Humidity and precipitation for growing tea
Plants in general, to form one part of organic matter need up to 400 parts of water.
Tea is a moisture-loving plant, and provides the product of buds and young leaves, so it needs more water. However, tea is a plant that is afraid of waterlogging. If it is flooded or the soil has high water level, the tea roots will easily rot.
Rainfall requirements for tea plant growth:
– Total annual rainfall reaches 1,500 – 2,000 mm/year (preferably about 1800 mm).
– Except in irrigated tea areas, under the conditions of cultivation thanks to the rain, it is difficult for tea plants to grow normally if the rainfall is lower than 1150 mm.
– Average monthly rainfall required for tea plants to grow > 150 mm.month-1.
With a tropical monsoon climate, with two distinct rainy and sunny seasons, the distribution of rainfall creates problems for the tea growing industry in Vietnam: in the rainy season (May – October) concentrated rain causes danger. chance of erosion, leaching nutrients, soil, it is necessary to take measures to prevent erosion. On the contrary, in the dry season (November – March next year) lack of water, to avoid damage, it is necessary to apply root control measures.
Requirements for moisture of tea plants:
+ Soil moisture: 80 – 85% of the maximum moisture capacity.
+ Air humidity: 75 – 80% or > 80%.
However, in tropical regions, where the climate only has two rainy and sunny seasons, tea plants also need 1-2 months of sunshine to stop growing and complete their annual reproductive cycle. This is also the best time to cut and shape tea trees.
Temperature for growing tea
Air temperature plays an important role in the initiation, formation and growth of tea sprouts, thus affecting the tea bud harvest, the interval between two picking and the yield of the tea garden . In the range of 17-25oC, the shoot extension rate is linearly correlated with mean temperature (Squire, 1979).
The growth of tea plants according to the fluctuations of temperature was recorded as follows:
– From above 10oC: tea plants start to grow.
– The average annual temperature for normal growth of tea plants is 12.5oC; the minimum air temperature promoting the growth of buds is 13-14oC; The suitable temperature for tea plants fluctuates in the range of 18-30oC.
– If the daytime temperature is higher than 30oC or lower than 14oC at night, it can reduce the growth rate. The temperature is higher than 35oC, the rate of net photosynthesis and growth decrease rapidly. The accumulation of tannins in tea plants is inhibited. At 40oC, the young parts of the tea plant are scorched from the outer edge. The damage is even greater if the soil moisture is low.
For good growth, tea plants, depending on the variety, require a certain temperature range. The total temperature needed for tea plants to grow is 3500 – 4000oC/year. In the appropriate temperature range, the higher the temperature, the higher the tannin content in the leaves. Temperatures that are too low or too high will reduce the ability to accumulate tannins in tea buds.
Similar to the effect of rainfall, tea plants also need a period of cold and low temperature to stop growing and complete the annual reproductive cycle. The point of absolute low temperature that plants can tolerate varies by variety, with some varieties being able to tolerate temperatures of -25oC or lower.
Tea trees are native to tropical forests, so they have great shade tolerance, often photosynthesis of tea trees takes place best in scattered light conditions. Direct light in conditions of high air temperature is harmful to the growth and photosynthesis of tea plants. To limit the harmful effects of strong light and high temperature, some tea growing areas have used shade planting (India, Sri Lanka).
Lighting properties (directed or scattered), light intensity have a great influence on growth and quality of tea. Light requirements of tea plants vary depending on the variety and age of the plant:
Large leaf tea varieties have lower light requirements than small leaf tea varieties.
– Young tea plants have lower light requirements than large tea plants.
In the condition of balanced nutrition and appropriate temperature and humidity factors, a long day of light can be the main factor for tea to achieve maximum yield.
Summary: The yield of crops need basis of four factors (Squire, 1985):
– Solar radiation (sunlight) received (S),
– The amount of solar radiation absorbed by the canopy (Si),
– Efficiency of converting received radiation into dry matter (e), and
– The fraction of the whole dry matter that is the harvest index (H)
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