Soil Structure

Jeff Harvie

What does “soil structure” actually mean? It refers to the way that the minerals and organic matter that make up the soil stick together and hold together when subject to forces. In all but extremely sandy soils, soil particles will form crumbs known as “peds”. When they do this, they create pore spaces between them which are available for: water infiltration, aeration and gaseous exchange for root and microbe health, and for easy root penetration. The quality of soil structure is in how well these peds form, and how resistant to external forces they are. A poorly structured soil will lose these peds, and therefore the valuable pore spaces, when subject to rain, cultivation and compaction from vehicles and animals. Root growth will be poor. Water will run off. Soils will become waterlogged and anaerobic.

What causes a quality soil structure? A combination of cation balance (especially sufficient calcium rations), organic carbon and good management. Calcium ions will create a strong ionic bond between soil particles, far more resistant to external forces than the weaker bonds caused by high levels of sodium and magnesium. Sodic soils, and high magnesium soils (eg. serpentine soils) will tend to turn to slush after rainfall and will pug with compaction. Humus is a sticky substance which will hold soil particles together, and the hyphae (pseudo root-system) of mycorrhizal fungi act like “string bags” in holding peds together.

Good management is in how well you balance these elements. Soil testing will show cation ratios and quantities that may need improvement through additions of calcium and leaching of sodium. Maintaining and improving soil organic carbon can be done through reducing cultivation (which breaks apart peds leaving them exposed to humus degradation), stubble/trash retention, organic matter additions and other practices and products which increase microbial activity.

Disclaimer: Information contained in these pages is intended to be generalised and non-specific. It is not intended to be specific advice for specific situations. No responsibility is accepted for any outcomes that any individuals or organisations may wish to attribute to applying this information.

[Printer friendly page | Send to a friend]
Page created in 0.207034 Seconds