Subsurface compaction a guide for WA farmers and consultants

For plants to grow in agricultural soils, roots and emerging shoots must be able to force their way through the soil. In soils of high strength, this growth is physically restricted. High strength soils may be due to natural soil characteristics and conditions or develop as a result of agricultural practices and may be in layers or throughout the soil profile. In agriculture, high strength soils commonly occur as a result of compaction. Compaction of agricultural soils can be in the surface (often caused by stock trampling or rain drop splatter) or in the subsurface (usually in a layer at 10–40 cm). Subsurface compaction has a different suite of effects and management options than surface compaction, although, subsurface compaction amelioration techniques may also benefit a hardsetting profile. Subsurface compaction can occur in most Western Australian agricultural soils. Some soils have greater capacity to resist compaction or to self-repair following compaction. However, nearly three-quarters of WA’s agricultural soils are either affected by, or highly susceptible to, subsurface compaction (Figure 1). Compacted subsurface soil restricts crop and pasture root growth with plant biomass correspondingly reduced. In most seasons this also results in grain yield reduction. The average opportunity cost of lost agricultural production is estimated at $333 million per year for the Northern, Central, Southern and South West Agricultural regions (Herbert 2009). The most common forms of subsurface compaction in WA agricultural soils are traffic and plough hardpans caused by agricultural equipment and are the focus of this guide. In most cases these hardpans can be economically remedied and appropriate agricultural practice can minimise the reformation of hardpans.https://library.dpird.wa.gov.au/bulletins/1206/thumbnail.jp