Micromorphological Studies of Soils of Indo-Gangetic Alluvial Plain Developed under Different Climatic Conditions

Micromorphological features of four soil pedons from north-western part of India with 1165, 946, 837 and 426 mm of rainfall, having similar physiography and age were studied. The primary birefringent clay cutans and matrans increased with the increase in the amount of rainfall. Pedon with 1165 mm rainfall had well developed clay skins to qualify it for argillic horizon and those with 946 and 837 mm rainfall also showed clay cutans but not sufficient to qualify for argillic horizon. Pedon with 426 mm rainfall lacked the clay cutans due to low rainfall, presence of calcium carbonate and high biological activity. Several features of calcium carbonate accumulation, such as calcitans, neocalcitans nodules, lubblinites etc., were also related to precipitation. The in situ weathered mica grains were observed in all the pedons. An attempt has been made to redefine the argillic horizon based on micromorphological studies. A 4% value of illuviated clay helps bettter discrimination for argillic horizon at 40x magnification.