Andisols of the Nilgiri highlands: new insight into their classification, age and genesis
Résumé
In India, soils have, for a long time, been classified according to their colour. Nilgiri soils have not escaped this rule and Francis (1908), in the district gazetteer dealing with this region, noticed that ‘four varieties are usually recognised. These are the black, which is a rich loam and the best of all... the brown... the yellow... and the red soil...'. This study focuses exclusively on the ‘black soils' of the Nilgiri Hills. Detailed results regarding their properties, genesis, and classification in modern taxonomies are provided and demonstrate that these soils, which occur on hillslopes and hilltops, are very different from the other ‘black' soils occurring in South India: namely peat soils, which are also found in the Nilgiri Hills but are restricted to valley floors; and Vertisols, which occur on colluvio-alluvial parent material in the Deccan traps as well as portions of the Precambrian basement. Isotopic results bring to light the influence of palaeoecological conditions, particularly the impact of a colder period, characterised by grassland vegetation at the end of the Pleistocene, on the in-situ accumulation of organic matter.
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