Characterization and Classification of Some Alluvium Derived Soils under Different Land Uses in Jorhat District of Assam

A study was conducted in the alluvium-derived soils of Jorhat district of Assam in order to characterize the soils as influenced by different land uses. Four representative soil profiles were collected from rice field (P1), vegetable growing area (P2), tea plantation (P3) and natural forest (P4), and analyzed for morphological and physicochemical properties. The soils were dark brown to brownish yellow in colour with dominant hue of 10YR, value ranging from 3 to 6 and chroma ranging from 2 to 8. The soil texture varied from sandy loam to clayey and the soil structure exhibited a trend of development with soil depth. Presence of argillic horizon was observed in rice soils, while development of cambic sub-surface horizon was noticed in soils under other land uses. The soils were acidic (pH 4.5 to 5.5) with appreciable amount of exchangeable H+ [0.19 to 1.15 cmol(p+)kg-1] and Al3+ [0.41 to 2.10 cmol(p+)kg-1]. The process of acidification was not severe in rice soils showing profile weighted mean value of pH 5.3 compared to soils under other land uses (4.6 to 4.7). Surface horizons of all the soils contained higher amount of organic carbon (7.6 to 20.6 g kg-1) and exhibited a regular decreasing pattern with depth. Exch. Ca2+ was the dominant basic cation [1.17 to 3.21 cmol(p+)kg-1] in all the land uses. Rice soils recorded the highest total exchangeable cations, CEC and ECEC [profile weighted means 3.99, 9.6 and 5.25 cmol(p+)kg-1, respectively]. The base saturation was high in the soils under cultivation (weighted mean 41.6 and 34.8% in rice and vegetable growing areas, respectively) followed by forest (30.9%) and tea plantation (30.0%). The soils were classified as Oxyaquic Hapludalf (P1) and Typic Dystrudepts (P2, P3 and P4) at sub-group level.