Nitrogen is one of the most important macronutrients for crop growth, yet one of the most challenging to manage.

Its highly dynamic nature makes it prone to losses through processes like volatilisation and nutrient leaching. This can often result in inefficient nutrient uptake for growers.

With Nitrogen Vulnerable Zone (NVZ) closed periods in full swing across the UK, now is a good time for farmers to think about planning ahead for spring fertiliser applications.

Regular soil testing provides the data essential to creating a strategic nutrient plan to optimise nitrogen use efficiency (NUE).

What soil test results can reveal for farmers

To optimise nutrient levels and maximise crop yields, it’s vital to determine the specific nutrient composition and pH of your soil to tailor your fertiliser applications – this is where soil testing comes in.

Here are the main nutrients to measure and analyse for cereal crops:

• Macronutrients: nitrogen, phosphorus and potassium – these are vital for plant growth.
• Secondary nutrients: calcium, magnesium and sulphur which help perform processes like photosynthesis and cell wall development.
• Micronutrients: iron, manganese, zinc and copper, required in small amounts to aid physiological processes.
• Organic matter: the optimal level is between 3-6% although this differs depending on soil type, weather and crop.
• pH: the optimum pH for most crops is between 6.0 – 7.0, encouraging plant growth and nutrient availability.

For more on how these factors affect soil, read our recent blog on soil nutrient supply.

Advice for farmers: When to conduct soil tests

Regulations set out by DEFRA in 2018, known as ‘Farming Rules for Water’ (FRfW), require soil tests to be carried out on cultivated land to monitor pH and soil nutrient status every five years.

AHDB also recommend conducting checks on soil structure and taking earthworm counts once or twice a year – compact soil can be hard for roots to penetrate, limiting access to water and nutrients while lighter soils struggle to retain nutrients, especially after increased rainfall.

Tests should be done at the same time each year to maximise comparability. The recommended time is during spring or autumn when the soil is subject to less extreme weather patterns.

Arable farmer and agronomist, Will Oliver says: “We soil test once a year and use a handheld nitrogen tester in between to monitor nitrogen levels of wheat and rape as they grow.

“A lush crop may need more nitrogen than a backwards crops, so it’s important to be able to check,” he says.

The data collected allows for tailored nutrient plans to rectify any imbalances.

Ensuring optimal nutrient quantities are applied not only reduces the risk of environmental consequences like leaching, but optimises NUE to maximise crop yields.

Tools available for soil testing

To comply with FRfW regulations, at least one test in a five year period must be accredited under the Monitoring Certification Scheme (MCERTS) to monitor pH and nutrient levels.

These tests can be carried out by an accredited agronomist or laboratory and must be submitted to the environment agency.

For more options that provide instant results, there are a range of handheld tools available to test for nitrogen levels.

Calculating nitrogen use efficiency (NUE)

To deliver the essential nutrients needed in the right quantities, you not only need to understand soil composition but also how efficiently crops are using the nutrients applied.

NUE measures the ratio of nitrogen utilised by a crop versus the total amount applied via fertilisers or organic matter.

Independent crop advisor, Allison Gundy says farmers should be aiming for NUE between 70-80%.

Higher scores run the risk of soil-mining, depleting mineral nitrogen levels in the soil, while lower scores signal a surplus, often leading to leaching and surface run off, effecting water quality.

In order to calculate your NUE, first work out your nitrogen output by multiplying grain yield by grain nitrogen percentage, Then divide this number by nitrogen input to produce your NUE percentage.

Planning ahead for optimal fertiliser application

Soil testing and calculating NUE go hand-in-hand, providing a clear picture of the nutrient composition beneath the surface, enabling farmers to make more informed decisions about specific nutrient applications.

By having an informed nutrient plan in place ahead of time, you can also streamline the fertiliser ordering process, ensuring you’re ready as soon as NVZ restrictions are lifted in spring.

Ultimately, a well-planned nutrient management strategy, based on accurate data, is the key to unlocking your crop’s full NUE potential.

For more on optimising nutrient use, read our blog on precise fertilisation.