Better soil management

by Dr Will Stiles, Farming Connect Knowledge Exchange Hub, IBERS, Aberystwyth University

SoIL compaction is a major global issue associated with modern, mechanical agriculture. The use of heavy machinery and other modern agricultural approaches can have significant impact on soil and soil based processes.

Soil compaction is defined as a process where soil grains are rearranged to reduce void space, thereby increasing bulk density. Compaction can affect both the upper layer of soil (topsoil) and soil to depth (subsoil).

Subsoil compaction is a challenging problem as remediation of this is costly and difficult to achieve. It has been demonstrated to drive significant reductions in crop yield and as such, has been recognised as a serious form of soil degradation by the eU.

Soil becomes compacted when exposed to heavy machinery traffic, or through excessive animal trampling. Three components govern the degree to which a soil is affected: soil texture and structure, soil organic matter, and soil water content. The degree of organic matter in soil will influence the degree to which a soil is impacted by increasing the resistance of a soil to deformation and/or increasing elasticity potential.

Compaction effects form heavy machinery and livestock trampling are exacerbated in wet conditions. Typically, soils with high moisture content are more vulnerable to the impact of compaction as the strength of a soil is heavily dependent on water content. Timing machinery usage or grazing is therefore a key strategy for reducing the potential impact.

If left, soil will recover from compaction through natural processes, such as soil organism activity (e.g. earthworm burrowing) or seasonal wet-dry or freeze-thaw cycles. These can break apart soil, however this approach to recovery is slow and can take up to 18 years, depending on

severity of compaction and the soil type. Therefore, avoidance is better than remediation.

Modifying machinery, such as changing from wheeled to tracked vehicles, may reduce some of the impact, but overall, the intensity of machine traffic (number of passes) is the principal factor governing compaction rate. Controlled Traffic Farming is a system that utilises permanent traffic lanes, which are designed to be the only parts of the field that are exposed to machinery tyres.

This dramatically reduces the effects of compaction in the rest of the field. Controlled Traffic Farming is achieved through effective planning for field systems and can be aided by the use of precision navigation tools and auto steeringtechnology.

Soil compaction is a global challenge for modern agriculture, as this impact can reduce crop yield and increase the need for expensive inputs such as fertiliser and energy. By reducing this harmful influence, UK farms can enhance their potential for production and reduce environmental impact.

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