Soil Structure Decline

Soil structure decline is a phenomenon caused mainly by excessive tillage. DPIRD estimates the cost of lost crop and pasture production from subsoil compaction at $330 million for WA’s agricultural soils. Soils with poor structure typically exhibit symptoms of ‘crusting’ and ‘hard-setting’ of the surface. Degraded soils are characterised by reduced infiltration, increased runoff and increased compaction. Ideal soil structure has a large proportion of aggregates from 0.5 to 2 mm, which are not easily broken down.

What Causes Soil Structure Decline?

1. Excessive and/or poorly timed cultivation (especially wet soils);
2. Stock trampling (especially wet soils);
3. Loss of organic matter through stubble burning and/or tillage; and
4. Compaction by vehicles.

Solutions and Preventions

• Reduce tillage frequency and time it to occur when soils are not excessively wet or dry;
• Consider tilling areas of high structure decline to break up compaction and improve water holding capacity e.g. deep ripping, mould boarding, spading etc.;
• Reduce vehicle compaction by controlling vehicle movement;
• Remove livestock from paddocks before overgrazing occurs; and
• Fence or carefully managing stock access to fragile soils e.g. near waterways.

Further Reading

Armstrong, R. D., Eagle, C. and Flood, R. 2014. ‘Improving grain yields on a sodic clay soil in a temperate, medium-rainfall cropping environment.’ Crop and Pasture Science. 66(5): 492-505. http://www.publish.csiro.au/cp/cp14210

Australian Soil Club. Accessed 26/04/2018. ‘Soil Structure and Soil Texture: How do they affect Soil Health and Fertility?’ http://www.soil.org.au/resources/vol3_a2.htm

Davies, S. and Lacey, A. 2011. ‘Subsurface compaction a guide for WA farmers and consultants.’ Department of Agriculture (WA). https://researchlibrary.agric.wa.gov.au/cgi/viewcontent.cgi?article=1206&context=bulletins

Department of Primary Industries and Regional Development (DPIRD). 2017. ‘Deep ripping for soil compaction.’ https://www.agric.wa.gov.au/soil-compaction/deep-ripping-soil-compaction

Grains Research and Development Commission (GRDC). 2018. ‘Carbon storage for healthy WA soils.’ https://grdc.com.au/archive/key-issues/carbon-storage-for-healthy-wa-soils/details

Liebe Group. 2011. ‘Revisiting Gypsum for improved soil structure.’ http://liebegroup.org.au/wp-content/uploads/2012/01/Revisiting-Gypsum-for-improved-soil-structure-2011.pdf