Dutta, SamironBora, Denim2023-10-262023-10-262021https://krishikosh.egranth.ac.in/handle/1/5810199709The present investigation was carried out to study the distribution of Arsenic in relation to the pedogenesis of rice growing soils of Titabar circle of Jorhat district and to assess its bioavailability. To accomplish the objectives four locations (Nangal Gaon, Bosa Gaon, LahongBebejia, and Sologuri) were selected covering the entire circle and a soil profile was exposed in each location. In addition to the soil samples collected from eighteen numbers of horizons of four profiles, five numbers of composite surface soil samples (0-20 cm) and equal numbers of groundwater and rice plant samples were also collected from each location. The soils were gray to brownish-yellow in colour and varied widely in texture (sandy loam to silty clay), sand content (12.8 – 63.8%), silt (17.6-50.8%), clay (15.8-46.6%), and OC (0.38 – 0.91%). Soil structure was mostly sub-angular blocky with massive at the surface. Soils were strongly to medium acidic in reaction (pH 5.15-5.83) with low CEC (7.5-9.7) and base saturation (36.3 – 48.3%). Based on the morphological and Physico-chemical properties, the soils of P1(Nangal Gaon) and P3 (Lahong Bebejia) were classified as Typic Endoaquepts and Aquic Dystrudepts respectively. The soils of both P2 (BosaGaon), and P4 (Sologuri) were classified as Oxyaquic Dystrudepts. The crystalline Fe and Al fractions of the soils varied from 1.17-2.11% and 0.37-0.82% respectively. The content of amorphous Fe and Al fractions was low with a range from 0.32-0.76% and 0.18-0.54% respectively. The P2 (BosaGaon) was recorded for the highest weighted mean of all the forms of Fe and Al. Considerable variation was observed in the total As content of the soils which ranged from 11.18 to 20.75 mg kg-1. The highest weighted mean of total As was measured in P4 (20.22 mg kg-1) followed by P2 (17.48 mg kg-1), P1 (14.54 mg kg-1), and P3 (13.65 mg kg-1). The distribution of total As in the soil profiles was found to be mostly influenced by the particle size fractions and different forms of Fe and Al. Thus As in these soils can be considered geogenic in origin as it was found to be regulated by the soil properties inherited from the parent material. The bioavailability of As was evaluated through fractionation of soil As by the sequential extraction method. The content of (NH4)2SO4, NH4H2PO4, NH4-Oxalate Buffer, NH4-Oxalate buffer with Ascorbic Acid, and residual As in the soils were ranged from 0.27-0.49 mg kg-1, 0.67-1.61 mg kg-1, 2.94-6.15 mg kg-1, 2.38-4.47 mg kg-1 and 1.16-3.17 mg kg-1 respectively. Among all the fractions As bound to amorphous materials (NH4-Oxalate Buffer) was found to be the most dominant fraction followed by As bound to crystalline compounds (NH4-Oxalate buffer with Ascorbic Acid), residual fraction, the specifically adsorbed fraction (NH4H2PO4,) and readily soluble fraction ((NH4)2SO4). Similar to total As, the different fractions of soil As were also found to be influenced by the particle size fractions and different forms of Fe and Al. A highly dynamic relationship was observed among all the As fractions in the studied soils indicated a strong replenishment mechanism. The total As content determined in the composite surface soil samples was varied from 10.27-17.52 mg kg-1and it was significantly higher in soils of Nagal gaon (14.92 mg kg-1) and Bosagaon area (15.29 mg kg-1) than Lohong Babejia (11.39 mg kg-1) and Sologuri area (11.63 mg kg-1). The content of As in groundwater and rice grain were varied from 101.5 -221.6 μg L-1 and 0.517-0.966mg kg-1 respectively. Significantly the highest groundwater concentration of As was measured in Sologuri (216.4 μg L-1) followed by Bosa gaon (120.9 μg L-1), Lohong Bebejia (112.6 μg L-1), and Nangal gaon area (103.1 μg L-1). The groundwater As content showed a significant negative relationship with the total As content of soils but maintained a highly positive relationship with As content of rice grains. The groundwater and rice grain As content did not show any relationship with the fractions of As in A horizon but showed a highly positive relationship with F2, F3, F5, and total As of B horizon. The path diagram indicated the maximum contribution of specifically adsorbed As fraction (F2) towards the readily soluble fraction of As followed by crystalline (F4) and residual fraction (F5).EnglishThesis