Wind velocity and its effect on crop production
Air in horizontal motion is known as wind. Vertical movement is noticed but negligibly small compared to horizontal movement as the height of the atmosphere is only for few km. However vertical movement or uplift of air only causes significant weather changes in cloud formation and rain. The velocity of wind at a place depends on various factors such as geographical situation, topography, altitude, distance from seashore, flat plains, vegetation etc. Wind affects crop growth mechanically (directly) and physiologically (indirect).
Wind speed in different seasons
Winds represent air in motion. The primary cause of all winds is regional differences in temperature, producing regional differences in pressure. When these pressure differences persist for several hours, the rotation of the earth modifies the direction of motion, till the winds blow along lines of equal pressure. Wind direction and speed are modified frequently due to seasonal variation in solar radiation and differential heating of the earth’s surface.
1. Wind speed: The winds are generally measured over level, open terrain at 3 metres about ground. Yet, a general idea of the distribution of the mean daily wind speed, on an annual basis as well as on a monthly basis, would be useful. The mean daily wind speed is the value obtained by averaging the wind speed (irrespective of direction) for a whole day. This averaged for all the days of a month is the mean daily wind speed for that month. The daily values averaged for all the 365 days of the year is the annual mean daily wind speed.
2. Wind Direction: Winds are always named after the direction they come from. Thus, a wind from the south, blowing towards north is called south wind. The wind vane is an instrument used to find out the direction of the wind. Windward refers to the direction wind comes from, and leeward refers to the direction it blows to. When a wind blows more frequently from one direction than from any other, it is called a prevailing wind.
3. South West Monsoon wind direction: During South West Monsoon period of June to September, the westerly winds prevail on the west of Kerala and south winds on the west of northern Circars, Orissa and Bengal. During April and May the region of high temperature is shifted to north viz., upper Sind, lower Punjab and Western Rajasthan. This area becomes the minimum barometric pressure area to which monsoon winds are directed.
4. North East Monsoon wind direction: During North East Monsoon period of October to December, on account of the increase in barometric pressure in Northern India, there is a shift in the barometric pressure to the South East and North Easterly winds begin to flow on the eastern coast, by the end of September. These changes bring on heavy and continue rainfall to the Southern and South Eastern India.
(a) Mechanical effects
• Wind causes mechanical lacerations and bruises on the tissues of crop plants,
• Violent winds causes lodging of crop plants such as wheat, maize, sugarcane, rice etc.,
• A very high velocity of wind (gale, blizzard, hurricane, cyclone etc., breaks dead and living branches of trees and even uproots them completely,
• In bare deserts, high velocity of wind causes constant soil erosion and this makes it difficult for plants to grow,
• Wind has a powerful effect on the humidity of atmosphere.
(b) Physiological effects
• Wind increases the rate of transpiration in plants.
• Hot dry winds causes much damage to crops at the time of flowering.
• The internal water balance of plants is affected resulting in poor seed setting.
• Another form of damage in blossom injury caused by evaporation of secretions from the stigmas.
(c) Beneficial effects
• Wind is also responsible for causing rainfall to a very large extent. In India the monsoon type of rainfall is largely determined by particular patterns of wind movement. (Trade winds)
• Wind helps in pollination of flowers and dispersal of seed, fruits and microorganisms.
• The hot, dry wind may reduce the incidence of dangerous yellow rust of wheat.
• Moderate wind has a beneficial effect on photosynthesis by continuously replacing the carbon dioxide absorbed by the leaf surfaces.
(d) Remedy
Velocity of wind can be reduced by growing tall, sturdy trees across the direction of the wind as wind breaks. To arrest the movement of soil by wind erosion shelterbelts of vegetation are raised.
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