Pedogenic characterization of soils of Eastern Region of the Brahmaputra Valley, Assam

An investigation was carried out in the alluvium derived soils of Eastern part of the Brahmaputra valley comprising two agro-climatic zones (Upper Brahmaputra valley zone and North bank plain zone) to characterize and classify the soils in the year 2023-2024. In total, five soil profiles were exposed from each zone (P1-P5 in UBVZ) and (P6-P10 in NBPZ) with a total number of 55 soil samples, collected from the ten profiles which were analyzed for morphological and physicochemical properties. Distinct variation was observed in the both morphological and physicochemical properties between the soils of UBVZ and NBPZ. The colour of the soils was dark brown to brownish yellow with a dominant hue of 10YR, with a value ranging from 4-6 and the chroma lying in the range of 2-5.The soil texture was mostly loam to clay loam in UBVZ and loamy sand to sandy loam in NBPZ. The soil structure was found to be medium to firm and weak sub angular blocky throughout all the profiles. The surface horizons pertained considerable higher amount of SOC (0.08-1.61%), maintaining a steady reduction down the profile. The soils were extremely to moderately acidic (pH 4.20-5.92) with a substantial amount of Ex. H⁺ and Ex Al³⁺ [0.08-0.89 and 0.74-2.11 cmol (P⁺) kg^-1] respectively. The overall dominance of the concentration of exchangeable cations were as follows; Ca²⁺>Mg²⁺>Na⁺=K⁺. The CEC of the soils varied from 4.2-11.4 cmol (P⁺) kg^-1. The content of basic cations was higher in soils of UBVZ compared to NBPZ thereby leading to higher PBS in UBVZ. The crystalline form of Fe oxides extracted by Na dithionite (Fed) was highest (0.37% to 3.02%) among all the fractions of other pedogenic oxides of Fe and Al, with a higher amount in UBVZ. The soils of UBVZ were mostly classified as Inceptisols except one profile (P2) while Entisols dominated the NBPZ.