Red ferruginous soils of tropical Indian environments: A review of the pedogenic processes and its implications for edaphology

Abstract

Red ferruginous (RF) soils of tropical Indian environments belong to Entisols, Inceptisols, Alfisols, Mollisols and Ultisols soil orders. The occurrence of Ultisols alongside acidic Alfisols and Mollisols in both zeolitic and nonzeolitic parent materials in humid tropical (HT) climatic environments, indicates that the soil diversity in India is large. These soils are not confined to a single production system and generally maintain a positive organic carbon (OC) balance without adding significantly to greenhouse gas emissions. This review presents a synthesis of literature on the recent developments on the pedology of RF soils, including their physical, chemical, biological, mineralogical and micro-morphological properties, and their degradation status. It also addresses the changes in soil properties in semi-arid tropical (SAT) areas, created by climate shift during the Holocene. This knowledge contributed to our understanding as to how the parent material composition influences the formation of Alfisols, Mollisols and Ultisols in weathering environments of HT climate; and also as to how the relict Alfisols of SAT areas are polygenetic. The state-of-the-art information developed through the extensive work on such soils has helped establish an organic link between pedogenetic processes and bulk soil properties, and has provided an insight of many pedological and edaphological issues related to Alfisols, Mollisols and Ultisols mainly of HT climate. The synthesis has helped us to understand as to why the formation of Oxisols from Ultisols is an improbable genetic pathway in tropical environment of India and elsewhere in the world. There is a strong need to modify the mineralogy class of highly weathered RF soils. We hope this review will help to dispel some of the myths on the formation of tropical soils and their low fertility by putting in context their characteristics and capacity to be productive.

Natural Chemical Degradation of Soils in the Indian Semi-Arid Tropics and Remedial Measures

“…It was, however, envisaged that if adverse changes occur in some areas, then these processes will certainly constitute a most serious form of humaninduced degradation of natural resources. Climate change from the humid to semi-arid did occur during the late Holocene in major parts of the Indian subcontinent [3][4][5] . It is quite likely, therefore, that the current aridic environment prevailing in many parts of the world, including India, might create adverse physical and chemical environment, leading to reduced productivity of soils.…”

“…There is no dearth of literature on soil degradation due to anthropogenic activities [9][10][11][12][13] . But a precise account of factors of natural chemical degradation in major soil types of India forms a robust database for reference [3][4][5]25 to expand the present knowledge on natural soil degradation and to protect the livelihood of humankind.…”

“…The formation of PC in the arid climate enhances the pH and also the relative abundance of Na + ions on soil exchange sites and in the solution; and the Na + ions in turn cause dispersion of the fine clay particles. The dispersed fine clays translocate in major soil types of India [3][4][5] as the formation of PC creates a Na + -enriched chemical environment conducive for the deflocculation of clay particles and their subsequent movement downward. Therefore, the formation of PC and the clay illuviation are two concurrent and contemporary pedogenetic events, resulting in increase in relative proportion of sodium, causing increased sodium adsorption 25 ).…”

“…These pedogenetic processes continue to represent a pedogenic threshold during the dry climates of the Holocene [3][4][5] . Thus the formation of PC is a basic natural degradation process 1 , induced by tectonics-climate linked events 17,25,30 , which exhibits the regressive pedogenesis 6 which also immobilizes C in unavailable form.…”

“…Moreover the rain-fed agriculture in the SAT area is fragile in view of spatial and temporal variation of rainfall. Besides, the rainfall is of high intensity and during a short duration, which causes severe soil erosion, leading to physical, chemical and biological degradation of soils 1,[3][4][5] . This basic fact has made scientists, agriculturists, environmentalists and policy makers anxious whether the soil resource base will be able to feed the expected 8.2 billion world population by 2030 (www.unpopulation.org).…”