Musings on the Agricultural Land Classification system

In this post, Alex Cooke discusses the use of the UK’s Agricultural Land Classification (ALC) in planning policy from her prior perspective as a practising soil-scientist.

Foundation for the ALC system

In 1941 Hans Jenny published his famous ‘CLORPT’ equation[1] which stated the basic factors affecting soil formation: climate (C); land use (L); organisms (O); relief (R); parent material (P); time (T). Differences in the factors results in the formation of different soil types. The Agricultural Land Classification (ALC) system  encompasses these factors, amongst others, resulting in the identification of different soil types and agricultural land productivity grades.



Development of the ALC system

First developed in 1966, the ALC system was introduced as a way to guide future development by identifying, and subsequently protecting, the most productive agricultural land. National soil surveys were undertaken and ALC grades published by 1974 at the 1:250,000 scale[2], under the former Ministry of Agriculture, Fisheries and Food (MAFF), now DEFRA. Five grades of land were identified ranging from Grade 1 (excellent quality) to Grade 5 (very poor quality), reflecting differences and extremes in the limitations to agricultural production – based on climate, soil type, drainage (wetness/droughtiness), relief, stoniness, erosion etc.


In practice the 1:250,000 scale was inappropriate for ALC determination at the field-scale as it did not reflect localised differences. As a result, a revision to the ALC system was introduced in 1976. This is the system used today where Grade 3 is separated into grades 3a and 3b. Consequently, the best and most versatile (BMV) land is classed as Grades 1, 2 and 3a, and is protected from irreversible loss arising from development by Natural England [3]. This productive agricultural land is essential to reduce the declining food security of the UK [4], a decrease which is predicted to continue due to future climate and environmental pressures[5].

ALC, Policy and Industry

Paragraph 112 of the National Planning Policy Framework (NPPF) refers to the protection of BMV land [6], to allow continued agricultural production. These policies are enhanced through the National Planning Policy Guidance [7] which provides guidance on the technical aspects of the ALC system.

The NPPF is there to guide Local Planning Authorities (LPA’s) in the development of their Local Plans; which state planning policies applicable within an authority area [8]. These are used to decide planning permissions and must align with the NPPF. Under the most recent wave of Local Plans, many LPA’s have done away with policies which definitively protect BMV agricultural land, instead referring to ‘sustainable protection’ of soil resources. This is a result of the lack of specificity regarding the protection of BMV land within the NPPF, where the protection of BMV land is simplified stating that LPA’s are to ‘consider the wider economic benefits of the agricultural land’. This leaves a wide interpretation of the policy, and allows industry to justify large scale development and the loss of agricultural land within planning law.

Developers who wish to develop areas of agricultural land exceeding 1ha have to undertake an ALC survey to inform the planning application and/or Environmental Impact Assessment (EIA) of said development. Subsequently, an ALC soil survey is undertaken according to the ‘Revised MAFF Guidelines’ [9] and the results used to calculate an ALC grade per auger bore. Results of individual augers are then interpolated to produce a map of the ALC grades of the site. Areas identified as BMV are given preferential protection from development over lesser quality agricultural land. Due to the lack of soil scientists in the UK and the decreasing number of younger people undertaking soil-related training there is an increasing knowledge gap, and consequently, this had fed into industry resulting in fewer companies offering soil/ALC services.

Issues surrounding ALC application

Development on Greenfield sites has increased due to a housing shortage, with LPA’s to build 3 million new homes by 2020 [10]. Consequently, large areas of the most productive agricultural land are increasingly at risk from irreversible loss. However, the soil/ALC skills gap decreases the reliability of new ALC surveys undertaken, and consequently the protection of agricultural lands are at risk.

Furthermore, the lack of policies within Local Plans referring specifically to the protection of BMV land has resulted in industries justification for increasingly large and damaging developments on agricultural land. The use of policies referring to the ‘sustainable protection’ of soil resources further highlights the lack of understanding surrounding the specifics of soil-systems within government, and therefore the subsequent need for soil science education and training.

Example of before and after development - Cheltenham, Gloucestershire

Example of after (left) and before (right) development – Cheltenham, Gloucestershire (click on picture for link to source)

Part of the need for accurate soil/ALC surveys can be met through the production of previous surveys under current ownership of private companies. Natural England holds a number of post-1988 ALC surveys undertaken by MAFF, however, there currently isn’t a platform where previous surveys undertaken by private companies can be obtained and collated together. If this could be achieved it would be realised that large areas of the UK have been subject to multiple ALC surveys, and therefore do not require as extensive a survey in the near-future if development on that land was proposed. Ultimately, this would lighten the pressure on the skills gap in the short term.


The ALC system has proven itself to be a reliable, accurate measure of the agricultural productivity of an area and is widely used in planning policy. However, ALC is at risk of dissolving unless measures are put in place to properly enforce it within National and Local planning policy, and within Industry. How are we to help meet food security targets if our agricultural land is being permanently taken out of production?
It is clear that the issues surrounding the application of the ALC system today are mainly a result of a poor understanding of soil-systems and the benefits they bring. This itself is a result of a decrease in soil science education and training. Soil has finally been recognised as a key resource (especially in 2015), however this recognition has not been adequately fed into policy and industry, and consequently, our agricultural lands are at risk.


Author: Alex Cooke

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