Deep Pipe Irrigation

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This is a system that uses an open vertical or near vertical pipe to deliver irrigation water to the deep root zone. It encourages a much larger root volume than other forms of irrigation and helps develop a plant that is better adapted to survive after watering is terminated. By delivering irrigation water through deep pipes rather than on the surface, tree roots tend to grow down rather than at the surface which can also benefit any intercropping annuals which tend to be shallow rooted. Weed competition is reduced by avoiding surface irrigation. Deep pipe irrigation works just as well on steep slopes as on level ground.

It is done with 2.5 – 3cm diameter pipe placed vertically 30-50cm deep in the soil near a young tree 2.5-7.5cm away for seedling trees up to 12cm away for larger trees. A screen cover of 1mm mesh can be added to keep animals out. Several pipes can be used for a larger tree if necessary arranged around the tree symmetrically. A series of 1-2mm holes should be spaced 5-7.5cm apart down the side of the pipe nearest the plant to allow water to weep into the soil at all levels (not only at the bottom) to facilitate root growth early on.

If shallow-rooted plants from containers are planted next to a deep pipe without weep holes, the roots may not make contact with the wetted soil. Similarly, a young seedling can dry out if a drip emitter is used to deliver water into the pipe even if it has weep holes. Growing plants in deep containers can minimise these problems.

Deep pipes can be filled from hoses, watering cans or fitted with a drip emitter. If a drip emitter is used then the deep pipe can be smaller (down to around 1cm diameter) and in order to ensure that the water seeps through the pipe at all levels, the drip water rate must be fast enough to fill the pipe or alternatively, the pipe can be tilted with the weep holes downwards so that the water runs over and through them. A battery-powered remote timer combined with a water tank can be set up at a remote site to irrigate once a week which should lead to good tree survival.

The advantages over buried drip systems include ease of access to the drippers in case of blockage.  Deep pipe irrigation can be used with low quality water (though not necessarily with drip emitters if they are likely to block up). The deep pipes can be collected at the end of the season for re-use. Experiments have demonstrated that deep pipe irrigation systems are very effective and more efficient than surface drip or conventional surface irrigation. Much larger effective rooting volumes are developed and the plants are better adapted to survive future dry spells. In very dry regions, long term survival and growth can be improved by including micro catchments to increase effective rainfall by the use of tree shelters to reduce water demand and by the use of mulches.