Main theme of soil conservation is to maintain an optimum soil moisture and soil-fertility for the normal growth of plant. Most plants are unable to thrive under either water-surplus or water stress. Tea plants do not grow well under these conditions. Soils are eroded and depleted from soil surface by excessive water flow or water logging. As a result, soil conservation of prime importance against soil erosion which is caused either by a heavy runoff (water erosion) or deforestation (wind erosion).( Sana, 1989.)
1. Conservation Measure:
Soil erosion becomes less serious after five years of planting when the land coverage is formed by a thick mat of vegetation, grasses, etc. and tea canopy. There are various ways of soil conservation that may be adopted in tea plantation, such as,
(a) Soil coverage by mulching, cover crops, and shade,
(b) Adoption of contour planting and
(c) Improvement of drainage system.
Cover crops protect the new plantation from soil erosion at a critical time. These cover crops also help the decomposition of the disturbed natural herbage, and compete with unwanted and rejuvenating weeds. Following conservation measures are necessary to check the soil erosion
- Follow Weed Control programme with persistent herbicides, viz. Diuron, Simazine or Dalapon after cleaning trees, shrubs in new site.
- Maintain a strip of forest on the ridge top when clearing the forest for extension or replanting.
- Keep a strip of old tea along the contour- 50 cm. width for moderate slope, and 100 cm. width for steep slope.
- Provide mulch regularly on edges of exposed sections, particularly south and south-western slopes / sides of mature tea sections during Nov-Mar.
- Established complete cover of tea at earliest possible time.
2. Land Drainage:
Drainage means removal of excess water from the root zone of the plant in the quickest possible time, without causing any injury to the standing crop. Impeded drainage results in restricted root-proliferation making the plants drought susceptible and more prone to many root diseases. The efficient drainage system aims at
(i) Removing surface and runoff water during excessive rain particularly from tillah and high flat areas,
(ii) Draining the excess water from areas with underlying Hardpan or Impervious Stratum and
(iii) Reducing the water table to a minimum depth of 1.0-1.5 m. during monsoon in flat areas.
2.1. Planning of drainage system:
An overall planning is necessary to design the drainage system for a tea estate. Because the poor drainage may result various problems and crop loss to the tune of 15-40% in the affected areas. Any improvement on drainage system is known to increase of crop yield to the extent of 9%.( Roberson, 1985.)
To construct a comprehensive drainage system for a estate, the topography and lie (gradient) of the land, soil-structure, catchment area locations of natural water-source should be surveyed.
2.2. Maintenance of Drains:
During monsoon, the water table may rise to the vicinity of tea bushes causing impeded drainage. If over-draining is suspected, the gradient of drains will be corrected. Besides, the impeded drainage may occur due to the presence of Hard Pan/Impervious layer underneath. Drains will be constructed 10-12 cm. below the level of Hard Pan. Following special Corrective Measures/Maintenance Procedures may be adopted.
· Drains must be clean and regarded during March.
· Regular inspection should be made during heavy rainfall.
· Removal of water from the root zone should be made by digging drains to a depth of 1 m.
· Pumping out water from the main drains during July-Sept to reduce the water table, if necessary.
· Construction of Contour paths, 50-70 cm. wide, with a gradient of 1 in 6 should be made to remove only surface runoff water.
· Construction of Contour Boxes, 50-60 cm. long, 15-20 cm. wide and 45-50 cm. deep, filled with separate layers of coarse sand, gravels and stones at the top will be made along the path to check the rate of water flow.
3. Shade Tree Management:
The use of leguminous trees as shade for tea is common in India, Sri Lanka, Indonesia, Bangladesh and Africa. In Sri Lanka and Indonesia some non-leguminous species, viz. Grevillea robusta, and deciduous trees are also used at high elevation where the leguminous shade species do not grow well. Shade management on India and Bangladesh, most common shade species are Albizzia odoratissima occupying about 75% of tea area, A. moluccana, about 7%; Derris robusta. 8%, A. procera, 4%; A. lebbeck and Cassia siamea about 3%. In some old sections, A. stipulata; A. lucida and Dalbergia assamica are also found.( Hasan, 1963.)
For a successful shade management, the correct selection of shade species on basis of its botanical characteristics, viz. foliage pattern, canopy structure, flowering behavior, economic life, etc is essential.
Table: 2 Nitrogen-Economy from leaf-falls.
| Shade species | Dry weight of leaf-fall | Nitrogen (kg/ha) |
| Albizzia chinensis | 685 | 19 |
| Albizzia odoratissima | 655 | 16 |
| Derris robusta | 623 | 16 |
| Albizzia procera | 466 | 11 |
