Getting to the root of grain protein prediction in milling wheat

Findings from field trials of a root-based grain protein predictor are available in a new research report. The results show that the test can be used to help decide whether to apply late nitrogen to milling wheat.

The ability to accurately predict grain protein content during relatively early growth stages would revolutionise nitrogen management in winter milling wheat.

It would help farmers judge whether their crops are likely to meet milling specifications for protein and adjust nitrogen applications accordingly.

The research, funded by AHDB and Hill Court Farm Research, analysed root samples for regulatory signals associated with nitrogen uptake.

The results were used to indicate the nitrogen status of the crop and provide a prediction of potential grain protein content.

The research capitalised on a related study investigating nitrogen and sulphur fertiliser management in winter wheat.

This work included ten identical replicated nitrogen-rate field trials in England and Scotland (2019–21).

The trials used three bread-making winter wheat varieties (Zyatt and Skyfall and Siskin) to test the effect of various nitrogen rates above those required for optimum yield (as indicated in RB209) – 0, 40, 80 and 120 kg/ha.

The extra nitrogen was applied at either GS 31 (early stem extension), GS 37 (late stem extension) or GS 70 (start of grain filling).

The researchers sampled roots at GS 32 (early stem extension), GS 39 (late stem extension) and GS 70 (milk development of the grain).

Root analysis gave a reasonable prediction of grain protein, providing roots were sampled between GS 39 and GS 70.

Optimal sample timings:

• Late May/early June for solid fertiliser application
• From the beginning of June for foliar fertiliser application

Suboptimal timings:

• During periods of drought
• Too soon after rain following drought
• Too soon after the main fertiliser application

The largest financial benefit was gained when the protein prediction was ≥13%, when 80% of samples achieved milling specification without applying nitrogen above that required for optimum yield.

This compared to only 50% of samples gaining a financial benefit when late nitrogen was applied regardless of the outcome of the test. In other words, 50% used fertiliser that was not required.

When the advice from the test was to apply fertiliser, only a small percentage (5%) achieved milling specification without extra nitrogen.

This research has delivered encouraging grain protein predictions from wheat root analyses and the test is commercially available.

However, it is unlikely that the approach will deliver perfect protein prediction, primarily because it is unable to account for all factors that affect final protein content, such as variation in photosynthesis.

Despite this, the results showed that this indicator is more sensitive and a better indicator of crop nitrogen status than other approaches, including measurements by chlorophyll meter (SPAD), near-infrared spectroscopy (NIRs) or leaf nitrogen content analysis.

With fertiliser prices high, any evidence that helps farmers match nitrogen applications to crop requirements would be welcome.

This research has provided a significant step forward in grain protein prediction and the ability to fine-tune nitrogen applications.