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SUMMARY Six noncalcareous pedons from the basaltic terrain of the Western Ghats in Maharashtra, India, were identified for the present study. Of these, two red‐soil pedons (Typic Haplustalfs) and one black‐soil pedon (Vertic Ustropept) are from the Bhimashankar plateau at an elevation of 1000 m above mean sea level, experiencing a humid (>5000 mm rainfall) tropical climate. The other three pedons of black soils (Typic Chromusterts and Typic Ustropept) are from the semi‐arid zone (500–1000 mm rainfall), at an elevation of 825–893 m. Clay mineralogical investigation indicated that interstratified smectite‐kaolin (Sm/K) is dominant in red soils whereas smectite is dominant in black soils. The Sm/K is formed by the transformation of montmorillonite, the first weathering product of Deccan basalts in a humid tropical climate. We suggest that the interstratification of kaolin with chloritized smectite may also be an important ephemeral stage during the transformation of smectite to kaolinite. The presence of zeolites provided sufficient bases to prevent the complete transformation of Sm/K to kaolinite. The presence of smectites and zeolites made the formation of black soils possible in microdepressions even in a tropical humid climate. The genesis of Sm/K and smectite in red and black soils, respectively, suggests that these soils formed through a progressive landscape reduction process. The presence of both Sm/K and smectite in black soil clays of semi‐arid climate suggests that the smectite of these soils was formed in an earlier humid climate.

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Bound by the Himalaya in the north and the Craton in the south, the Indo-Gangetic Plains (IGP) is one of the largest fluvial plains of the world. The IGP is monotonously flat with a spread of surface soils in hot arid conditions of Rajasthan in west to per-humid conditions in West Bengal. The soil-geomorphology of the IGP detailed during the last few decades is useful in determining the interrelationship among the pedogenesis, the climate, and the landscape evolution during the Holocene. These studies demonstrate that the IGP soils developed on five geomorphic surfaces with varying degree of development. Soils occurring on older geomorphic surfaces (N2.5 ka) are polygenetic with a distinct record of climatic changes and neotectonics. The present synthesis is based on recent developments in pedology achieved through macro-and micromorphology, clay mineralogy, pedogenic calcrete, and polygenetic pedogenic features of the IGP soils. A critical evaluation of the IGP soils has helped to comprehend the subtle nuances of the pedogenic processes that were also influenced by anthropogenic activities and cultivation over this vast agricultural tract during the Holocene. We provide state-of-the-art information on the pedology, polygenesis, and soil degradation (natural and anthropogenic) over the last 10 ka. The review has potential as a reference for critical assessment of the pedosphere for health and quality in different parts of the world. In addition, it facilitates developing a suitable management practices for the food security in the 21st century.

Papua New Guinea (PNG) is saddled with frequent natural disasters like earthquake, volcanic eruption, landslide, drought, flood etc. Flood, as a hydrological disaster to humankind's niche brings about a powerful and often sudden, pernicious change in the surface distribution of water on land, while the benevolence of flood manifests in restoring the health of the thalweg from excessive siltation by redistributing the fertile sediments on the riverine floodplains. In respect to social, economic and environmental perspective, flood is one of the most devastating disasters in PNG. This research was conducted to investigate the usefulness of remote sensing, geographic information system and the frequency ratio (FR) for flood susceptibility mapping. FR model was used to handle different independent variables via weighted-based bivariate probability values to generate a plausible flood susceptibility map. This study was conducted in the Markham riverine precinct under Morobe province in PNG. A historical flood inventory database of PNG resource information system (PNGRIS) was used to generate 143 flood locations based on "create fishnet" analysis. 100 (70%) flood sample locations were selected randomly for model building. Ten independent variables, namely land use/land cover, elevation, slope, topographic wetness index, surface runoff, landform, lithology, distance from the main river, soil texture and soil drainage were used into the FR model for flood vulnerability analysis. Finally, the database was developed for areas vulnerable to flood. The result demonstrated a span of FR values ranging from 2.66 (least flood prone) to 19.02 (most flood prone) for the study area. The developed database was reclassified into five (5) flood vulnerability zones segmenting on the FR values, namely very low (less that 5.0), low (5.0-7.5), moderate (7.5-10.0), high (10.0-12.5) and very high susceptibility (more than 12.5). The result indicated that about 19.4% land area as 'very high' and 35.8% as 'high' flood vulnerable class. The FR model output was validated with remaining 43 (30%) flood points, where 42 points were marked as correct predictions which evinced an accuracy of 97.7% in prediction. A total of 137292 people are living in those vulnerable zones. The flood susceptibility analysis using this model will be very useful and also an efficient tool to the local government administrators, researchers and planners for devising flood mitigation plans.

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Micromorphological studies were performed in order to understand the factors and processes involved in the formation of calcium carbonate (CaCO3) in twenty three soil series of Vertisols representing sub-humid, semi-arid and arid climatic regions of Peninsular India. The study indicates that Vertisols contain both pedogenic calcium carbonate (PC) and non-pedogenic calcium carbonate (NPC) irrespective of the ecosystems to which they belong. The NPCs are part of the parent material of Vertisols. Dissolution of NPCs and recrystallization of dissolved Ca2+ ions are responsible for the formation of PCs. Vertisols of arid and semi-arid climates contain more PC in their soil control section (SCS) than those of sub-humid climates. Formation of PC is the prime chemical reaction responsible for the increase in pH, the decrease in the Ca/Mg ratio of exchange site with depth and in the development of subsoil sodicity. Petrographic and scanning electron microscopic (SEM) examination of quartz, feldspars and micas indicate little or no alteration, discounting the possibile formation of smectite during Vertisol formation. X-ray diffraction (XRD) analysis of clays indicates that smectites of Vertisols are fairly well crystallized and do not show any sign of transformation except for hydroxy interlayering. The preservation of the crystallinity of smectite and the lack of transformation of primary minerals thus validate the hypothesis of positive entropy change during the formation of Vertisols.The precise cause-effect relationship between CaCO3 of pedogenic and non-pedogenic origin, and exchangeable Mg, Na and Ca percentages (EMP, ESP and ECP) has been established in the study. This indicates that impoverishment of Ca2+ ions on the exchange sites of Vertisols needs to be controlled by rehabilitation methods that can replenish Ca2+ ions, and thus the study provides relevant information for future land resource management programmes not only on Vertisols of India but also on similar soils occurring elsewhere.

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