About soil erosion
Soil erosion removes valuable topsoil which is the most productive part of the soil profile. The loss of this topsoil results in lower yields and higher production costs.
Soil erosion has declined across Australia over the past 70 years due to improvements in farming practices. Some soil losses still occur with extreme wind or rainfall events, and after severe or prolonged drought.
Types of erosion
Erosion can affect both the environment and land productivity. The main types land managers need to consider are wind erosion, water erosion and sheet erosion.
When wind and water remove topsoil and subsoil, it limits land management options. It also reduces the health and productivity of both land and aquatic ecosystems.
Grazing management also plays a major role, particularly during dry seasons and drought. The greatest risks occur when feed and ground cover from crops or pastures start to decline, especially in late summer and autumn.
Impacts of erosion
Some of the possible impacts of erosion on your farm:
- increased soil compaction
- loss of soil structure
- reduced organic matter in the soil
- reduced nutrients in the soil
- reduced ability of the soil to store water
- silt deposits
- increased salinity
- decreased water quality
- soil pH issues increased
- reduced ability of the soil to store water
- exposure of subsoil which often has less desirable physical and chemical properties.
Managing erosion
The first step for managing erosion is identifying the types of erosion you have.
Then prioritise which areas need addressing first by considering:
- the financial cost of each
- the time that will need to be allocated for control or repair
- subsequent management of the problem area.
Stages of water erosion
The diagram below shows the stages of water erosion
Splash erosion - water erosion starts with the splashing and impact of rain as it hits bare soil. The impact breaks up soil aggregates and causes splash particles. Soil then forms a crust that prevents infiltration and increases runoff.
Early signs of splash erosion include bare areas and water puddling as soon as rain falls.
Sheet erosion – runoff and overland water flow causes the loss of thin, topsoil layers. Overgrazed, cultivated or poorly consolidated soils with sparse vegetation are most vulnerable.
Early signs of sheet erosion include muddy runoff, visible grass roots, exposed tree roots, and exposed subsoil or stony soils. Soil deposits on the high side of obstructions such as fences may indicate active sheet erosion.
Rill erosion - rills are shallow drainage lines less than 30cm deep. They develop when surface water concentrates in depressions or low points through paddocks and erodes the soil.
Rill erosion is common in:
- bare agricultural land
- overgrazed bare agricultural land
- in freshly cultivated soil where the soil structure has been loosened.
Gully erosion - Gullies are channels deeper than 30cm that cannot be removed by normal cultivation.
Gullies occur when smaller water flows concentrate and cut a channel through the soil. Most gullies extend upslope as a result of the head of the gully being continually undercut and collapsing.
Stream and channel erosion - finally, the gully that was formed may transform into a running stream of water if enough rain persists.
Protecting soil from water erosion
Vegetation is the long-term solution to erosion.
Tussocky grasses can slow movement of water across the surface, while the roots hold the soil together. This minimises particles moving with the water flow.
Stock management in the immediate area is critical for repair. If the site is part of a larger paddock, a temporary electric fence can reduce grazing pressure and allow tussocky grasses to colonise. A short crash graze at some time may also be beneficial.
Options for managing each stage of water erosion
Increase groundcover to protect the soil from raindrop and wind impact
You can do this by:
- reducing stock access
- reducing tillage
- planting appropriate vegetation.
Slow down the movement of surface water
You can do this by:
- increasing groundcover and vegetation
- building mulch lines, grassed waterways and filter strips.
Spread out concentrated flows of water
You can do this by:
- building diversion banks and check dams
- building contour banks and ditches.
Control the rapid descent of water
You can do this by:
- installing drop structures
- diverting upslope run off.
Trap suspended soil
You can do this by:
- installing sediment traps and settling ponds
- planting on the contour.
Read more about erosion control structures.
Strategic fencing and infrastructure
Fencing is recommended for the protection of watercourses. Fencing is recommended for most gully systems where sodic or dispersible soils occur along the flow line. Excluding stock allows for natural regeneration to occur and reduces the possibility of further erosion on the gully edges due to stock tracks concentrating runoff.
Fence out a buffer zone of at least 10 metres either side to allow for further slumping, tree planting and vehicle access. Many landholders have been nervous about fencing off too much land. However, in the long term it is beneficial to have an extra buffer. These areas can be used in the event of a feed gap, or for stock protection after shearing.
Use a property plan to help locate fence position to ensure vehicle and stock movements, gates and water supply are considered.
Read more about on-farm management to prevent erosion.
Revegetation
Plant trees and shrubs along both sides of the gully banks to help stabilise the eroding area.
As well as stabilising the soil, this creates a wildlife corridor and windbreak benefits and improves water quality off site.
Read more about revegetation.
Contact Local Land Services NSW
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