Soil structure and avoiding compaction

The presence of worms is a good indicator of soil health.
The presence of worms is a good indicator of soil health.

Soil structure and its degree of development are critical factors in determining the productivity of any soil.

Soils with well-developed structure have plenty of pore space to allow water and air movement deep within the soil which in turn allows for healthy root development and increased plant productivity.

Soil structure (known as crumbs, blocks or peds) forms naturally through the interaction of processes within the soil on its constituents (sand, silt and clay particles, humus):

q Physical – action of freeze/thaw and wetting/drying cycles

q Chemical – bonding of clay particles

q Biological – crumbs glued together with organic compounds and stabilized by fungal hyphae and fine roots

In general, for any given soil type, structure is most developed under long-term pasture and least developed under long term cultivation.

While soil structure will develop naturally it is susceptible to damage and can be slow to recover. Damage to structure can result in reduced water movement, increased anaerobic conditions within the soil with a subsequent reduction in root growth and plant productivity. Although soil structure can be damaged through over-cultivation, the main cause in Northern Ireland is via compaction by animals or vehicles when the soil is wet. Here the peds are at their weakest and prone to deform or breakup when a force is placed on them.

Given the vagaries of the climate that agriculture has to cope with, it is very difficult to reduce soil structural damage to zero, however, management is key and can be broken down to five areas:

1. Soil test regularly - to maintain nutrient levels at optimum in order to promote active structure development

2. Work with prevailing soil conditions - if possible postpone vehicular access to fields for 48 hours after heavy rainfall, or remove or reduce stock on susceptible fields

3. Reduce total axle loads (ideally below 5 t) - the higher the axel load the more potential for soil damage

4. Reduce ground contact pressure - in vehicles the tyre pressure and area of contact dictate the potential for damage - with animals, stocking on high tillering dense swards will have less of an impact than on open swards or recent reseeds

5. Control field trafficking - with vehicles as the majority of damage is caused in the first few trips it is worth designating a ‘sacrifice’ strip where the field traffic can be concentrated - with animals, especially dairy cattle, access to and from milking should be via hard standing laneways as much as possible

Farm Family Key Skills (FFKS) is a scheme under the Farm Business Improvement Scheme (FBIS) which is part of the Rural Development Programme 2014 - 2020 and receives co-financing from the European Agricultural Fund for Rural Development (EAFRD).

The Sustainable Soil Management Events are the latest in a series of FFKS workshops for farmers, farm family members and employees.