Division of Soil Science and Agricultural Chemistry, Indian Agricultural Research Institute, New Delhi, 110012.
Present address: 1 Department of Soil Science, Assam Agricultural University, Jorhat, 785013.
Distribution of humic substances was studied in the soils developed on different physiographic units in lower Brahmaputra valley zone of Assam. Major portion of the soil organic carbon remained unhumified in the surface horizon. Fulvic acid constituted the major part (47.6–90.0%) of the humus carbon. Humic acid decreased with soil depth whereas fulvic acid was found to increase in the illuvial horizons of Ruptic-Ultic Dystrochrept on piedmont plain and Typic Hapludult on monadnock. The formation of metal-humus complexes was observed with humic and fulvic acid fractions. But humic acid fraction was found to form more complexes with both Fe and Al.
Humus, C:N ratio, humic acid, fulvic acid, metal-humus complexes
