group 2 (12.5% protein): varieties with bread-making potential but are not suitable to all baking systems.

UKFM Group 3 (11.5% protein): varieties with unique grain protein quality, which is needed to produce a range of flour types and products, such as biscuits and cakes.

Notes:

• Talk with local millers about their preferences before committing to a variety
• Some Group 4 soft wheats may also have a specific use in some flours
• Typical protein contents cited above

In the RL, nitrogen applications are guided by the AHDB Nutrient Management Guide (RB209). For most winter wheat trials, nitrogen rates aim to maximise the yields of feed varieties.

Some trials are grown to a milling specification, where extra nitrogen is applied to target 13% protein content. These trials are located on sites that have a good record of producing bread-making grain to a high specification. Varieties are grown as a first wheat.

The extra nitrogen is also applied in line with RB209 guidance – a granular fertiliser product applied to the soil during stem extension (about growth stage 37) and/or a liquid foliar spray applied at GS73.

Results are published in the "Protein content (%) – milling spec" line in the winter wheat table, which can guide how varieties perform in commercial situations when grown to a milling wheat input programme.

According to RB209, any decision to apply extra nitrogen should:

1. Follow RB209 recommendations for fertilising adequately for yield (all nutrients*).
2. Estimate the economic premium for meeting the protein specification (to determine break-even ratios).
3. Consider the farm’s past success in meeting grain quality specifications (not just protein**).
4. Estimate the uptake of previously applied nitrogen (especially in a low-spring-rainfall season).

*Because of the critical role of nitrogen in milling wheat, consider following RB209’s Measurement Method, especially when soil nitrogen supply (SNS) is likely to be large or uncertain. It is more accurate than the Field Assessment Method because it:

• Uses results of laboratory analyses to indicate soil mineral nitrogen (SMN) levels
• Accounts for crop uptake of nitrogen
• Estimates nitrogen mineralisation from organic matter after soil sampling

**In addition to protein, milling wheat premiums are paid according to moisture, specific weight, Hagberg Falling Number and admixture criteria.

Nitrogen fertiliser manufacture is energy-intensive and costly. This was particularly evident in 2022, which saw spikes in fertiliser prices and AHDB issue revised nitrogen guidance.

Nitrogen prices affect break-even price ratios. Higher prices decrease the optimal nitrogen application rates for feed wheat and increase the relative investment required to secure milling premiums.

Relatively small premiums may mean that the risk of applying extra nitrogen is not worthwhile, especially where a farm’s historic success in meeting the milling specification is poor and the cost of nitrogen is relatively high.

The pressure to reduce input costs and environmental concerns have underpinned a general reduction in the amount of nitrogen applied to milling wheat.

The difference in the average nitrogen rate for GB milling wheats halved (compared to non-milling wheats) between 2010 (34 kg/ha) and 2023 (17 kg/ha).

Table 1. Average field rates (kg/ha) of nitrogen for wheat in Great Britain (2019–2023)

Source: British Survey of Fertiliser practice

RB209 provides guidance on the rates and main application timings (including splits), which are influenced by the total nitrogen requirement and crop development.

Most of the main nitrogen applications are applied by the first stages of stem extension, about early May (starts at GS30). Urea fertilisers tend be applied relatively early to provide sufficient time for nitrogen mineralisation.

Although grain protein forms later, it mainly uses nitrogen redistributed from stems, leaves and roots. Relatively little grain nitrogen comes from uptake after flowering.

As a result, applications at the main timing need to ensure sufficient nitrogen is available for grain protein development.

Adjustments can be made based on typical grain protein contents achieved on the farm. RB209 states that grain protein is typically about 12% (2.1% N) for bread-making wheat and 11% (1.9% N) for feed wheat at the economic optimum rate of nitrogen for yield (for standard crop yields of 8t/ha).

If results are consistently above or below these values (over several years), RB209 recommends that adjustments are made to main nitrogen rates by 25 kg N/ha (up or down) per 0.5% difference in grain protein (30 kg N/ha per 0.1% difference in grain %N).

Conversions

The weight of grain protein relates directly to the weight of nitrogen, with a ratio of 5.7 to 1:

• Divide %protein by 5.7 to calculate grain %N
• Multiple grain %N by 5.7 to calculate %protein

Both nitrogen and protein are reported on a 100% dry matter basis.

Late nitrogen can help boost grain protein and promote canopy survival during grain filling.

RB209 states that typically:

• An extra 40 kg N/ha could increase grain protein by up to 0.5%
• An extra 80 kg N/ha could increase grain protein by up to 1%

Notes:

• Ensure that nitrogen rates comply with all relevant rules and regulations
• Always consider your local conditions and consult a FACTS Qualified Adviser if necessary

Applied to the soil

Most late nitrogen applications to the soil are made during stem extension (usually, GS32 to GS39).

When conditions are dry, nutrient uptake can reduce significantly. This is why applications to the soil after GS39 are not recommended (although they can still boost protein when weather is favourable). If soils are drying and/or no rainfall is forecast, then early applications are recommended.

Applied as a foliar spray

Rapid grain filling starts at GS71 and ends at about GS87, even when green tissues remain.

Generally, foliar urea sprays (usually applied about GS73) are better at increasing grain protein at very late growth stages, although no yield increases should be expected.

AHDB-funded trials show the application of foliar urea has no detrimental impact on baking quality (compared to soil-applied nitrogen).

The annual AHDB Cereal Quality Survey shows the challenge of hitting milling specifications.

For example, in the 2024 survey, only 31% (sample size of 845) of the milling wheat samples achieved the 13% protein target, with a wet growing season (which affected crop growth, nitrogen applications and nutrient leaching) contributing to the lacklustre protein performance.

Additionally, only about 40% of milling wheats entered in the ADAS Yield Enhancement Network (2013–2020) achieved more than 13% protein.

Attention to detail is the key to success, which can include considering the results of soil and grain analyses. The latter can indicate how much nitrogen was captured and used by the crop.

The results can help identify productivity constraints and guide fertliliser applications in subsequent seasons.

Notes:

• The relatively high yields associated with first wheats can dilute protein content
• Some factors that reduce yield raise protein concentrations (providing they do not affect nitrogen transport to grain)

RB209 states that an extra 40 kg N/ha could typically increase grain protein by up to 1%.

Application of this additional nitrogen during stem extension may give a small yield increase, as well as an increase in grain protein.

Application as a foliar urea spray during, but not later than, the milky ripe stage will result in a larger increase in grain protein content but cannot be expected to increase yield.