Tea is an agro-ecosystem comprising tea plants, shade tree and other ancillary crops along with various abiotic elements. The life processes of biotic community are critically balance with the tea biosphere which includes climate and soil. The climatic elements vary from place to place and season to season owing to the diversity of geological locations, the phisiography, the distribution of land and water, altitude, mountain barriers, ocean currents, semi-permanent high/low pressure-belts, wind, storms, etc. in a country.
Tea Climate:
Bangladesh climate is considered to be tropical monsoon with three distinct seasons: Warm season (mid Feb-mid May), Monsoon season (mid May-mid Oct), and Cold season (mid Oct-mid Feb). The climate of Bangladesh is discussed under three important parameters like Rainfall regime, Temperature regime, and Humidity-Evaporation cum Sunshine regime which are responsible for a successful tea culture.
Temperature rainfall and relative humidity are the most important factors for the growth and development of tea crops and cultivated best in temperature ranges from 12.70C-280C and rainfall ranges from 2500mm.-5000mm. and humidity ranges from 56-86%.( Zaman, 1980.)
Tea Soil
Texture and Topography of Tea Soil:
Soils of Sylhet Tea zone have different characteristics depending on age, drainage, and parent material. Soils in Hills are generally very steep, yellowish- brown, well-drained with a moderate blocky structure, and having bedded sand, sandstone or shale at a depth of 0.6-1.5m (2 to 5 feet), loamy to silty or clayey. Soils in Surma-Kushiyara Flood Plain are grey gradually stratified, silty and loamy occurring on gently undulating ridges and basins. The soils of Outwash Plain are mostly silty to clayey, grey with some melting in the subsoil and have weaker structure than the Flood plains. Most of the soils of Sylhet basin overlie stratified material at 0.6-1.5m 2 -5 feet depth, seasonally flooded, grey or locally deep grey with blocky structure.( Sana, 1989.)
Texturally, the tea soils in Bangladesh are predominantly loamy. Soils of Balisera, Monodoloi and Luskmipur circles are loamy to sandy loam from surface downwards, while loamy sand in north Sylhet circle, but soils in Chittagong zone are most loamy.
Topographically, tea zone of Bangladesh may be divided into 3 units, viz.
(i) Tillah or low hills which are outliers of the Tripura hill Range in India
(ii) High flat which are the higher valleys constitute about 45% of the land. The soils are suitable for tea cultivation.
(iii) Low flat which are the valley floor and constitute about 23% of tea land.
Geomorphology of Tea zone in Bangladesh:
Sylhet is situated between 23o59`and 25o13`-North latitude, and 90o54`and 92o29`50” East longitude, and covers an area of 12387 sq. km. (4785 sq miles). It is essentially a valley lying between the Khasi- Jaintia hills on the north and the Tripura hills on the south, and bounded by the Indian district, cachar on the east, and by the district of Comilla and Mymensing, Bangladesh on the west.
Sylhet, having widest variation in geomorphology and soil types, is divided into four landscapes: (i)Hills exceeding 300 m in height with shallow, stony and rocky soils, and predominantly wet basins with peat soils occurring within a few miles from each other, (ii) outwash plains occur in a band up to 6.44 km wide along the foot of most hill ranges, and cover most of the valley between the south Sylhet hills, (iii) Surma and Kushiyara flood plains which cover about 2/3 of two eastern sub-division, and (iv) Sylhet basin which is occupied by two subdivision, Sunamganj and Habijang,
