Water balanceWhen the rate of water absorption equal to the rate of transpiration, the guard cells become turgid, carbon dioxide enters rapidly into the leaves, the rate of photosynthesis is high, rate of respiration is normal, assimilation is enough and crop growth rate is maximum. Drought When the water balance becomes negative, the stomatal opening decreases. The rate of photosynthesis and crop growth is also decreased. The effects of drought on determinate crops are greater than on the indeterminate crops. The vegetables crops may be classified into 2 groups in relation to drought: 1.Drought avoidersDrought avoiders avoid the drying of the tissue by maintaining their water uptake and by reducing water loss. The plants may produce more root than shoots. They have ability to move their leaves, develop hairs to insulate the leaf surface and may become waxy. The legume crops are good drought avoiders. 2.Drought toleratorsThe tolerators survive drought by functioning normally even with a low amount of water in their tissues. Vegetable crops cannot sustain prolonged drought stress without loss in yield and quality. 5.Wind Wind aids in dissemination of pollen and reducing frost effect, but it causes contamination, plant lodging and spread of pests and diseases. Wind movement influence the basic plant physiological processes. During rapid growth of plants, carbon dioxide is rapidly depleted on the leaf surface. A slight wind is essential for the supply of carbon dioxide near the plant surface. Wind is a very limiting factor in vegetable production in areas where strong winds frequently occur. A wind break is the structure that reduces the speed of wind. When the trees are used as wind break, they are called shelter belts. All vegetable crops, except the tree vegetables, are very susceptible to wind speeds greater than the ordinary. E.g. the seed production of onion is affected due to windy weather at the bolting stage of the crop in some areas. When there is no wind, the rate of resupplying the surface of the leaf is limited, so entry of CO2is too slow to maintain rapid photosynthesis. Wind also carries O2away from the plant. Less wind leads to less evaporation and less water requirement. The deeper the root system of the crop, generally the more resistant it is to strong winds. Varieties that are early-maturing
21 have a better chance of being harvested before the onset of strong winds than late-maturing ones. Dust and smoke carried by wind reduces the photosynthetic area of crops while the big particles leads to physical injury of vegetable crops. 6. HumidityHumidity plays the most important role in the occurrence of pests and diseases. Certain diseases like powdery mildew are associated with dry weather but humid condition is known to favor diseases like downy mildew and fungal blights affecting foliage. A cool humid place is ideal for growing vegetables such as cabbage, cauliflower, turnip, spinach and beet root especially for seed production. Dry and higher temperature conditions are ideal for seed
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- Winter '17
- PROF CHENJE
- Work, Vegetable, cucurbits, vegetable crops