You have come to know how a tradition of growing shade tree in tea planations was built up in N.E. India and later spread to some other regions. It is already mentioned that from the beginning of the tea cultivation in Assam, Sau tree (Albizzia chinensis) was grown in tea plantations and considered as tea fertilizing tree. However, it was later realized that shade trees not only provide nutrients to the soil, but shade trees have many beneficial effects for the tea plants. Shade in tea is, thus, an integral part of tea plantation particularly in those areas where the leaf temperature rises to affect the photosynthesis and cause damage to leaves by scorching. If you are interested, you will learn hereafter the need and practice of shade growing in tea in N.E.India.
Why Is Shade Needed?
Air temperatures above 300C and below 130C are harmful for growth of tea plant. However, in the plains of N.E. India including Assam, the air temperature remains above 300 C for a greater part of the harvesting period and hence shade trees are interplanted in tea gardens to keep the temperature below a level where it cannot affect the photosynthesis adversely.
Wind velocity is useful in reducing high leaf temperature. However, the velocity of wind in the Brahmaputra valley in Assam is low due to the shelter effect of the hills on either side of the valley and for that shade is needed in a tea plantation to keep the leaf temperature down. However, in those areas where air temperature is high but the wind velocity is also high, shade is not needed. In Darjeeling where the ambient temperature is cool, shade is not required.
Benefits of Shade Trees
The benefits of shade trees are:
i) Shade trees keep down the leaf temperature to a beneficial range for maximum photosynthesis.
ii) They protect the tea plants from sun burning.
iii) Shade trees reduce the quantum of harmful portion of sunlight to fall on the crop canopy.
iv) Shade trees conserve soil moisture; protect the soil surface from impact of rain drops.
v) Leguminous shade tree species fix atmospheric nitrogen besides adding a large amount of organic matter in the forms of leaf litters.
vi) Shade trees turn over nutrients from lower soil layers and enrich the top soil.
vii) Shade trees favour partitioning of growth without affecting the quality of the crop.
viii) Attack of mites is less under shade.
ix) Shade trees minimize the hail damage.
x) In many occasions, shade trees act as a wind breaker.
xi) Shade trees create such a micro climate inside the tea plantation that enhances the growth of tea plants and thereby the yield, which cannot be achieved by artificial shading.
xii) Over and above, shade trees provide comfort to the workers while performing different operations in the field.
However, there are some disadvantages of shade trees inside the tea plantations. These are:
i) Shade trees may compete for moisture and nutrients with young tea during the years of establishment.
ii) Many shade trees act as alternative hosts for some pests and diseases.
iii) Shade trees hamper the mechanization inside the tea plantation.
iv) Falling of branches or uprooting due to storm causes damage to the tea plants.