STUDIES ON THE DISTRIBUTION OF BORON FORMS IN SOME CULTIVATED SOILS OF HIMACHAL PRADESH
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Date
24-07-18
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CSKHPKV, Palampur
Abstract
Understanding the spatial distribution of various forms of boron in soils helps in predicting its short- and long-term availability for sustainable crop production. In the present investigation, 202 surface soil samples, representing major soils (Alfisols, Entisols & Inceptisols) and land use types were collected from Outer and Lesser Himalayan regions of Himachal Pradesh to study the spatial distribution of B forms vis-à-vis their relationship with important soil properties. The soil samples were collected at 0-15 cm depth from cultivated soils under maize-wheat, paddy-wheat, vegetable-based & sugarcane-based cropping sequences and at 0-30 cm depth from tea gardens & orchards of mango, mandarin, apple etc. and analyzed for important soil properties and B forms using standard methods. The depth-wise distribution of those soil attributes and B forms (at 0-15, 15-30 & 30-60 cm) was also studied in the selected soils. Sand (%), silt (%), clay (%), textural class, soil pH (1:2.5), electrical conductivity (μS cm-1), organic carbon (g kg-1), cation exchange capacity {cmol(p+) kg-1}, base saturation (%) and calcium carbonate (%) in cultivated soils of Himachal Pradesh ranged from 25 to 80, 12 to 45, 6 to 32, loamy sand to clay loam, 5.2 to 7.8 (slightly acid to slightly alkaline), 40 to 372, 2.8 to 22.0, 4.1 to 16.4, 48 to 77 and 0.05 to 2.20, respectively. As regards available nutrient status, soils were medium in available N & K, low in available P & S, high in available Ca & Mg, sufficient in available Cu, Fe & Mn and deficient to sufficient in available Zn and B. Per cent soil samples deficient in N, P, S, Zn and B were 18, 45, 44, 36 and 55, respectively. Such a spatial variation in soil properties and fertility status may be explained in the light of pedo-genesis and prevailing nutrient management practices. Water soluble, exchangeable, specifically adsorbed, oxide occluded, organically bound, residual and total boron in cultivated soils ranged from 0.104 to 0.389, 0.128 to 0.393, 0.215 to 0.680, 0.567 to 2.13, 0.79 to 2.65, 20.04 to 53.16 and 22.0 to 59.14 mg kg-1 with mean values of 0.218, 0.231, 0.402, 1.26, 1.46, 34.09 and 37.67 mg kg-1, respectively. On an average, water soluble, exchangeable, specifically adsorbed, oxide occluded, organically bound and residual B constituted about 0.58, 0.61, 1.07, 3.34, 3.86 and 90.6 per cent of total B, respectively. As regards depth-wise distribution, surface soils were found rich in available and potentially available reserves of B as compared to sub-surface soils. Irrespective of land use types and soils, there were significant and positive correlations between different chemical pools of B, indicating the existence of dynamic equilibrium among them. Among all soil properties, clay, organic carbon and cation exchange capacity exhibited better correlations with each form of B. The step-wise multiple regression analysis showed that organic carbon contributed largely to different pools of boron. Soils deficient in available B had lower content of each form of B as compared to those, sufficient in available B. Further, soils with lower values of clay, organic carbon and cation exchange capacity contained less amount of soil B in each pool as compared to soils higher in these soil attributes. Therefore, former soils require relatively more attention on B mangement as compared to latter ones for sustaining soil productivity.
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