Soil constraints stop crops from growing as well as they might. Yields are often lower than expected from paddocks with soil constraints. In Western Australia, some soils are both non-wetting and have subsoil acidity. Soil mixing or inversion can tackle these constraints at the same time.
Soil mixing and inversion
The degree of soil inversion or mixing depends on the equipment. Mouldboard ploughs invert the soil. This buries the topsoil and brings seams of deeper soil to the surface. Square furrow ploughs achieve a similar result to mouldboard ploughs. Disc ploughs and spaders can mix topsoil into the lower soil material.
Soil mixing and inversion bury water repellent topsoil and bring wettable soil to the surface. This helps rainfall or irrigation infiltrate the soil profile.
Subsoil acidity can be treated at the same time. Lime works faster to change soil pH when it is incorporated. Deep working the soil puts lime directly into the subsoil where it is needed. It also brings some acid subsoil up to the surface where it can be treated with surface-applied lime.
A trial at Mingenew, WA, treated water repellency and acidity. The treatment was still delivering crop yield benefits eight years later. Combined ploughing and liming caused the biggest yield increase.
Soil mixing and inversion can also:
- bury weed seeds
- alleviate compaction to working depth
- improve plant access to nutrients, depending on seasonal conditions.
Which method for different soils?
Soil inversion works best on sandy soils with mild to moderate subsoil acidity. Inversion can be more effective for treating water repellency than mixing with a spader. It is also more profitable in loamy sands.
- strongly acid subsoils – these may be better treated with lime and soil mixing
- clay subsoils – soils need to have a suitable loamy sand to loam subsoil texture that can be brought to the surface
- soils with a dispersive clay subsoil as this can create a hard-setting surface layer
- infertile sand subsoils.
Soil mixing with one way and two way ploughing or spading are better treatment methods for these soils.
How often can you mix or invert soil?
Soil inversion is a ‘one-off’ activity, conducted once every 10 years or more. Long-term effectiveness depends on the clay content brought to the surface. More clay (to a point) reduces the rate and likelihood of water repellence re-developing.