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).