Water Management in Horticultural Crops (1+1)

2.Transpiration

• Transpiration is the process by which plants loss water in vapour form into the air through their aerial parts, mainly leaves. It involves nearly 99 per cent of the volume of water absorbed by young plants.
• Usually about 95 per cent of the water absorbed is transpired and only about 5 per cent is used by the plant for metabolic purpose and making the body weight.
• About 90 to 95 per cent of transpiration occurs during the day time and 5 to 10 percent during the night time. Pineapple which is a Crassulacean acid metabolism (CAM) plant is the exception in which most of the stomata remain open during the night time and the major transpiration takes place at night.
• Transpiration rate in the morning is less. It increases with the increase in temperature during the day time and reaches the maximum at around 2 pm local time.
• Transpiration is usually expressed by transpiration ratio or transpiration coefficient that refers to the volume of water transpired by a plant to produce a unit quantity of dry matter.
• The factors affecting absorption also affect transpiration, besides the chemical and cultural factors.