Post-heatwave nutrition advice for autumn crop success

Informed nutrition decisions this autumn will be critical to establishing crops and strengthening resilience across arable systems, following the summer heatwave.

Maximising every kilogram of nitrogen applied will require strong crop emergence and a well-rounded nutrition programme.

See also: Later-drilled oilseed rape requires tailored agronomy

“Setting crops up properly to receive that first application of spring nitrogen as efficiently as possible is so important,” says Agrii national fertiliser manager Tom Land.

“Much of this comes down to creating optimum root structure and mass to ensure full use of every kg of N,” he stresses.

Larger, early N dose advised

With growers likely in for a wet autumn and winter following the prolonged dry summer, conditions could soon get challenging.

Tom is advising larger doses of up to 80kg/ha N in the first fertiliser application window to build biomass both above and below ground.

“We are seeing milder autumns followed by a wet January and February, with late frosts followed by a dry period.

“This results in a shorter timeframe for cereal crops to take up and utilise N fertiliser,” he says.

Cereals require about 160kg/ha N to build a canopy sufficient of delivering a basic yield. However, growers should always consider residual N.

“Late applications of fertiliser to dry soils will reduce N uptake as fertiliser cannot be moved into the rooting zone.

“Some fertilisers will be lost to volatilisation. Obviously, it’s important to avoid waterlogged soils as well,” says Tom.

He recommends 80kg/ha N for winter wheat in the first dose. “Winter barley responds to early N protecting tiller numbers so consider splitting your total N requirement in half and applying 50% pre GS30 and the balance pre GS32.”

Crops like oilseed rape can move quickly into the spring and you only get time for a couple of applications.

A key benefit of this year’s early harvest is growers now have ample time to focus on setting up seed-beds and building the foundation for solid crop performance.

Tom discusses four key areas that growers can focus on this autumn to help achieve optimum production at harvest 2027 and build greater resilience longer term.

1. Focus on a soil pH of 7

Maintaining soil pH at the correct level of pH 7 is key to supporting optimum nutrient availability, long-term soil health and importantly, financial resilience.

“It’s definitely an area that it is too frequently overlooked, but it’s essential to get this right. Autumn is the best time to take action,” says Tom.

The earlier harvest is giving grower’s a great opportunity to get soil pH tested and get lime on the land where it is needed.

An overly acidic soil can see between 16% and 51% of applied fertiliser not taken up by the plant, with significantly reduced nitrogen use efficiency (NUE).

“At current costs, this translates to a cost of £117-£267/ha of unutilised fertiliser based on 190kg N/ha, 55kg P/ha, 85kg K/ha at August 2026 pricing.”

As well as benefiting from improved NUE and yields, there are other advantages to be gained from maintaining the correct soil pH.

“For a start, it prevents acid-favouring weeds taking hold, but it also helps with disease prevention, inhibits transposition and movement of heavy metals that can lock up key nutrients and increases soil microbial activity.

“It’s important to give liming and soil pH the same level of attention and accuracy as the rest of the nutrient planning process.”

2. Make full use of phosphate

Adequate phosphate (P) uptake is essential to crop establishment and all-important root mass. The autumn period is the perfect time to address this.

While UK soils contain substantial reserves of phosphorus, only a small proportion is readily available to crops.

This makes managing soil conditions and P availability important when establishing crops following a challenging summer.

“It’s not just about making the correct applications. Getting soil phosphate mobilised and absorbed by crops is important,” says Tom.

Soils over chalk or limestone have high levels of calcium, which increases soil pH and locks up phosphate.

A soil phosphorus activator can help unlock P and improve nutrient availability. Agrii’s soil applied Agrii-Start Release works on calcium, aluminium and iron cations to displace locked-up phosphate.

According to Agrii R&D, the approach can release 40kg/ha of locked-up phosphate from the soil, reducing fertiliser expenditure and increasing winter wheat yields by as much as 1t/ha.

“In two years of trials with wheat set at a price of £180/t, the improvements in margin range from around £60/ha to more than £120/ha giving a return on investment of £36/ha to £81/ha.

“Don’t forget the saving made on applied fertilisers and the environmental gains by ensuring P is taken up by crops.”

3. Protect against stress using zinc, potassium and magnesium

Nutrients such as zinc, potassium and magnesium play an important role protecting crops against the effects of stress, particularly drought and heat. 

• Potassium (K) helps regulate water balance and stomatal function, supporting water-use efficiency and helping crops maintain turgor during drought and heat stress.
• Magnesium (Mg) is essential for chlorophyll, photosynthesis and energy production, helping crops maintain photosynthetic activity during periods of stress.
• Zinc (Zn) supports antioxidant defence, root development and stress-response mechanisms, helping protect cells from the oxidative damage associated with drought and heat.

Understanding the plant’s nutritional requirements when water is in short supply and air temperatures are more than 35C can go a long way to helping them survive prolonged periods of stress, he explains.

“Timely use of these nutrients is something we are going to have to build more into future fertiliser plans,” says Tom.

Newly developed roots during seed germination contain up to 200ppm of zinc, which indicates the important role of this nutrient. For example, during early seed germination and seedling development.

“Mg and K are essential in the maintenance of photosynthetic carbon dioxide fixation and transportation of assimilates and key nutrients in chloroplasts with wheat plants enduring low Mg supply, in particular, being especially susceptible to heat stress.

“Wheat plants in drought situations with an adequate supply of K use approximately 12 times more carbon dioxide, a strong indication of the rate of photosynthesis taking place, than those with inadequate levels.”

Combining K with N in a balanced nutrition approach has been proven to significantly increase NUE and yields through a synergetic approach, he adds.

Results from the International Potash Institute show when N and K are applied separately, each element can produce a yield response of 2t/ha in wheat, but when combined this rises to 5t/ha.

“Potassium improves NUE by enabling better N uptake and utilisation with multiple experiments showing a typical K application of between 30-150kg K20/ha results in improved NUE of 10-40%.”

4. Embrace new technology and thinking

Fertiliser use is a major on-farm cost and one of the main contributors to the carbon footprint of production. Efficient use is essential.

“Routine soil testing is becoming widely adopted, but soil mapping and production of detailed nutrient plans are areas where new technology can really help boost input efficiency,” says Tom.

“Technology is moving quickly in crop nutrition – not just in terms of product development but with regard to support services to plan and monitor nutrient usage in cost-effective ways.”