Agronomy Exchange: YEN data review shows crop limitations

Before Adas crop physiology consultant Dr Thomas Wilkinson addressed the question of where yield is won or lost, he posed the question to Agronomy Exchange delegates of whether maximising yield is still relevant.

With low grain prices and high input costs, it is a question many growers have probably asked themselves several times. Fortunately, with a data set of 3,000 entries generated over the past 14 years – and 1,000 covering winter wheat – the Yield Enhancement Network (YEN) is an extensive resource to base decisions on.

And the evidence is clear. “There is a strong relationship between yield and gross margin,” Thomas told delegates. And that might be no bad thing in the drive to reach net zero. Higher crop investment doesn’t necessarily mean that an increase in yield directly correlates with an increase in carbon dioxide emissions.

He explained that for those whose input costs equated to £450/ha, the data reveals a crop of 3t/ha will cover variable costs, while it is 5t/ha for those who invested more (£800/ha). Although the YEN data doesn’t include fixed costs, it is a guide to how crops might be managed in the future, he explained.

Over the course of the YEN cereals programme, an 8t/ha wheat crop delivered a margin of £800/ha, while a 12t/ha crop achieved £1,400/ha.

Looking ahead

More important is how the data can help growers in the future. Defra data shows the UK average for the 2024-25 season was just 7.2t/ha, with many blaming the warm, dry spring, and Thomas revealed some fascinating insights.

Certainly, the changing climate has affected cereal growing. Meteorological data collected over 10 years as part of the YEN programme shows that the temperature from October to July has increased by 0.5C, and June and July  is 0.8C warmer.

The question is how that has affected crops. By growth stage (GS) 61, the data is relatively stable, with wheat hitting this key stage typically a day – or on occasions two – earlier than they did in the past. Thomas explained that this isn’t a great surprise, as it is genetically determined and related to day length.

But for GS87, GS92 and harvest it can now be several days earlier. “Warmer winters have been good for yield, but warmer summers not. Our figures suggest a 0.20t/ha gain due to better crop foundation between sowing and the start of stem extension. However, there has been a 0.26t/ha deficit due to grain-fill being compressed. This is offsetting genetic and agronomic advances,” he explained.

Hopefully, genetics might offer some hope. A focus for future varieties could be flowering earlier while maintaining current maturity dates,  thereby extending grain-fill.

Sink capacity a significant factor last season

Velcourt’s 2025 data shows yield was largely determined by ears/sq m, not by how well the grain filled. Technical director Nick Anderson points out that all crops had the same spring. What made the difference between a 7t/ha or 10t/ha crop was establishment. The damage wasn’t down to the dry conditions, but rather the autumn when the crop was set up.

© Tim Scrivener

The crops that performed best were the ones drilled in September, which got Nick and his team thinking about drilling practices. What Velcourt has to weigh up is where the risk lies. Is the greater risk a slightly heavier grassweed burden or establishing a later-drilled crop?

Yield-limiting factors

Until this becomes a reality, the question remains what growers can do. The data suggests sink capacity has been the key cause of yield loss over the period. But wheat yield is co-limited, Thomas pointed out.

With both sink and source factors possibly contributing to yield loss, and increased seasonal variability occurring, he advised delegates to conduct a post-mortem of crop performance. Combining grain nutrient and yield breakdown into smaller yield components, such as ear numbers, allows growers to evaluate where yield was lost. “Crops develop sequentially, therefore so does yield. Working backwards will allow growers to assess where conditions have compromised potential,” he explained.

The logic in doing that is validated in the YEN data. Drawing on the 60 highest-yielding crops – those over 14t/ha – and comparing them to average YEN entries found several similarities.

Winning YEN entry evaluation

Although he pointed out there is no guarantee of a 15t/ha wheat crop, he said what separated the top YEN entries from the rest was not just a high number of ears, but also more grains per ear and high thousand seed weight.

Reviewing high-yielding entries revealed that growers had optimised the rotation, with better yields coming from wheat following an effective break crop, typically OSR or a pulse. The use of organic manures also boosted yield, and he advocated effective disease control and plant growth regulator strategies.

Narrow rows improved tillering, and ear numbers correlate to both the amount of phosphorus applied and that found in the soil, as well as adequate access to nitrogen and sulphur. “The ideal is to keep crops green as long as possible to increase the duration of grain-fill,” he added.

OSR data

What separates OSR yields is seed setting. The data reveals that to get a 5t/ha yield, the crop needs to achieve 100,000 seeds/sq m. “YEN results show that the OSR is mainly sink limited. It’s not just a larger crop, it’s about canopy efficiency too.”

Achieving this involves good canopy management principles, he explained. The data revealed that crops with higher seeds/sq m were achieving a higher rate of seeds set per pod. “We know from previous work that there is an optimum number of pods to be set in OSR.

Targeting the optimum canopy green area index [GAI] of 3.5-4 at flowering helps get this balance right. It’s important to ensure the canopy can intercept the maximum amount of light, but not shade itself, and set the most seeds.”

To calculate seed set/sq m, Thomas suggested growers divide yield by thousand seed weight. Going back to the data, he explained that growers who had reduced seed rate to achieve spaced plants with more branches are likely to be more successful in hitting the 3.5-4 GAI target.

Thomas was joined by Velcourt technical director Nick Anderson. Velcourt has used the YEN programme as part of its aim to better understand where yield is won and lost, combining YEN results with its own crop performance data.

Presenting aggregated seed number versus seed weight from two years of Velcourt YEN entries, Nick alerted delegates to two areas of the chart – crops with high grain number but low grain weight (source-limited) and the opposite, low grain number but high grain weight (sink-limited).

What was quickly evident was that the majority of Velcourt’s poorer-performing crops were sink-limited. That might not have surprised everyone in the audience, but the difference might.

“The mean difference between source-limited and sink-limited crops is close to 1t/ha, at 9.7t/ha and 10.4t/ha, respectively,” he explained. “Our predominant issue is sink limitation and it is clearly costing us yield.”

What is interesting over that time is that much of Velcourt’s research has been centred around source-related issues. “Our focus has been on keeping crops green for as long as possible to prolong photosynthesis. I expect this reflects what many others have been doing too,” he added.

No doubt the focus of Velcourt trials will shift, but there are limitations to what can be done. Nick noted the management change that has taken place in quite a short period of time. He pointed out the move from planting slow-developing varieties like Claire in early September to fast-growing varieties such as Extase in late October. “I’m not sure as an industry we have fully compensated for this,” he added.