High YEN performance is rarely about a single decision, but a system that delivers year after year. In a drought-hit season, one Oxfordshire grower showed how variety, biomass and rooting combined to exceed potential, CPM finds out more.
“One thing YEN shows is that it’s often the same people near the top. It’s just doing everything a little better.” DAVID PASSMORE
By Charlotte Cunningham
There’s a consistent theme running through the YEN – while seasons vary, systems tend not to. Year after year, the same growers feature near the top – not because they’ve found a silver bullet, but because they’ve built a repeatable approach for maximum potential.
In 2025, that pattern continued. Oxfordshire grower David Passmore took top spot with a crop of KWS Zealum, delivering 14.3t/ha – a standout result in a season defined by prolonged spring drought and below-average national yields.
But while the headline figure is impressive, the real value lies in understanding how that yield was built – and, importantly, protected – through a combination of variety choice, system design and attention to detail across every stage of the season.
According to KWS agroservice manager Matt Bull, the performance of Zealum in this situation is no accident. “Zealum is a soft Group 4 feed wheat and a variety that fits particularly well where you’re drilling relatively early so looking to build biomass to secure higher grain yield,” he explains. “It develops steadily, has good disease resistance and, importantly for 2025, was able to hold on to green leaf area and keep building yield.”
Farming 365ha near Wallingford, David operates a mixed enterprise that integrates combinable crops with livestock. He says the rotation is central to the system, typically including a three-year grass ley followed by wheat, oilseed rape, wheat, peas, wheat and spring barley before returning to grass.
MAKING GAINS
It’s a structure that delivers multiple agronomic benefits, not least in terms of soil condition and weed control. “We have livestock, grass in the rotation and root crops,” he explains. “That means we have almost no blackgrass, so don’t have to delay drilling.”
That flexibility is significant because it means that where many growers are forced into later drilling to manage grassweeds, David can prioritise establishment conditions – typically targeting the end of September and early October.
The soils themselves are described as Andover series – flinty, chalk-based loams that are relatively easy working but inherently free-draining. On paper they might appear limiting, particularly in dry seasons, but in practice, long-term management has fundamentally changed how they function. “We’ve farmed here for nearly 70 years with grass in the rotation,” he says. “You have all those old root channels going down into the chalk.”
That legacy effect, built over decades, underpins one of the most important components of yield in this system – rooting depth.
Equally, at the core of David’s approach is a simple but critical principle – high yields require high biomass. “If you want 14t/ha of grain, you require more than 20t/ha of grain and straw,” he says. “You can’t get high yields without a big crop.”
This thinking aligns closely with YEN analysis, which consistently shows a strong relationship between biomass and yield. In 2025, David’s crop produced 21.5t/ha of above-ground biomass – placing it firmly in the high-performing category.
However, biomass alone isn’t enough – it must be efficiently converted into grain, reflected in harvest index. In this case, the crop combined high biomass with a strong harvest index of 57%, enabling it to deliver both yield and efficiency.
This balance is particularly important in challenging seasons, notes David. The 2024-25 growing year was characterised by one of the driest springs on record, with water stress limiting growth and reducing yields across much of the UK.
Despite this, David’s crop achieved 117% of its estimated yield potential – indicating not only strong resource capture, but also exceptional efficiency in converting those resources into grain.
Then, while system sets the direction, variety choice defines the framework for that system to operate. This year’s winning variety – Zealum – brings a combination of traits that align closely with David’s approach. It’s well suited to early drilling, has good disease resistance and a slightly later maturity – all of which contribute to its ability to build and maintain canopy. “It doesn’t get too lush, but it still builds a big crop and stands,” says David.
From a physiological perspective, Zealum’s slightly later maturity is significant. In 2025, later-maturing varieties tended to outperform earlier types, likely due to their ability to extend canopy duration and maintain grain filling under drought stress.
“That was a clear trend last season,” highlights Matt. “Broady speaking, later-maturing varieties generally performed above their long-term averages, and Zealum was one of those – it was around 1.8% ahead of its five-year mean.”
Zealum also has strong physical characteristics, producing large ears with high grain site potential – an important factor in driving final yield “Big, well-filled ears with lots of grain sites gives it that high yield ceiling if managed correctly,” adds Matt.
Establishment is the first major opportunity to influence yield, and in David’s system, drilling timing is non-negotiable. “We’re aiming for the last few days of September and the first few days of October,” he explains. “So not particularly early, but definitely not later sown.”
The YEN data supports this approach. Across multiple years, delayed drilling has been associated with yield penalties of around 0.7t/ha per month, reflecting reduced biomass accumulation and shorter growing seasons.
