Dry spring 2025: Impact on crop nitrogen uptake

Spring has delivered extremely dry conditions across most of the UK. Emma Willis examines how a lack of soil moisture can impact nitrogen uptake in winter wheat.

What a difference a year makes! This time last year, we were hoping for some long, dry spells.

Our crop condition report (April 2024) stated that winter wheat was in “one of its poorest states in recent years” after crops had sat wet for weeks on end.

Fast-forward 12 months and we now have an extremely dry start to spring across most of the UK.

In fact, by the middle of May, the UK had recorded the driest and sunniest start to spring on record (and the warmest since 1960).

Most cereal and oilseed rape crops were in fair, good or excellent condition at the end of April, but some were showing the first signs of drought stress.

A fortnight later and many more crops are showing signs of stress. Some farmers, blessed with water sources and infrastructure, even started to irrigate some cereals.

In winter wheat, most nitrogen is taken up during the construction phase during April and May to support tillering and stem elongation. Naturally, most nutrients are applied before and during this phase.

For the fertiliser applied, some will be sitting, waiting patiently for moisture to work its magic. Recent showers will have provided some relief, especially to the stressed crops lucky enough to see them.

Moisture is needed to dissolve nutrients and move them to plant roots. However, it does much more.

For example, ammonium nitrate contains nitrogen in nitrate (NO₃⁻) and ammonium (NH₄⁺) forms. Although the former is immediately available for crop uptake, the latter needs moisture-loving microbes to convert them to nitrates (via nitrification).

For urea fertilisers, an extra moisture-requiring step is required. This is because urea first needs to be converted by urease enzymes (which are naturally present in soils) to ammonium forms.

Even liquid nitrogen fertilisers, which are solutions of urea and ammonium nitrate, are still hampered by a lack of soil moisture (which is still needed to convert nitrogen into crop-available forms).

If crops cannot absorb nitrogen, yields suffer and fertiliser investment is lost. It is a major economic risk.

Dry, sunny conditions also cause another fertiliser issue: leaf scorch, which reduces the photosynthetic area.

The Nutrient Management Guide (RB209) provides guidance on the rates and main application timings (including splits), which are influenced by the total nitrogen requirement and crop development.

Most of the main nitrogen applications are usually applied by the first stages of stem extension, about April (starts at GS30).

RB209 provides information on the yield impact of applying less than the optimum amount of nitrogen (see Table 4.33 in Section 4).

RB209 also states the key steps to decide whether to apply extra ‘late’ nitrogen to boost grain protein in milling wheat:

1. First follow recommendations for fertilising adequately for yield.
2. Consider the value of the economic premium for meeting the protein threshold.
3. Consider the farm’s past success in meeting the required grain quality specification.
4. Consider the uptake of previously applied nitrogen in a low spring rainfall season.

This year, the final point is in focus.

Although late applications can boost protein, they are less effective in dry soils.

Where soils have had a drink recently, it may still be worth making late nitrogen applications.

However, a close eye needs to be kept on the forecast, because soils will need to stay moist for effective nutrient conversion and crop uptake – with urea fertilisers needing the most time to work their magic.

This is why, ideally, all soil-applied nitrogen should be applied by GS39.

The current forecast (14 May 2025) suggests the dry and sunny condition will continue for most of the UK for several days, at least.

Of course, foliar urea applications are a potential option. Applied during the milky ripe stage (GS73), these are generally better at increasing grain protein than soil-applied nitrogen (but cannot be expected to increase yield).

Any long-term plan needs to improve soil health to provide a buffer against the increasingly unpredictable and extreme weather.

Main benefits of healthy soil

• Enhanced water retention: Healthy soils with high organic matter content retain more water, which reduces the impact of drought
• Improved soil structure: Good soil structure promotes better root growth and water infiltration, helping crops withstand both drought and heavy rainfall (such soils are also less prone to erosion from heavy rain and wind)
• Nutrient availability: Healthy soils support a diverse microbial ecosystem that enhances nutrient cycling, helping plants get the nutrients they need

For example, using cover crops, only moving soil when necessary and increasing organic applications can improve overall soil health.

As always, it is important to use in-season lessons to improve next year’s plan.

Tips for fertiliser planning next year

• Have a soil management plan: Use it to understand the health of your soil and how to improve it
• Conduct soil tests: Use the results to understand nutrient levels and adjust fertiliser applications accordingly (drought conditions can cause uneven nutrient distribution, so soil testing will quantify this impact)
• Produce a nutrient management plan: Use it to plan fertiliser types, amounts and timings for your crop and target yield
• Monitor crops: Inspect crops during the growing season and adjust plans, as necessary (e.g. timings in response to soil moisture)
• Precision agriculture: Adopt techniques to apply fertilisers more efficiently, helping to target areas that need it most
• Organic amendments: Aim to improve levels of soil organic matter (e.g. apply organic materials or incorporate straw or cover crops)