DISTRIBUTION OF BORON IN SOME IDENTIFIED SOILS AND LAND USE SYSTEMS OF KARNATAKA
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Date
40865
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University of Agricultural Sciences GKVK, Bangalore
Abstract
A study was conducted with the objectives of determination of plant available
boron content in major soil types and cropping systems of Karnataka, to quantify the
chemical fractions of boron and to study their adsorption behaviour. For assessing
available boron status in soils of Karnataka, samples were drawn from the dominant soils
representing the map units of 1:250,000 scale Soil Map of Karnataka State. For the
studies chemical fractions of boron in soils and adsorption behaviour, soil samples have
been collected from different agroclimatic zones of Karnataka representing major soils
and cropping systems: Northern dry zone, Central dry zone, Eastern dry zone, Southern
dry zone, Southern transitional zone, Northern transitional zone, Hilly zone and Coastal
zone. Northern dry zone recorded higher soil available boron (1.55 mg kg-1soil) and
Coastal zone least (0.01 mg kg-1soil) and for others boron content ranged from 0.11 mg
kg-1 soil to 1.09 mg kg-1soil. Deficiency of available boron was noticed in Coastal and
Hill ecosystems experiencing of high rainfall. Among the chemical fractions, residual
boron contributed around 98 per cent. Other fractions followed the order of oxide bound
> organically bound > specifically adsorbed > readily soluble boron. Total boron was
highest in Northern dry zone (582.3 mg kg-1). Residual boron has minimum effect on
available boron, whereas fractions like readily soluble boron, specifically adsorbed
boron, oxide bound boron and organically bound boron contribute towards plant
available. Readily soluble and specifically adsorbed boron had positive correlation with
pH and available boron, residual and total boron had a positive correlation with organic
carbon. Adsorption behaviour of boron followed both Freundlich and Langmuir
isotherms. Amount of boron adsorbed was more in Northern dry zone and least in
Southern dry zone. The adsorption and fractionation scheme proved to be satisfactory in
terms of sensitivity and positioning of soil boron. The methodology should be useful in
determining the effects of soil management practices on soil boron status and in
monitoring changes in boron distribution with time due to the various soil practices.