In David’s case, Zealum was drilled on 5 October at 325 seeds/m² – a rate driven partly by seed production requirements but also ensuring a robust plant population. While the variety has good tillering capacity, David prefers to establish a strong base population, reducing reliance on tiller compensation later in the season.
Once established, the focus then shifts to building canopy through nutrition. The field received farmyard manure ahead of drilling – contributing to soil organic matter levels of 8.1% – followed by a nitrogen programme based entirely on urea. Total nitrogen applied was approximately 231kgN/ha delivered in four splits. “We try to get most of it on before the end of March,” says David. “If you hit a dry spell later, you can struggle to get it into the crop.”
Matt believes this early nutrition strategy is central to the crop’s performance. “What David’s done well is build biomass early and then retain it,” he comments. “That combination of early drilling and getting nutrition on at the right time in combination with thermal time, is what drives tiller production survival and ultimately grain number.”
This strategy proved particularly important in 2025, when the dry spring limited nutrient uptake in many crops and contributed to reduced tiller survival and ear numbers. Even in this case, analysis suggests nitrogen supply may have been slightly limiting. The crop took up 286kgN/ha while estimated requirement was closer to 303kgN/ha, explains David.
But with high biomass comes increased risk, particularly in terms of lodging. David addresses this through a proactive PGR strategy, applying three treatments through the season. “Even stiff varieties will lodge if you don’t manage them,” he notes.
“If you’re pushing crops hard, particularly with nitrogen and early drilling, then managing that canopy becomes critical,” adds Matt. “It’s about supporting that biomass so it can translate into yield.”
The little and often approach that David took is arguably spot-on for high potential crops, avoiding stressing the crop and helping to mitigate risk if weather compromises any of the timings.
Beyond lodging control, PGRs also play a role in root development. Early applications can enhance root growth, improving the crop’s ability to access water and nutrients – a key advantage in dry conditions. YEN data supports this strategy, showing an average yield increase of 0.8t/ha per PGR application.
If biomass is the engine of yield, then rooting is the fuel supply. YEN analysis estimated that David’s crop captured 165% of available water – suggesting access to water beyond what was initially assumed based on soil description.
This aligns with observations that high-yielding crops often require rooting depths exceeding 1.5m to access sufficient moisture. In this instance, the combination of chalk subsoil and long-term grass rotation appears to have created an effective reservoir. “If you dig down into the chalk in a dry summer, it’s cool and moist,” raises David. “It’s like sitting on a sponge.”
ADAS crop physiologist, Dr Pete Berry, confirms this hypothesis. “One of the key secrets to success was deep rooting, which meant the crop didn’t run out of water prematurely and was able to continue performing all the way through June and July,” he comments.
Matt notes that Zealum appears well-suited to these situations. “We’ve seen it perform particularly well on lighter soils where water can be limiting. It’s able to hold onto green leaf area and keep going when conditions get tough,” he says.
However, yield is ultimately determined by its components, and in this crop, both grain number and weight were strong. Grain numbers reached 27,000/m², supported by ear populations of 495 ears/m² and an average of 53 grains/ear. Grain weight was also high, with a thousand grain weight of 53.1g. These figures suggest a crop that not only built yield potential early, but maintained it through to harvest.
This was facilitated by extended canopy duration. The crop flowered on 31 May and reached full senescence on 4 August – providing a long grain-filling period despite the challenging conditions.
Equally, despite relatively low septoria pressure in 2025 and good inherent disease resistance within Zealum, disease management remained robust. The crop received a full fungicide programme, including T1 and T2 applications, with a T3 to protect grain quality, reflecting a mindset focused on protecting yield potential rather than reacting to visible disease.
TANGIBLE UPLIFTS
YEN analysis shows that fungicide applications are associated with yield increases of around 0.6t/ha per application – reinforcing the importance of maintaining canopy health.
While the technical components are clear, David is quick to point out that success isn’t about any single factor. “One thing YEN shows is that it’s often the same people near the top,” he says. “It’s just doing everything a little bit better.”
That includes seedbed preparation, drilling timing, nutrition, crop protection and ongoing management. “You never look at a crop and think it’s perfect,” he adds. “You’re always thinking what could you do better next year.”
Looking ahead, for David the focus remains on refining the system further. “You’re always hoping for that perfect year, but the reality is you have to be set up to take advantage of it if and when it comes.”
And as YEN continues to demonstrate, high yields aren’t confined to specific regions or soil types. With the right approach, they are achievable almost anywhere. As proven, a combination of variety selection, deep rooting, sustained canopy and carefully managed inputs have allowed a crop on chalk soils in Oxfordshire to outperform not only its peers, but its own estimated potential.
This article was taken from the latest issue of CPM. Read the article in full here.
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