Soil testing before spring: optimising nitrogen and nutrients for higher yields
NRM
Agriculture
The days are starting to get longer, and spring 2026 is just around the corner. Now is the ideal time to step back and assess soil nutrient status to ensure crops get the best possible start. Whether you’re planning nitrogen strategies for winter crops or preparing land for spring drilling, accurate soil testing before spring remains one of the most effective ways to improve nutrient use efficiency, protect yields and maximise profitability.
In this blog, we’ll look at soil mineral nitrogen (SMN) analysis and how much is available in your soils for crops this spring. We’ll also help you plan your soil testing ahead of spring cropping.
Understanding soil nitrogen supply (SNS)
One of the most common analyses carried out in laboratories at this time of year is SMN analysis. Agronomists and growers rely on this information to plan nitrogen applications accurately, ensuring crops receive what they need without unnecessary losses. Ultimately, accurate, reliable SMN data helps improve nitrogen use efficiency (NUE) and therefore profitability for your farm.
As soil temperatures rise above 5°C in spring, soil microbes become active and begin to mineralise organic material, releasing nitrogen and sulphur for crop uptake. This nitrogen may originate from soil organic matter (SOM), crop residues from the previous autumn, or recent organic manure applications. However, winter rainfall can significantly reduce available nitrogen through leaching, meaning SMN levels are often at their lowest by late winter or early spring.
The AHDB Nutrient Management Guide provides typical soil nitrogen supply (SNS) values based on soil type, previous cropping and winter rainfall. These are expressed as SNS indices:
- Index 0: up to 60 kg N/ha
- Index 1: 61-80 kg N/ha
- Index 2: 81-100 kg N/ha
If you have a clear history of your cropping, then the AHDB tables are a useful starting point. However, they can be less reliable where soils have high levels of SOM, additional manures, or high nitrogen crop residues. In these situations, directly measuring your own SMN levels provides a far more accurate foundation for fertiliser planning, helping you avoid over-application and save money on unnecessary inputs.
Soil testing before spring: top tips for SMN sampling
For the clearest picture of soil nitrogen availability, soil cores should ideally be taken to 90cm depth, although 60cm samples can still provide valuable information on nitrate and ammonium levels. Sampling is best carried out from late winter through to mid-March, before any nitrogen fertiliser is applied. This is ideal timing as it provides a snapshot of SMN levels after winter losses and before spring mineralisation accelerates.
Soil testing before spring: preparing soils for crops
With many fields still to be drilled in spring, you now have a valuable opportunity to check wider soil nutrient status to give your crops the best possible start. Spring crops have a much shorter nutrient uptake window than winter crops, making early nutrient availability critical for rapid establishment and strong early growth.
Phosphate, potash and magnesium are particularly important at this stage, especially for spring-sown legumes. Where soil indices are below target, fertiliser applications must compensate quickly, making SMN analysis once again a key tool before spring.
The Importance of soil pH
Soil pH has a major influence on the availability of all nutrients. Acid patches can significantly restrict nutrient uptake, even where soil indices appear adequate, so if you have them, now (before drilling) is the time to correct them.
Granulated lime applied at rates of up to 500kg/ha can rapidly and effectively address low pH, improving nutrient availability and root development.
The importance of phosphate for early establishment
All spring-planted crops rely on fresh phosphate as soon as roots begin to develop. Smaller seeds contain limited phosphate reserves, and because phosphate is largely immobile in soil, roots must physically grow through the soil to access it.
Applying water-soluble phosphate, either as compounds or ammonium phosphates, is the most effective way to support early establishment. Rates should always be adjusted according to soil analysis results.
Managing potash and magnesium with soil testing before spring
Potash demand increases rapidly during the main growth phase of all crops. While much of the potash taken up by crops is returned to the soil as they ripen, crops harvested green remove significantly more, depleting soil reserves quicker. Maintaining an appropriate soil potash index is essential to support early root development and optimise uptake. Soil analysis data will help select the required ratio of phosphate and potash in fertiliser.
Magnesium is another key nutrient that can be overlooked. As a central component of chlorophyll, magnesium plays a vital role in photosynthesis and greatly influences yield. Demand is particularly high in root crops such as potatoes and sugar beet, where a minimum soil index of 2 is required, while cereals perform best at index 1.
Where levels fall below target, magnesium applications should be planned accordingly: typically, every four to five years to maintain soil reserves. For example, as brassica crops ideally require index 2, 100kg of MgO should be applied at index 1, and 150kg at index 0.
How NRM can help
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.
Contact your agronomist, advisor or soil sampling provider to arrange testing and ensure your soils are ready to deliver their full potential in spring 2026.
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