Heatwaves, drought and potash: what the 2026 season could mean for UK cropping in 2027

Author: Alli Arden

14th September 2026

NRM

Agriculture

The UK’s 2026 growing season provided an important illustration of how moisture limitation can influence nutrient-use efficiency and crop access to soil nutrient reserves. Although potassium is widely recognised for its role in drought resilience, the agronomic benefit of this nutrient depends not only on soil supply but also on its availability to the crop, and the relationship between drought and potash.

As discussed in our first blog, which you can read here, potassium is central to stomatal regulation, photosynthesis, assimilate translocation, enzyme activation and plant water relations. Under normal conditions, crops depend on soil water to move potassium to roots for absorption. Drought reduces potassium mobility, limits root exploration, and decreases crop utilisation of soil reserves. This highlights the difference between potassium availability and accessibility: a field may have enough potassium, but drought can cause deficiencies during key growth stages.

The prolonged dry conditions experienced across many regions during 2026 therefore raise several important agronomic questions:

• To what extent did drought and heat constrain potassium acquisition during critical growth stages?
• Did reduced rainfall prior to harvest increase potassium retention within straw residues and subsequent nutrient offtakes?
• What implications might this have for field potassium balances, nutrient recommendations and crop performance in 2027?

In this second blog, we explore the likely effects of the 2026 growing season on potassium dynamics within UK arable systems, examining the consequences for crop uptake, straw nutrient offtake, soil nutrient status and the management strategies that can help safeguard productivity in future seasons.

Drought and potash: why drought can restrict potassium uptake

The prolonged heat and drought experienced across many regions during 2026 are likely to have reduced potassium acquisition during periods of peak physiological demand. Fields with restricted rooting depth, soil structural limitations or lower water-holding capacity may have been particularly exposed. Importantly, reduced potassium availability can further impair stomatal regulation and water-use efficiency, potentially intensifying the effects of moisture stress.

Potassium has a fundamental role in stomatal function, regulating the balance between carbon dioxide assimilation and water loss. Where potassium supply becomes limiting, stomatal responsiveness may be impaired, reducing photosynthetic efficiency and biomass production while increasing susceptibility to drought stress.

Consequently, drought can restrict potassium uptake, and suboptimal potassium nutrition can further exacerbate the physiological impacts of drought, creating a negative feedback mechanism that constrains crop performance.

Could straw contain more potassium this year?

Consequently, drought can restrict potassium uptake, and suboptimal potassium nutrition can further exacerbate the physiological impacts of drought, creating a negative feedback mechanism that constrains crop performance.

One of the less frequently considered consequences of dry harvest conditions is their influence on potassium retention within crop residues.

PDA guidance indicates that rainfall between physiological maturity and baling can significantly reduce straw potassium concentrations through leaching. Conversely, prolonged dry conditions can result in a greater proportion of accumulated crop potassium being retained within standing straw.

As a result, straw removed following the 2026 season may have exported greater quantities of potassium than growers anticipated when compared with wetter years. This has direct financial implications. Every tonne of straw sold off the farm exports significant potassium that must eventually be replaced if soil fertility is to be maintained.

Illustrative sensitivity analysis for 5 t/ha wheat straw

Assuming muriate of potash (MOP) valued at £372/t (60% K₂O), the replacement cost of potassium is approximately £0.62 per kg K₂O.

Straw K₂O concentration based around the PDA average: ww/wb = 10kg, sw/sb = 13kg K₂O/t

This highlights the importance of viewing straw not simply as a by-product, but as a potentially significant potassium reservoir. Following particularly dry seasons such as 2026, reviewing straw nutrient content, estimated nutrient offtakes and field potassium balances may improve the accuracy of nutrient replacement programmes and soil fertility planning.  A business baling 300 ha of wheat straw, for example, could export an additional 6,000 kgs of K₂O, as concentrations increase from 10 to 14 kg K₂O/t, representing more than £3,720 of additional potassium value leaving the farm gate.

While there is limited research directly linking heat stress to potassium concentrations in cereal straw, prolonged periods of heat and drought do accelerate crop senescence and shorten grain filling. Potassium is largely retained in leaves, stems and straw rather than being incorporated into grain, so crops that mature prematurely may leave a greater proportion of their potassium in the vegetative material at harvest.

