soil-loss
PROTECTING THE LEAF
SOIL LOSS
Soil erosion can be high in the tropics, if steps are not taken to control it. Most important is to maintain some ground cover vegetation. Planting perennial crops, such as tea, should lead to less ground disturbance and more permanent cover than with annual crops. Nevertheless heavy rainfall can still result in high erosion rates where soil is exposed and specific erosion control measures should be taken in vulnerable areas. Demand for top soil for nursery use can result in degradation of extraction areas.
Good Practice
Soil Erosion
Plant along the contours if the land slopes significantly. This is particularly important on all slopes 25 degrees, where the additional use of a single row of Napier grass, after every ten rows of tea, can supplement contour planting. Napier grass can also be slashed for mulch or for fodder.
Construct silt pits (or micro-catchments) in newly planted areas, whatever the slope, to arrest run-off and encourage water retention. The design and construction of pits must take field safety into consideration and the pits must be maintained.
Carry out environmental impact assessment and discourage the use of mechanical harvesting machines in all areas where soil erosion is likely to be severe.
Pay careful attention to drain design and maintenance. Lock and spill over drains, boundary drains and stone revetments are advisable, wherever practical. A drain cut across the slope will have lower flow velocity resulting in less erosion. Soil drains should be planted with suitable grasses or other cover to hold the ground firm, but this cover must be maintained to ensure adequate flow.
Ground cover plantings (e.g. Nilgri daisy, yellow daisy, Citronella) along field edges can significantly reduce erosion.
Ground Cover
Plant a cover crop as early as possible after clearing. Broadcast oats as soon as land preparation is complete and/or choose a suitable local alternative such as beans, finger millet or maize which can be slashed before flowering and used for fodder.
Top Soil Use For Nursery
Top soil should be sourced to avoid degradation of extraction areas. Traditionally, forest soil was used for nurseries. Nursery soil should be taken from the areas to be planted, so that the soil is returned to the field during planting.
Potential Areas For Improvement
Investigate the planting of legumes as a ground cover in young tea, instead of oats. Mimosa and horse gram are possibilities.
Extend the use of tea prunings to cover all bare soils that could be liable to significant erosion.
Other suitable mulches should also be used if available.
Review the length of the pruning cycle to reduce the frequency of soil exposure. In areas very favourable for bush growth, hard plucking could limit table rise to the extent that fields can be plucked for five years rather than the conventional four. However, this practice will not be sustainable in some climatic zones, where it may lead to quality decline and increases in pests and diseases such as Helopeltis, Shot Hole Borer, Mites and Thorny Stem Blight.
Explore alternatives for using less soil in the nursery, in bags and for rooting cuttings, including the use of renewable rooting media instead of soil/sand.
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