Native Grasses for Erosion Control
The control of soil losses following disruption is vital in preserving soil volume. Once lost to a property, soil is not replaced as the weathering processes required to break down stones and rocks is far too slow to quickly and adequately return soil to eroded landscapes. While it may be possible to build the organic content of soil and to capture some soil particles as they move across the soil, these additions do not, of their own, create new soil. Thus it is vital to not lose soil off a property.
Causes of erosion
Erosive forces such as wind and heavy rainfall cannot be stopped as they are outside of human control but their effects can be minimised by providing the soil with a full grass cover at all times. Having a perennial grass cover that is adapted to the environment is an ideal method of reducing erosion as long as it is accompanied by appropriate grazing management to help to retain a full cover at all times.
Establishing a grass cover on exposed or disrupted areas is an essential part of good soil management and erosion control. But achieving this with grasses that are sometimes slow to establish is a difficult operation. For example, while it might be ideal for an area to have a cover of spear grass and wallaby grass, these two grasses are very slow to establish and their seedlings will not hold the soil together in any appreciable way for a number of months after sowing.
So how do we hold the soil together in the meantime? We often suggest sowing with a cover crop of a cereal which will establish quickly and provide a fibrous root system that will hold the soil in place. If the cover crop is not sown too densely it will not be too competitive with the new seedlings and they will develop underneath the cereal crop almost unaffected. Care needs to be taken using this approach not to allow the cereal crop to go to seed, otherwise this will become next years weed problem and will continue then to be competitive with the native grass ground cover.
Cover crops such as Ryecorn, (or cereal rye), Japanese Millet, Barley, wheat and so forth can provide a good cover for an emerging grass. We have successfully established both wallaby grass and weeping grass underneath covers of barley and wheat to control erosion, and clients have also been very successful with covers of Jap Millet and Ryecorn.
Care needs to be taken with erosion control to sow at a low enough rate – 20 kg/ha of the cover crop is usually recommended, but it can go up to 30 kg/ha, but no more. Where possible the cover crop and the sown grass should be sown in alternate rows of a combine as if they are sown in the same row they will be competing with each other for water and nutrients.
Once the cereal crop has been mowed off and has died at the end of the first year, there should be numerous small plants of native grasses now able to access light, water and nutrients.
For grasses other than weeping grass and wallaby grass this may be more difficult, especially for the upright and faster-growing plants such as Barbed wire grass and Kangaroo grass.
We are often asked about the use of sprayed on mulches for erosion control. Results have been patchy with sprayed on mulches and it seems that the inclusion of high contents of paper cause many issues with successful establishment. We have had some successes with paper mulches, but they are not frequent and we have much higher rates of success with loose fibre mulches. We have also had success with deep mulches of materials such as potting mix or loose composts with depths of up to 50 to 60 mm still yielding positive results.