Genesis of lime nodules in vertisols of Rajasthan

Genesis of lime nodules was studied in six soil series of Vertisols. Among the selected soil series, Taswaria, Taswaria sodic and Bhatewar were derived from calcic-gneiss complex, whereas Chambal, Aklera and Patan series were developed on basaltic complex. Very pale brown to light grey, embraced in soft powdery lime, bigger size, irregular outlined, siliceous, alkali and alkaline earth oxides rich nodules formed the zone of lime accumulations below the depth of 60–100 cm in the formers, while grey, smaller size, rounded sesquioxide rich nodules were interspersed in the soils below the depth of 90–110 cm in the latter. Lime nodules in Taswaria, Taswaria sodic and Bhatewar series were developed from the precipitation Ca²⁺, Mg²⁺ and HCO₃-, liberated as a result of in situ weathering of carbonatic rock, using fragments of calcic gneiss as nuclei. In contrast, nodules with the fragments of basalt as nuclei in Chambal, Aklera and Patan series were developed from the precipitation of Ca²⁺, Mg²⁺ and HCO₃- obtained from weathering of limestone band associated with Vindhyan system and these were rolled down after nodulation with the basaltic alluvium down the slope. The difference in the morphology of nodules was attributed to the material encircling them, supply and content of carbonate forming ions for nodulation and the extent of alluviation