CLIMATE & SOIL FOR TEA CULTIVATION:
Tea requires a moderately hot & humid climate. Climate influence yield, crop distribution and quality. Therefore, before cultivating tea in a new area, the suitability of the climate is the first point to be considered. Tea grows best on well- drained fertile acid soil on high lands.
CLIMATE FACTORS
RAINFALL: The avarage annual rainfall in the Nort East India randes from 2000-4000mm. However, more than the total amount, the distribution of rain fall matters a lat for sustained high yield of tea throughout the season. In the Nort East India, the rainfall distribution is not even. The excess rainfall during November to March is less than the evapotranspiration loss and the resulting soil moisture deficit affects tea bushes. If this dry speel persists for a longer period, tea plants suffer heavily and crop goes down in spite of having sufficient rainfall in the monsoon. Thus, adequate rainfall during water and early spring is crucial for high yield. Seasonal variation of rainfall (long-term aberage) is given in the following table:
Temperature and RH : Temperature affects tea yield by influencing rate of photosynthesis and controlling growth and dormancy. In general, the ambient temperature within 13°C and 28-32°C is conducive for growth of tea. Maximus ambient temperature above 32°C is unfavourable for optimum photosynthesis more so if it is accompanied by low humidily. In the tea belts of the region, the average winter minimum temperature (Dec-Feb) remains below 12°C and there is hardly any growth during this period. Flushing commences from March with the rise in temperature. Winter dormancy however is the result in f interaction of short day length and low temperature. Low temperature causes slower growth and low yield in the hill district of Darjeeling in comparison to the plains of Dooars and assam. A humid climate and high TH favours growth of tea.
Day lenght: day lenght influences growth and dormancy in tea bushes. When days of less than 11hr 15 min duration last for at least six weeks tea bushes become dormant. Hence the lenght of growing season decreases with increasing distance from the equator seasonal dormancy appears from around 18° North and South latitudes. In the Northeast india (25°-27°N latitude), the tea bushes remain dormant during the winter season for about 3 months on account of the combined efforts of short days and low temperature.
Tea grows well on high land well drained soild having a good depth, acidic PH in the range 4.5 to 5.5 and more than 2% organic matter. Shallow and compacted sub-soils limit root growth. Tea plants growing on such soils are liable to suffer from draught during dry period and water lodding during the rainy months. There should not be any hard pan or comcretions on the subsoil within 2m depths. The depth of ground water table should not be less than 90 cm for good growth of tea. Catchment planning is required for improved soil and water management practices in a tea estate for which land survey designed to indentify all major and minor topographical features need to be carried out.
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