ANIL KUMAR, K. SANITHA, M. S2016-12-222016-12-2240865Th-9915http://krishikosh.egranth.ac.in/handle/1/92223A 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.enThesis