Characteristics of tea growing soils in relation to soil acidity in upper Brahmaputra Valley of Assam

Abstract

Six typical pedons collected from Dahingapar (P1), Kotalgorie (P2), Baideha (P3), Neghareting (P4), Chenijan (P5) Tea Estates of Jorhat district and Thurajan Tea Estate (P6) of Golaghat district, representing gently to moderately sloping upland in upper Brahmaputra valley of Assam were studied for their characteristics in relation to soil acidity. The soils were deep to very deep, well to moderately well drained, light yellowish brown to light brownish gray, mostly light in texture (except P6), very strongly to strongly acidic and medium to high in organic matter content. The cation exchange capacity (CEC) of soil ranged from 4.5 to 13.2 cmol(p+) kg−1 and the clay CEC ranged from18 to 41 cmol(p+) kg−1 indicating the heterogeneity of mineralogical composition of clays. The increase in clay content with soil depth and presence of thin patchy clay skins in the sub-surface horizons of P4 and P6 indicated presence of argillic horizons. The soils were classified as Typic Dystrudepts (P1, P3 and P5), Fluventic Dystrudepts (P2), Ultic Hapludalfs (P4) and Typic Hapludults (P6). The exchangeable acidity ranged from 0.79 to 7.61 cmol(p+) kg−1 and was mostly constituted by exchangeable Al3+. Aluminium saturation varied from 11.7 to 82.9% in the soils. Aluminium saturation was more than 50% in the sub-surface horizons of most of the soils except in P2. The total potential acidity of the soil varied from 3.6 to 20.7 cmol(p+) kg−1. The pH dependent acidity of the soils varied from 1.77 to 18.87 cmol(p+) kg−1. The pH dependent acidity contributed 18.8 to 91.2% of the total potential acidity.