Tea Cultivation

Tea requires a moderately hot and humid climate. Climate influences 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.

Climatic factors

Rainfall: The average annual rainfall in North East India ranges from 2000-4000 mm. However, more than the total amount, the distribution of rainfall matters a lot for sustained high yield of tea throughout the season. In the North East India, the rainfall distribution is not even. The excess rainfall in the monsoon months of June-September causes drainage problems. The average monthly rainfall during November to March is less than the evapotranspiration loss and the resulting soil moisture deficit affects tea bushes. If this dry spell persists for a longer period, tea plants suffer heavily and crop goes down in spite of having sufficient rainfall in the monsoons. Thus, adequate rainfall during winter and early spring is crucial for high yield. Seasonal variation of rainfall (long-term average) is given in the following table:

Average rainfall distribution in the North East India’s tea growing regions in mm

Season
UA
CA
NB
BV
Dooars
Terai
Darjeeling
Winter (Dec-Feb)
4
3
3
3
1
1
2
Pre-monsoon (Mar-May)
24
27
19
28
14
13
15
Monsoon (June-Sep)
66
63
72
62
79
82
77
Post-monsoon (Oct-Nov)
6
7
6
7
6
4
6
Total
2720
2065
2185
3000
3990
2965
2345

(UA: Upper Assam, CA : Central Assam, NB : North Bank, BV : Barak valley)

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. Maximum ambient temperature above 32°C is unfavourable for optimum photosynthesis more so if it is accompanied by low humidity. In the tea belts of this 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 of 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 RH favours growth of tea.

Day length: Day length 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 length 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 teabushes remain dormant during the winter season for about 3 months on account of the combined effects of short days and low temperature.

Soil

Tea grows well on high land well drained soils 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 growinn on such soils are liable to suffer from draught during dry period and water logging during the rainy months. There should not be any hard pan or concretions in 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 identify all major and minor topographical features needs to be carried out.