Morphological Properties of Red and Black Soils of Selected Benchmark Spots in Semi-Arid Tropics of India

Morphological properties of red and black soils are described. Soil depth, color, texture, consistence, structure, roots, coarse fragments, nodules, effervescence, slickensides, cracks and clay cutans are described in subhumid (moist and dry), semi-arid (moist, dry) and arid ecosystems.Soils under high management are darker in color indicating more soil organic carbon content. Wet consistence such as very sticky and very plastic corresponds with those horizons in black soils showing well developed slickensides. Firm moist consistence may indicate development of sodicity problems provided there are no or very less amount of soil modifiers such as zeolites and gypsum. Higher root density in soils corresponds with lower degree of CaCO3 content as indicated by slight effervescence with dilute HCl in the field. Black soils contained coarse fragments of 3-8%, 1-10%, 1-10% and 5-15% in sub-humid (moist), semi-arid (moist), semi-arid (dry) and arid bioclimatic system, respectively. In general, the degree of effervescence is in line with size and quantity of coarse fragments and calcium concretions observed in the field. In general black soils under high management show slickensides at lower depths. With decrease in mean annual rainfall, the depth of occurrence of slickensides decreases from 60 cm in sub-humid (moist) to 30 cm in semi-arid (dry) bioclimate. Management interventions including irrigation in drier tracts push the slickensides further down in the profile. The formation of Sodic Haplusterts indicate poor organic carbon accumulation but a very high inorganic carbon sequestration in soils of dry part of the arid bioclimatic system. It manifests natural chemical degradation of soils with mean annual rainfall of