Identifying limiting layers

Soils under agricultural management often have well mixed topsoil compared with adjacent soils in semi-natural systems, where a layer of plant litter occurs on the soil surface. If soils become very wet or acid under agricultural management then the mixing of organic matter into the soil can slow down and a similar layer may form.

Soil management in agriculture can also change soil structure either deliberately through tillage or indirectly as a result of trafficking or livestock grazing.

Some soils have poorer soil structure in a distinct limiting layer. These layers may limit drainage and /or restrict productivity even where other layers in the soil have excellent soil structure.

Find out more about identifying limiting layers


When soils are wetter than their plastic limit, the soil may cohere and change shape easily – the soil can be rolled in the hands to form “worms” just like plasticine. If soils are grazed or trafficked when they are wetter than the plastic limit, then structural damage can occur.  Natural rounded aggregates are lost and flattened platy aggregates are formed.


The depth of compaction depends on the force compressing the soil, the contact area with the soil, the strength in the soil and the type of soil. Animal hooves and tyres of light vehicles compact the soil directly underneath and around the contact area; heavy vehicles compact the soil more deeply.

Compaction type

Typical causes

Surface capping

(0–10cm deep)


Grazing in wet conditions

High stocking densities


(10–15cm deep)


Rainfall on new cultivations

Silage and muckspreading operations.


Note the first wheeling creates 70% of the damage so use tramlines if possible.

Plough pans

(10–15cm deep)

Repeated re-seeding at one depth


Limiting layers

Where compacted aggregates are packed densely then they will markedly affect water movement and rooting. Observing the depth and type of the main limiting layer is important to guide site-specific management.