Soil survey method and soil handling in an ALC report
Published regional maps cannot resolve a single field. What a detailed Agricultural Land Classification survey records, how the 3a to 3b boundary is reached, and how soil is handled on site.
The soil resource agricultural land classification section is the part of the report that a case officer, a landscape consultant and Natural England all read differently, and the part most often produced from the wrong data. Published regional maps are not a substitute for a field survey. They were drawn at a scale that cannot resolve a single field, and an application that relies on them to claim a site is Grade 3b will be challenged on exactly that point.
What the grades describe
Agricultural land in England is graded 1 to 5 under the revised guidelines published in 1988, with Grade 3 subdivided into 3a and 3b. The grade reflects the degree to which physical or chemical characteristics limit agricultural use, in flexibility of cropping, yield and consistency of yield.
Grades 1, 2 and 3a together form best and most versatile land, and that is the category planning policy protects. Grade 3b, 4 and 5 are not protected in the same way, which is why the boundary between 3a and 3b is where almost every argument happens.
The limiting factors fall into three groups. Climate comes first and is assessed from interpolated data: accumulated temperature, average annual rainfall, field capacity days and the moisture deficits for wheat and potatoes. Site factors follow: gradient, microrelief and flood risk. Soil factors come last: texture, depth, stoniness, wetness class and droughtiness derived from available water capacity.
Climate and site can cap the grade regardless of how good the soil is. A soil that would otherwise be Grade 1 sitting on a 12 per cent slope is not Grade 1.
Field survey method, auger points and pit density
A detailed Agricultural Land Classification survey is a systematic grid of auger borings, conventionally at 100 metre intervals, which gives one boring per hectare. Each boring records horizon depths, texture by hand assessment, stone content, colour and mottling, structure where it can be judged from an auger core, and depth to any restricting layer.
Soil inspection pits supplement the borings, dug at a lower density to allow structure, packing density and rooting depth to be seen properly. Texture assessed by hand from an auger core is reliable in experienced hands but cannot show structural condition, and wetness class depends on seeing mottling and gleying in an undisturbed profile.
The report should state the grid used, the number of borings, the number of pits, the surveyor's name and qualifications, and the survey date. A survey that gives a grade without giving the boring density has not shown its method, and a reviewer should ask for the field sheets.
Where the site is large and clearly uniform, a reduced density can be justified, but the justification has to be in the report rather than in the surveyor's head. Where the site is variable, expect more borings rather than fewer.
Ground conditions that invalidate a survey
Soil surveys are possible in most months and reliable in fewer.
Frozen ground defeats augering and prevents any judgement of structure. Waterlogged ground makes texture assessment by hand misleading, because saturated soil moulds differently. Very dry, hard ground stops the auger reaching depth and hides mottling patterns. A standing crop physically blocks access and, more subtly, means the surveyor cannot see the surface condition.
None of these makes a survey impossible. They make it contestable. A report that records a survey carried out in February on saturated clay, without commenting on the limitation, is inviting Natural England or an objector to say the wetness class is unreliable. Record the conditions, record the limitations, and where a return visit was made say so.
Identifying best and most versatile land
The 3a and 3b boundary is decided by the interaction of wetness and droughtiness with climate, and it is where a competent soil scientist earns their fee.
| Input | Where it comes from | Why it is contested |
|---|---|---|
| Climate data | Interpolated from national datasets to the site's altitude and location | Altitude corrections change field capacity days and the resulting grade |
| Soil wetness class | Field observation of gleying and mottling, plus drainage status | Existing field drainage may or may not be counted |
| Droughtiness | Available water capacity from texture and depth, against crop deficits | Stone content estimates move the calculation materially |
| Gradient | Survey or accurate topographic data | Averaged gradients hide steeper sub-areas |
| Depth to restricting layer | Auger and pit observation | Shallow soils over rock or gravel cap the grade |
Two practical points. Existing artificial drainage is a live question in many reports, because a field that is only workable because it was drained fifty years ago may be assessed differently depending on the condition of that drainage now. And stone content is estimated visually in the field, so two surveyors can produce different droughtiness results from the same profile. Both should be discussed rather than asserted.
