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Subject: Soil Sciences × Author: Mohanty, Shraddha × End date: 2018 × Start date: 2018 × Type: Thesis ×
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    ThesisItemOpen Access
    PEDOGENIC CHARACTERIZATION OF PADDY AND ASSOCIATED NON-PADDY SOILS OF ASSAM
    (AAU, Jorhat, 2018) Mohanty, Shraddha; Karmakar, Rajendra Mohan
    An investigation was carried out to study the morphological, physical and chemical characteristics, clay-organic carbon complexes and pedogenic distribution of iron, manganese and aluminium in clay fraction of paddy and associated non-paddy soils of Assam. Four districts viz., Golaghat, Jorhat, Sivasagar and Dibrugarh in the Upper Brahmaputra valley of Assam were selected for the present study. Eight soil profiles four each from mono-cropped paddy and associated non-paddy areas were collected. Horizon-wise soil samples were analyzed for important soil properties and clay-organic carbon complexes and different forms of Fe, Al, Mn in clay fraction using standard procedures. Soil colour varied from dark gray to brownish yellow. Yellow (10YR 6/8) to light red (2.5YR 6/8) mottles were observed in the subsurface horizons of the soils. Texture of the soils ranged from loamy sand to clay and structure varied from massive to subangular blocky. Sand, silt and clay contents varied from 11.3-49.0, 21.5-50.8 and 26.2-56.9 per cent in paddy and 23.3-65.4, 11.4-42.9 and 14.4-44.4 per cent in non-paddy soils respectively. Organic carbon content in soil varied from 2.0-12.0 and 0.5-10.0 g kg-1 in paddy and non-paddy soils respectively. Bulk density of soils increased with soil depth, pH of the soils varied from 4.4-6.0 and EC was found to be low (0.11-0.20 dSm-1). CEC of soil varied from 7.5-14.1 cmol (p+) kg-1 in paddy and 5.1-12.7 cmol (p+) kg-1 in non-paddy soils having dominance of exch. Ca++ followed by Mg++, Na+ and K+. Base saturation of the soil was low (32.3 to 57.5%). Soils were classified as: Typic Epiaqualfs (P1), Aeric Epiaqualfs (NP1, P2, P3, NP3, P4), Ultic Hapludalfs (NP2) and Typic Dystrudepts (NP4). Clay-organic carbon complex (OCclay) varied from 2.41-15.5 g kg-1 in paddy soils and 0.71-13.80 g kg-1 in non-paddy soils. Results showed that OCclay constituted 37.18-65.60% of SOC in paddy soils and 31.60-54.62% of SOC in non-paddy soils. Humus C (CH-clay), humin C (CHN-clay) in the clay fraction was found to be higher in non-paddy soils, whereas humic acid C (CHA-clay) and fulvic acid C (CFA-clay) in clay fraction was higher in paddy soils than their counter parts. CHA-clay/CFA-clay ratio was observed to be less than 1 indicating dominance of fulvic acid in the clay-organic carbon complexes. 25 Total (Fet), dithionite extractable (Fed), pyrophosphate extractable iron (Fep) and manganese in clay fraction were slightly higher in non-paddy soils as compared to paddy soils whereas oxalate extractable iron and manganese showed a reverse trend. Fed formed major portion of total iron content in clay fraction (Fet) followed by Feo and Fep in both paddy and non-paddy soils. Crystalline iron oxide (Fed-Feo) and silicate iron (Fet-Fed) in clay fraction was found to be higher in non-paddy soils while amorphous inorganic form of iron (Feo-Fep) showed the reverse trend. Different forms of Mn showed similar trend as that of different forms of iron in clay fraction of both paddy and associated non-paddy soils. Total Al (Alt), dithionite extractable Al (Ald) and oxalate extractable Al (Alo) in clay fraction were slightly higher in paddy soils as compared to non-paddy soils whereas pyrophosphate extractable Al (Alp) showed a reverse trend. Ald formed major portion of total Al content in clay fraction (Alt) followed by Alp and Alo in both paddy and non-paddy soils. Crystalline Al oxide (Ald-Alo), amorphous inorganic Al (Alo-Alp) and silicate Al (Alt-Ald) in clay fraction was found to be higher in paddy soils than non-paddy soils. In the present investigation, variation in morphological, physical and chemical characteristics of soils, clay organic carbon fractions, distribution of various forms of Fe, Mn and Al in clay fraction were observed in the paddy and associated non-paddy soils of Assam. Low amount of sand and high amount of clay in paddy soils as compared to non-paddy soils indicate more intense weathering in paddy soils due to anthropogenic factors and agro-hydrological regimes. Most of the paddy soils exhibited aquic characteristics leading to process of gleization. Formation of more amounts of clay-organic complexes was also observed in the paddy soils. Further studies are needed using modern tools (SEM, IR, X-ray etc.) for detailed pedogenesis and mechanisms in clay-organic complex formation in paddy and associated non-paddy soils of Assam.