Introductory Agrometeorology/Wind and Humidity

Objectives of the chapter To understand: causes of wind, wind speed and direction, its measurement and significance in crop production saturation of vapour pressure, determinants of humidity, significance in crop production WIND It is defined as the horizontal movement of air relative to earth surface caused by difference in pressure between two regions. Two types air movements: Vertical Movement of air: called current Horizontal movement of air: called wind. Wind is the essential part of the thermodynamic mechanism of atmosphere, which serves as means of transporting heat, moisture and other properties from one part of the earth to other. Factors affecting wind motion Horizontal Pressure Gradient Coriolis Force Geostrophic Wind Frictional Force Centrifugal action of the Wind Gradient Wind Wind Measurement Anemometer Anemograph Wind vane Beaufort Scale Effect of Wind In Crop -High speed wind, high temperature and high humidity leads to desiccation of crops. -hot and dry wind and low soil moisture (water stress in plant, stunted growth, early maturity) -Heavy Wind:destruct the internal physiology of crops, lodging and shattering of crop, dropping of the pre-mature fruit, interfere pollination which hampers seed formation. -Mild Wind: Good for crops -help in pollination which results good fruit setting -help in agriculture operation (cleaning, winnowing) Humidity water vapor content of air at any time and place Vapor Pressure Saturation deficit Absolute Humidity Specific Humidity Mixing Ratio Relative humidity Dew Point Measurement of Humidity RH is measured by using a. Dry and wet bulb thermometer b. Psychrometers c. Hair Hygrometer Significance of RH in crops Low RH, high temperature, high wind – desiccation, water stress, more ET High humidity – fungal infection, low transpiration High RH + High T - more occurrence of pest and disease incidence Low RH + low T- more occurrence of pest and disease incidence High RH + low T - more occurrence of pest and disease incidence Low humidity – more demand of irrigation Extremely low humidity – plant get wilted and killed Soil moisture Evaporation and Precipitation