Pedological Assessment of Soil Organic Carbon and Total Nitrogen Contents in Wetland Rice Ecosystems of Majuli River Island, Assam, India

Abstract

The study of soil organic carbon and total nitrogen in relation to texture, landforms, and soil pH in riverine rice growing wetlands is very important for both agrarian economy and land use related issues in Majuli island of Upper Brahmaputra valley, Assam. Thus, thirteen soil series classified under the subgroups of Inceptisols and Entisols under different alluvial landforms in Majuli river island were selected to investigate the distribution of organic carbon (OC) and Total nitrogen (Total N) in pedological point of view. Our results showed an enrichment in OC and Total N on superficial Ap horizons (silt loam to silty clay loam) to the detriment of the deep sandy C horizons. Nevertheless, the irregular distribution of OC and total N contents with depth in stratified soils of the Island showed differential rates of leaching and its subsequent accumulations due to depositional episodes during seasonal floods in the region. These soils are slightly acid to neutral with mean densities of 30.49 Mg / ha of OC in Majuli series (P5) to 196.78 Mg / ha in Dakshinpat series (P7) with significant variations between the horizons (F=5.904). The data further shows that silty clay texture have mean SOC of 25.24 + -10.48 Mg / ha but low with value of 6.26 2.81 Mg / ha for sand texture whereas total N stocks were high for sand (mean 4.71 + -3.45 Mg / ha). The stratification of Total N and its stocks are highly variable having positive relation with cation exchange capacity (R2=0.57 * * ) and Clay (R2=0.35 * ). The mean C / N ratio of soils was 8.3 + -10.33 but highly variable (Cv of 124%). The regional study shows that geographically explicit information on soil carbon and total N pools must be combined with seasonal flooding history and depositional episodes for better rice management factors in the island.