Agricultural Meteorology in India

Abstract

THE annual report of the Agricultural Meteorology Section, India Meteorological Department, for the year 1939-40 covers the last year during which the section was being financed by the Imperial Council of Agricultural Research, the Government of India having taken over the Section from April 1, 1940. The report describes a number of investigations, most of them concerned with the micro-climatology of crops, that is, with the climates experienced within growing crops, as distinct from the more artificial climate of the ordinary meteorological instrument enclosure which is of greater interest for comparisons between the climates of different countries. A number of new instruments have been developed, including several forms of portable but accurate galvanometer for use with thermocouples of copper and constantan for the measurement of temperature in micro-climatology. The recently completed 35-ft. tower at the Central Agricultural Meteorological Observatory at Poona has been found very useful for mounting thermographs, hygrometers and anemometers, for studies of the variations of temperature, humidity and wind with height, which are important in the control of the vertical exchange of heat and moisture between the soil and the overlying air. At Poona, insolation even in January is found to be so strong that the convective layer, with temperature decreasing with height, does not normally disappear during the night, and is generally still to be observed as a layer one or two feet thick at 6 a.m., when temperature in the lower layers is near its minimum. At that time it is generally coldest at a height of one or two feet, with temperature increasing upwards from that level for several hundred feet, the rise amounting already to about 3° C. on reaching the top of the 35-ft. tower. By April the greater insolation is more than counteracted in its tendency to maintain the convective layer by the effect of a higher average nocturnal wind speed, the net result being that the layer has almost disappeared by 6 a.m. The report includes a number of other studies relating to micro-climatology, among which is a table showing the average wind speed in the afternoon at various heights up to 8 ft. in eight different crops, expressed as a percentage of the wind at the same height above open ground. Up to 2 ft., wheat and sugar cane show the highest degree of sheltering, tobacco and suran the least.