Drainage is an important issue because most plants cannot survive waterlogging for more than a short time. Most plants need at least 10% to 15% of the soil pore to be filled with air to survive. Soil becomes waterlogged when its pores fill with water. Once the soil is saturated, root growth in most plants can occur only on the surface. When there is more water than the soil pores can hold, the water will collect in the soil surface and drain by gravity to the lowest point.
Surface drainage is the removal of water that collects on the land surface. Many fields have low spots or depressions where water ponds. Surface drainage techniques such as land leveling, construction of shallow ditches or waterways can allow the water to leave the field rather than causing prolonged wet areas.
Subsurface drainage removes excess water from the soil profile and reduces the watertable below the root zone. Subsurface drainage is used where surface drainage is not effective. With subsurface drainage, slotted polydrain is installed below the soil surface, covered by gravel to prevent soil particles from being carried into the drain and to improve the flow of the water.
TG Drains installs subsurface drainage using a laser controlled, purpose built drainage machine. The machine, a Mastenbroek 20/15 imported from England, can cut a trench up to 2.2 metres deep. The digging chain of the machine cuts a trench on the design grade and the drainage pipe is laid with the backfill of gravel in one single operation.
A tractor hauling a gravel trailer with a conveyor belt drives alongside the Mastenbroek machine to deliver a continuous flow of clean, fine gravel into the machine's hopper. This avoids slumping of the trench walls and prevents excavated material falling on the pipe and possibly blocking the drainage slots. The elevation of the gravel hopper at the back of the Mastenbroek machine can be altered hydraulically, allowing the thickness of the permeable gravel backfill to be varied according to soil type.
To assertain the optimum position of the drains we can take our own levels or, if a large part of the farm is involved, or a drainage plan is to be put in over a number of years we use farmmaps created by Farmworks .
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