Drought-affected crops may have increased spatial variability in nutrient distribution across fields. Areas where root exploration and nutrient acquisition were restricted may exhibit localised potassium depletion despite satisfactory average soil analysis results, and areas where straw was removed may have elevated potassium exports relative to standard assumptions.

These factors can influence subsequent crop performance by affecting nutrient availability, root development, and stress resilience. Repeated drought events also expose underlying soil constraints, including compaction, shallow rooting depth and low organic matter status, all of which can reduce access to both water and nutrient reserves.

What should advisors and farmers look for?

As crops emerge this autumn and next spring, growers should pay attention to:

• Recent soil potassium indices
• Fields with repeated straw removal
• Variability in crop establishment
• Areas prone to drought stress
• Declining organic matter levels
• Returning crop residues where appropriate to enhance potassium recycling and support field nutrient balances

Ultimately, while climatic conditions cannot be controlled, the resilience of cropping systems can be strengthened through evidence-based soil and nutrient management. A soil test alone may not tell the entire story. Reviewing nutrient budgets and field-specific offtakes from the 2026 harvest will be equally important.

Drought and potash: using integrated nutrient management approaches

While weather cannot be controlled, farming systems can be adapted to improve nutrient use efficiency.

As climate variability increases, understanding the interactions among soil moisture, nutrient availability, and residue management will become increasingly important for evidence-based nutrient management. Businesses that incorporate field nutrient balances, crop offtakes and soil potassium status into strategic decision-making are likely to be better positioned to maintain productivity under increasingly variable climatic conditions.

The 2026 season reinforces an important agronomic principle: potassium nutrition is governed not only by the quantity of potassium present within the soil, but also by the crop’s ability to access and utilise that resource during periods of environmental stress.

Here’s what you can do to give your soils the best chance after a summer like this year’s:

• Strive to improve soil structure and rooting depth to enhance access to both water and nutrient reserves during dry periods.
• Increase soil organic matter (SOM) through organic amendments, cover crops and residue management to support moisture retention and nutrient cycling.
• Use integrated nutrient management strategies that combine fertiliser, manure and crop residue inputs based on field-specific nutrient balances.
• Use an accredited laboratory to get the accurate, reliable data you need to quantify potassium removal, assess soil nutrient status and develop robust, field-specific nutrient management strategies.

How NRM can help

As climate variability increases, understanding the interactions among soil moisture, nutrient availability, and straw management will become central to maintaining resilient and productive UK cropping systems. Advisors and farm businesses that treat potassium as a strategic resource will be best placed to withstand future drought challenges.

NRM offers a range of analytical services which can support decision-making. Regular soil testing for pH, phosphate, potash, magnesium, and nitrogen levels remains one of the most effective tools for improving crop performance and nutrient efficiency. If soils have not been analysed within the last four years, now is the time to act.

Now that the rains have started, contact your agronomist, advisor or soil sampling provider to arrange testing.

References

1. Nutrient Management Guide (RB209) 2026. Guidance on potassium indices, nutrient budgeting, soil analysis and nutrient replacement.
   • https://ahdb.org.uk/RB209
2. Grain Nutrient Analysis and its Role in Management. Highlights the interaction between soil supply, crop uptake, soil moisture and rooting constraints.
   • https://ahdb.org.uk/grain-nutrient-analysis-and-its-role-in-management

Potash Development Association (PDA). Nutrients in Crop Material. Evidence that straw commonly contains a substantial proportion of total crop potassium and notes that rainfall before baling can significantly reduce straw potassium content.

• https://www.pda.org.uk/pda_leaflets/nutrients-in-crop-material/the-pda-pk-nutrient-calculator/

Mengel & Kirkby et al. Potassium Availability in Relation to Soil Moisture. Demonstrates reductions in potassium mobility and plant uptake as soil water content declines.

• [link.springer.com]

Zhu et al. (2025). Applied Potassium Negates Osmotic Stress Impacts on Plant Physiological Processes. Meta-analysis showing the role of potassium in mitigating the impacts of drought and osmotic stress on crop performance.

• [academic.oup.com]

Zhang et al. (2021). Long-term Straw Returning Improves Soil K Balance and Potassium Supplying Ability. Evidence that residue retention improves soil potassium reserves and long-term nutrient resilience.

• [pmc.ncbi.nlm.nih.gov]