Soil testing – the tools available to UK farmers

With NVZ closed periods in place across the UK, now is the ideal window to get ahead with soil testing to identify the nutrient requirements of your soil.

This way, you’ll have reliable data at the ready to shape precise fertiliser plans well ahead of spring applications.

This not only contributes to better nitrogen use efficiency (NUE), more resilient crops and increased yields, but also allows for ordering fertiliser ahead of time to get prepared.

The importance of soil testing

Improving NUE and maximising yields hinges on having a clear understanding of the nutrients already present in the ground.

Regular soil testing provides accurate data on pH, structure and nutrient status. This information can help you to build accurate spring nutrient plans which target specific requirements and avoid under or over-application.

The risks of not getting the application right are:

• Over-applying fertiliser – this increases the risk of leaching where soluble nutrients are washed out of the soil by rainfall, negatively impacting watercourses.
• Under-applying fertiliser – this depletes existing nutrient stores and decreases soil fertility and crop productivity.

Maintaining a consistent soil testing schedule means year-on-year results are comparable, enabling you to track progress, identify patterns and fine-tune nutrient management. Read our recent blog to learn more about the importance of soil testing to improve NUE.

Traditional soil testing methods

All UK arable farmers are required by laws set out by Farming Rules for Water to carry out lab soil tests by, or with, their agronomist.

Cultivated land should be tested at least once every five years to inform nutrient planning, with measurements taken for soil pH and nutrients like phosphorus (P), potassium (K) and magnesium (Mg).

AHDB’s management guide is a useful source to help interpret soil test results accurately to influence a nutrient plan.

Your agronomist will take representative samples from across each field, up to 0-15cm below the surface, and send them to an accredited lab to be analysed.

Most farmers use agronomy services that sample and manage the lab submission for you, but you can also send samples yourself – AHDB maintains a current list of soil testing laboratories that you can send to, as well as companies that collect samples.

Portable soil testing kits

Once legally required tests are complete, there is a range of on-farm tools available for farmers to use between lab cycles to help track and fine-tune day-to-day decisions.

Here are some examples:

• Portable probes: These use electrical/optical sensors to measure saline levels, pH, temperature and some nutrients such as nitrogen, ammonium, potassium and phosphorus.
• Handheld nitrate meters: These use a small soil extract to give an instant nitrate reading; this is useful for tracking how levels move through winter into spring, although they are limited on depth of the test area compared to a full analysis.
• DIY colorimetric kits: These indicate levels of nitrogen, ammonium nitrate, potassium and pH instantly using a colour chart. These tests are useful for comparing zones but should be used as a guide, not as comprehensive data.
• Soil structure – spade test: Although this is not chemistry, it is vital for providing context on compaction, rooting depth and biological activity – all of which influence nutrient availability in the soil.

Used alongside your five-year accredited test, these tools are great for obtaining fast feedback leading up to spring, as well as monitoring crop growth later in the season, giving you the confidence that you’re optimising NUE when applications begin.

Emerging soil testing methods

Newer technology-led options are continuing to emerge, adding another layer of insight into soil nutrition and especially useful for larger blocks or tricky fields.

Here are a few examples:

• Drones / remote sensing: These indicate moisture, temperature, nutrient-stress proxies, and texture across an entire field quickly. LandScan UK specialise in remote sensing using photogrammetry and GIS augmentation.
• Ground-based proximal sensing: These include ATV, tractor, and handheld sensors for moisture, pH, texture and some nutrients with GPS logging. This method can cope with a high throughput but does require careful calibration. gprSense offers ground-penetrating radar and software solutions for soil and material characterisation, to map out the root zone.
• Satellite remote sensing: This offers farm-wide multispectral/thermal sensing for seasonal trends and sampling prioritisation. It offers huge coverage with low marginal cost. RSAC Ltd focus on converting satellite image processing into actionable information to influence soil nutrition.

To learn more about the different ways soil testing can affect soil nutrient supply and why it’s important, read our recent blog.