The short answer. In England, the Farming Rules for Water require nutrient plans for cultivated land to use soil test results, no more than five years old, for pH, phosphorus, potassium and magnesium, and for nitrogen or an assessment of soil nitrogen supply. Those results guide lime and fertiliser. They do not tell you whether the soil itself is getting better or worse. Soil health covers structure, water, biology and organic matter as well as nutrients, and soil organic carbon is the measure that ties most of those together. Annual soil carbon measurement sits alongside the standard test rather than replacing it: the standard test tells you what to apply this season, and the carbon measurement tells you which way the soil is heading. Across our UK monitoring, projects with declining soil organic carbon averaged yield losses of 20 to 50% in the 2025 and 2026 droughts, while projects with stable or increasing carbon typically stayed within 5 to 15% of average.
What UK soil testing covers today
Under the Farming Rules for Water in England, if you apply organic manure or manufactured fertiliser to cultivated land, your plans must take account of soil test results for pH, phosphorus, potassium and magnesium that are no more than five years old when you apply. Nitrogen can be assessed from the soil nitrogen supply rather than sampled. Cultivated land means land that has been ploughed, sown or harvested in the last year, or that has received organic manure or manufactured fertiliser in the last three years. The Environment Agency enforces the rules, and your soil test results are one of the things an inspector will ask to see.
Many standard analysis packages also report organic matter, usually by loss on ignition. That figure is useful as a rough guide, but it converts to carbon with an assumed factor and it is not precise enough to measure a change in carbon stock.
What a standard soil test does not tell you
- Which way the soil is heading. A nutrient index every few years shows what is available to the crop, not whether the soil is improving or declining.
- The carbon stock. Stock needs the concentration, the bulk density of the soil and the depth sampled. A standard test measures none of that as a stock.
- The variation within a field. A composite sample gives one average for the field. The headland, the old field boundary and the wet corner can be doing very different things.
- How the soil will hold up in a hard season. Soil organic carbon governs structure, infiltration, water holding and nutrient availability, and when it declines it declines invisibly.
What soil health means on a farm
A healthy soil holds its structure, lets water in and holds it, cycles nutrients and supports the life that does much of that work. Organic matter is the thread through all of it, and soil organic carbon, the carbon within that organic matter, is the part that can be measured most precisely. That is why changes in soil organic carbon show up in yield: a soil that is gaining carbon is usually gaining structure and water holding too, and a soil that is losing it is losing both.
Where soil carbon measurement fits
Annual soil carbon measurement adds the part a nutrient test cannot see. We take real soil samples on every farm we monitor, analyse them by dry combustion in a laboratory accredited to ISO/IEC 17025, and tie them to satellite imagery at 100 mapped values a hectare, so every field has a map and a total rather than one average. The error is measured against samples the AI never saw and deducted in full, and the change is reported against your own baseline with the accuracy stated. What five years of monitoring show explains the link to yield.
Simple field checks, such as counting earthworms and assessing soil structure in a spade pit, add useful context between measurements. They are quick and cheap, and they help explain what the numbers are showing.
Putting it together
- At least every five years: pH, phosphorus, potassium and magnesium, and nitrogen or an assessment of soil nitrogen supply, to meet the Farming Rules for Water and plan lime and fertiliser.
- Every year, in the same window: soil organic carbon stock, field by field, to see whether the soil is improving and which practices are working.
- Whenever you walk the fields: earthworms, structure and how water behaves after rain.
Questions we are asked about soil health testing
How often should soil be tested in the UK?
In England, if you apply manure or fertiliser to cultivated land, the Farming Rules for Water require soil test results for pH, phosphorus, potassium and magnesium, and for nitrogen or an assessment of soil nitrogen supply, that are no more than five years old. Soil organic carbon is best measured every year, at the same point in the year, so that a change is real and caught while the fix is still cheap.
Does a standard soil test include organic matter?
Many do, usually by loss on ignition. It is a rough guide for the sample tested. It does not measure soil organic carbon stock or its change over time.
Is soil carbon measurement a legal requirement?
Not in England. In Scotland, soil analysis for the Whole Farm Plan must now include soil carbon if you claim support payments, and in Wales the Sustainable Farming Scheme asks for soil organic matter to be tested. A standard laboratory test meets those. Measuring the change in soil carbon stock every year goes further: it shows which practices are building the soil and catches decline early, and it gives your buyers, lenders and insurers measured evidence when they ask for it. More in farm carbon audit or soil carbon measurement.
Does soil carbon measurement replace my nutrient testing?
No. They answer different questions. The nutrient test tells you what to apply this season. The soil carbon measurement tells you whether the soil is getting better or worse.
How do I get started?
Send us your SBI number and your hectares and we will send a written quote within two working days. Minimum project area 150 hectares, and it does not have to be your whole farm.
Part of soil carbon measurement for farms: the complete guide. Related: soil carbon testing in the UK: the methods compared · what soil organic carbon is · soil organic carbon and yield · farm carbon audit or soil carbon measurement.
