Traditional Approach

Several attempts have been made to classify the land area into climatic regions. Many of the earlier efforts to delineate agro-climates used manual overlay of isolines representing either potential evapotranspiration or temperature or their combinations and superimposed on soil resource maps. Carter (1954) divided India into six climatic regions, ranging from arid to per humid, based on the criteria of Thornthwaite system of climate classification. Sehgal et al. (1987) prepared a computerized bio-climatic map of NW India, based on the criteria of dry month. Krishnan (1988) delineated 40 soil climatic zones based on major soil types and moisture index. Murthy and Pandey (1978) brought out a 8 agro-ecological region map of India on the basis of physiography, climate, soils and agricultural regions. The approach depicts a good beginning of agro-ecological zoning in the country, but it suffers from several limitations due to over generalizations such as grouping together the areas having different physiography, temperature and soil in zone.

Subramanian (1983) based on the data of 160 meteorological stations in the country and using the concept of moisture adequacy index, delineated 29 agro-ecological zones with the possible 36 combinations of IMA and dominated soil groups as per FAO/UNESCO Soil Map (1974).The planning commission, as a result of mid-term appraisal of the planning targets of VII Plan (1985-1990), divided the country into 15 broad agro-climatic zones based on physiography and climate (Sehgal et al., 1992).

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