agricultural production guidelines
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Veld in KwaZulu-Natal
Co-ordinated Extension KwaZulu-Natal Veld 2.3 1999
ELECTRIC FENCING AND VELD MANAGEMENT
C I Macdonald
KwaZulu-Natal Department of Agriculture
INTRODUCTION
In this guideline points to be considered when planning to use electric fencing are highlighted. Detailed information on the use of electric fences on the farm is presented in Production Guideline 9.1 of this series.
Veld management systems by nature are managed ‘extensively’ and livestock are often attended to only once or twice a week. An electric fence network, by contrast, must be monitored on a daily basis. Any faults detected must be attended to immediately, simply because an electric fence is a psychological and not a physical barrier, and relies solely on a high voltage at all times as a deterrent. While the daily monitoring of the network is not a time-consuming activity, isolation and repair of the fault can be extremely time consuming, particularly if something else had been planned for that morning! A badly maintained/operating electric fence is an absolute curse - something to be avoided at all costs.
If the farmer is prepared to utilize such a fencing system in his veld management programme and build it properly and correctly, electric fencing can be (and indeed has been) used successfully as a grazing management tool. The greatest advantage of electric fencing over other more conventional types of fencing is its cost-effectiveness. While the management objectives of both types of fencing are the same (e.g. fencing of homogenous areas, and controlling the periods of stay and period of absence) roughly three times the distance of fencing can be erected using electric fencing for the same capital expenditure when compared with conventional fencing. This means that far more camps can ultimately be created with a commensurate increase in effective, overall control of the veld management system.
An important consideration, especially in the Tall Grassveld, is the effect of herbage growth contacting the electrified wires. Such contact results in a drop in voltage throughout the entire network. Fence lines must therefore be kept relatively free of herbage growth throughout the year, even during the winter after the plants have died back. Experience has shown that late winter and autumn are the times of year when voltage fluctuations are greatest, especially following a heavy overnight dew. For instance, if a voltage reading is taken at 08h00 and compared with one taken at midday, a difference of up to 3.5 kV can be recorded. The cause of this is the increased conductivity of the wet vegetation.
Autumn is also an extremely busy period on most farms (with the establishing of winter pastures, making silage etc.), and the clearing of the fence lines tends to be left over until early winter. By this time the livestock have invariably learned to get through the electric fences, and retraining of animals has not proved to be easy. Other longer-term alternatives for controlling vegetation have been attempted, but none have proved particularly successful (e.g. spraying herbicides, old engine oil and stock salt solution onto the herbage in an attempt to retard its growth). Most farmers therefore resort to a spring burn (where possible) and thereafter use a motorised brush cutter with a good operator to keep the herbage off the lines during the growing season.
Careful and detailed planning is required before building the fence. The following points should be considered.
Planning an electric fence
- Soil type. By virtue of their soil-moisture holding capabilities, clay soils are good conductors of electricity. An ‘all-live’ wiring configuration can and should be used. Sandy soils, by contrast, do not retain adequate soil-moisture to be good electricity conductors. A ‘live-earth-live’ configuration must therefore be employed. Such a configuration must be kept free of all herbage. Ease of access for fence maintenance therefore becomes a top priority when siting fence lines. Whatever fence configuration is employed, ensure a good earth return circuit under all conditions.
Animal production system
The production system will determine the number of strands of wire that are required (and the distance between each strand). The number and length of ‘live’ strands in turn determines the size of energiser necessary to power the network. Another factor which influences the choice of energiser is whether or not a fence-voltage monitoring device is to be used or not. (Should such a device be deemed necessary the fence strands must be connected in series and not in parallel. Series-connected strands have a higher resistance to voltage flow and therefore require a more powerful energiser).
- Veld management practices. Veld burning is invariably part of the management strategy. Fire-proof insulators, steel wire and hot-dipped, galvanised line-clamps are therefore necessary. (Beware of porcelain insulators - they crack and ‘leak’ very easily causing faults which are difficult to identify.) Plastic insulators and poli-wire are unsuitable as permanent ‘fixtures’.
Other considerations
It is strongly suggested that a robust digital volt meter be acquired. Experience has indicated that cheaper, alternative volt meters are easily broken and totally unreliable. The following minimum voltages must be maintained in the fence to ensure effective livestock control:Cattle (incl. calves) - 1000 volts
Sheep and goats - 2000 volts
Game - 4000 volts
Security fencing - 5000 volts
In conclusion therefore, electric fencing can be (and has been) used effectively in a veld management programme - provided it is built properly, and regularly monitored and maintained.