Where non-agricultural development would affect more than 20 hectares of best and most versatile land, Natural England is a statutory consultee. Below that threshold the council forms its own view, usually on the strength of the survey in front of it.
Soil handling, storage and reinstatement
The second half of the section is what happens to the soil during construction, and it matters most on solar, infrastructure and large residential sites where land is returned to agriculture or to landscape afterwards.
The reference document is the Defra construction code of practice for the sustainable use of soils on construction sites. The principles are simple and routinely ignored.
- Strip and move soil only when it is dry enough to handle without smearing, which in practice rules out much of the winter.
- Strip topsoil and subsoil separately and keep them separate throughout, including in storage.
- Keep bund heights low enough to avoid anaerobic conditions developing in the base of the heap, and seed bunds that will stand for more than one season.
- Restrict trafficking over stripped areas and use designated haul routes with a protective layer.
- Loosen compacted subsoil before topsoil is replaced, and check the depth of loosening rather than assuming it.
- Reinstate to the recorded original depths, not to a nominal figure.
A soil resource plan setting these out is commonly conditioned, and on a scheme where reinstatement matters it sits alongside the Construction Management Plan rather than inside it.
Reporting for a solar or infrastructure scheme
Solar applications turn on the proportion of best and most versatile land affected and on reversibility. The soil section should quantify the area in each grade, show it on a plan with the boring locations, and explain what happens to the soil during construction, operation and decommissioning.
Reversibility is a real argument when it is evidenced and a weak one when it is asserted. Pile-driven mounting systems disturb very little soil. Concrete ballast, access tracks, substations and cable trenches disturb a great deal more, and the report should quantify the permanently affected area separately from the area beneath the panels.
Grazing between and beneath arrays keeps the land in agricultural use, and saying so is legitimate. Claiming that soil quality improves over a period without evidence is not, and an inspector will notice the difference.
Where the visual case runs alongside the soil case, the two should agree with each other on the extent and location of development, which sounds obvious until you read a pair of reports prepared by consultants who never spoke. The methodology for the visual side is covered in our note on photomontage methodology in a landscape and visual assessment.
Where surveys get challenged
Four challenges recur, and all four are avoidable.
Reliance on the published regional maps rather than a field survey. Survey conditions unrecorded. Boring density below the conventional grid with no justification. And a grade conclusion that does not follow transparently from the recorded wetness class and droughtiness values, because the intermediate working was left out.
Include the working. Tabulate the climate inputs, the wetness class and droughtiness for each mapping unit, and show how each unit reaches its grade. An officer who can follow the arithmetic will accept the conclusion, and an objector who cannot find a gap will move on to something else.
An Agricultural Land Classification survey needs a soil scientist, and professional review is strongly advised before submission. Browse all 66 PlanScope report types to see what else a countryside scheme is likely to need.
This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.
Frequently asked questions
What counts as best and most versatile agricultural land?
Grades 1, 2 and 3a under the revised 1988 classification. Grade 3b, 4 and 5 fall outside the protected category, which is why the boundary between 3a and 3b is where most disputes happen. That boundary is decided by the interaction of soil wetness and droughtiness with interpolated climate data for the site.
Can I rely on the published regional ALC maps?
Not for a site-specific case. The regional maps were drawn at a scale that cannot resolve individual fields, and a claim that a site is Grade 3b based on them will be challenged. Commission a detailed field survey where the grade matters to the outcome of the application.
How dense should the auger grid be?
A detailed survey conventionally uses a 100 metre grid, giving one boring per hectare, with soil inspection pits at a lower density to see structure and mottling directly. A reduced density can be justified on large uniform sites, but the justification has to appear in the report rather than being left unstated.
When is Natural England consulted about agricultural land?
Where non-agricultural development would affect more than 20 hectares of best and most versatile land, Natural England becomes a statutory consultee. Below that threshold the local planning authority reaches its own view, usually on the strength of the submitted survey and any objections raised about its method.
What goes into a soil handling plan?
Stripping only in dry conditions, separating topsoil and subsoil throughout, limiting bund heights to avoid anaerobic conditions, restricting trafficking over stripped ground, loosening compacted subsoil before topsoil is replaced, and reinstating to recorded depths. The Defra construction code of practice for sustainable soil use is the reference document.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.