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Fixing erosion with turf

By David Mason-Jones

Turf is a product that has agricultural uses in the control of erosion. It is not just a cosmetic tool for landscaping parks and gardens in town where the owners want an instant lawn.

Because of the speed with which turf can be laid, it provides a rapid method of establishing grass cover to bare areas that have been caused by earthworks. A popular use of turf to stabilise earthworks occurs where an earth dam has been built and the property owner is now waiting for rain to fill it.

There is a sense of urgency for the property owner because a large amount of the bare earth wall can wash back into the dam or wash down stream if the first rainfall is heavy. The farmer is caught in a Catch 22 situation because the ground cover may not grow without rain germinating the seed but rain is the enemy of the bare earth wall.

The role of turf in such situations is also important because the earth and clay that has been used in the dam wall may come from deep in the soil profile where there is virtually no seed bank. Left alone the wall will not naturally regenerate with vegetation until a seed bank accumulates and this may take several seasons. Therefore, the option of using turf is one of the fastest ways of getting ground cover on the wall.

Other spots on a farm where the use of turf may be considered are places like gate ways which have been heavily damaged through stock use and which now need refurbishment.

Small bare patches in paddocks and the water catchment areas in small erosion gullies are also examples.

The entry point to a new dam or an old dam for that matter is also a prime target for treatment with turf. During the drought many farmers have either built new dams or dredged the old ones to remove the silt. On many occasions the amount of silt removed from a dam is alarming and the farmer needs to stop and think about the fact that all that silt had to be washed from the dam’s catchment, via a water course of some sort, and into the dam. Turf laid across the ground between the catchment and the point of entry to the dam will dramatically diminish the amount of silt entering the dam. While it may be costly to lay turf at such a site, the farmer needs to balance the cost against the cost of the alternatives regular hiring of excavators to desilt dams, loss of top soil and lack of water storage capacity in the next drought.

On a much larger scale turf may be used to assist in erosion control measures in large rivers. Such projects are normally out of the scope of a small farmer but, nevertheless, turf is used by large corporations, local government and environ-mental groups to help restore the landscape.

Typical grasses used in the agricultural use of turf are kikuyu and couch. Each of these grasses brings a particular benefit to the quick establishment of ground cover and, therefore, a common procedure is to plant the turf in alternate strips.

Also, where the overall expense becomes higher, it is common to separate the two by leaving some bare ground to separate the strips. When the grasses in the strips become established they will quickly send runners into the bare ground between the strips.

It is not necessary in the agricultural use of turf to cover the entire surface area with one long mat of grass as would desirable in a domestic building in a suburb.

Comparing the benefits of couch and kikuyu, couch has the advantage that it establishes a deeper root system than kikuyu and is therefore likely, once established, to hold in place more tenaciously against water or wind action than the kikuyu. The kikuyu is an invasive grass and will spread far and wide once it is established. Kikuyu is a good stock pasture and this means that the rehabilitated area will become an asset for controlled grazing in future.

An individual roll of grass will cover one square metre of earth and costs around $3.00 without delivery charges. Prices vary with the climatic conditions in different growing districts and the distance from the turf farm to the erosion control site will be a major factor in the eventual cost. One way for a property owner to reduce costs is to use a farm vehicle, such as a stock transport truck, to collect the grass from to the turf farm.

Prior to delivery the grass is cut to 50mm in height and the roots are cut off just below ground level. An extremely fine soil section about 1mm to 2mm in depth also comes with the roll.

In order to supply the rolls in this way the turf farmers harvest the turf the night before and deliver it next morning or harvest it early in the morning and deliver it that day. In this condition, with virtually no soil present and the root system cut very short, the turf is vulnerable to heat and lack of water if it is simply left alone.

The farmer must ensure that he or she has planned a work routine so that they are able to lay the turf immediately on its arrival at the farm.

Turf left stacked on-site in the heat for a few days without water will die.
A number of factors are important in making sure the turf holds well to the new ground.

A proprietor of turf supply company AgTurf Supplies, Glen Mead, advises, “It is a good idea to loosen up the top level of bare earth somehow. In the situation of a dam wall the bulldozer has often run across the face of the dam many times to compact it tightly down.

“Loosening up a small layer of top soil will do two things. Firstly it allows easier penetration of the new roots into the ground. Secondly it prevents water from simply running away across the surface of the ground beneath the turf layer when it is watered. Soft topsoil helps water soak in.

“Another good preparation is to place some nutrient or fertiliser on the ground surface where the new turf is to be laid. Chook manure is a good fertiliser for this purpose although the farmer should be cautious not to apply it too heavily.

“Once the turf is laid it is essential to keep it moist with daily watering. This may require watering twice a day in the heat of summer. Unless the farmer is prepared to allocate the labour hours and the watering resources to do this, it is probably better not to consider the turf option at all. The turf must be kept wet otherwise it will die.

“The farmer will soon see when the glass starts to take hold and the roots and runners start to grow. At that point he or she can leave off watering. If there is a sudden hot dry spell or hot winds, the watering should be started again,” he says.

Although some grasses such as kikuyu will do well all year round, the best time to lay turf is in the early Spring when natural conditions are best to stimulate growth.
If a property owner is contemplating a very large erosion control project using turf it may be advisable to coordinate with a turf farm some months ahead to guarantee a large supply of turf is earmarked for the contract.

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