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Water harvesting and soil moisture retention - chapter 9

Reducing evaporation losses and optimizing the use of soil moisture Windbreaks can be non-living structures such as brushwood and woven palm-frond fences or living hedges such as lines of shrubs, trees or tall grasses. In areas prone to wind they give shelter to crops and reduce evaporation of soil moisture | 9 Reducing evaporation losses and optimizing the use of soil moisture 9.1 Windbreaks Windbreaks can be non-living structures such as brushwood and woven palm-frond fences or living hedges such as lines of shrubs trees or tall grasses. In areas prone to wind they give shelter to crops and reduce evaporation of soil moisture because wind low to the ground is prevented. On slopes or fields affected by strong wind live hedges or windbreaks are effective. In addition they reduce the speed of run-off and they living fences provide organic material to the soil through their leaves. Their roots open up the soil which improves infiltration. Siting Windbreaks and live hedges have to be sited at right angles to the most damaging winds Figure 35 . When windbreaks are planted across a hill side they should follow the contour lines. a direction of most damaging wind b crop land c windbreak d drainage channel e farm road Figure 35 Siting of windbreaks. Reducing evaporation losses and optimizing the use of soil moisture 77 Planting procedure Two examples will be given Acacia spp. and Napier grass. Acacia spp. may be established from seeds or seedlings. Seeds are sown in strips or hills. These are spaced at a distance of 0.5 to 1 m within a row the rows being 1 m apart. Napier grass is planted by cuttings in hills which are spaced 20-30 cm apart. The rows are 30-50 cm from each other. When you want to set up a tree windbreak grass strips can be planted on the windward side of the trees in order to protect the tree-seedlings against the wind. Grasses may be retained as ground cover once the trees are fully grown. Trees with little undergrowth can also be reinforced with loose branches near the ground. Windbreaks should not be too windproof otherwise damaging whirlwinds may form on the lee side. Suitable species for windbreaks Deep rooting species are suitable for windbreaks because they do not compete for moisture with nearby crops. The use of trees with high evapotranspiration like