S.K. Ray

Lateritic soils of Kerala, India : their mineralogy, genesis, and taxonomy

In this study, we report the chemical and mineralogical characteristics of 4 benchmark Ultisols of Kerala to elucidate their genesis and taxonomy. The taxonomic rationale of the mineralogy class of Ultisols and other highly weathered soils on the basis of the contemporary pedogenesis is also explained. The Ultisols of Kerala have low pH, low cation exchange capacity, low effective cation exchange capacity and base saturation, with dominant presence of 1 : 1 clays and gibbsite. Presence of gibbsite along with 2 : 1 minerals discounts the hypothesis of anti-gibbsite effect. Since the kaolins are interstratified with hydroxy-interlayered vermiculites (HIV), the formation of gibbsite from kaolinite is not tenable. Thus, gibbsite is formed from primary minerals in an earlier alkaline pedo-environment. Therefore, the presence of gibbsite does not necessarily indicate an advanced stage of weathering. On the basis of a dominant amount of gibbsite, a mineralogy class such as allitic or gibbsitic does not establish a legacy between the contemporary pedogenesis and the mineralogy. The dominance of kaolin–HIV in the fine clays of Ultisols and their persistence, possibly since early Tertiary, suggests that ‘steady state’ may exist in soils developed on long-term weathered saprolite. Since the present acid environment of Ultisols does not allow desilication, the chemical transformation of Ultisols to Oxisols with time is difficult to reconcile as envisaged in the traditional model of tropical soil genesis.

Tectonics-climate-linked natural soil degradation and its impact in rainfed agriculture: Indian experience

Soil is the most basic of all resources and the primary substrate for growing crops. It is also non-renewable over the human timescale. This basic fact made all scientists, agriculturists, environmentalists and policy makers anxious about whether soil resources will remain capable to feed, clothe and shelter the expected 8.2 billion inhabitants of the world by the year 2030 (www.unpopulation.org). The available land resources are gradually diminishing because, on a global scale, land resources and population are unevenly distributed. Soils, being most dynamic, are able to supply nutrients, buffer acid and base reactions, destroy and absorb pathogens, detoxify and attenuate xenobiotic and inorganic compounds and have the capacity for self-restoration through soil formation. However, soil formation is a slow process, and a substantial amount of soil can form only over a geologic timescale. Soil misuses and extremes of condition can upset these self-regulating attributes and cause a soil to regress from a higher to a lower type of usefulness and/or drastically diminish its productivity (Lal et al., 1989). This unfavourable endowment of soils has been termed ‘soil degradation’. Definition, Processes and Factors of Soil Degradation