Properties and distribution of humic substances and inorganic structure-stabilizing components in particle-size fractions of cultivated mediterranean soils

Aggregate-size fractions of two cultivated calcareous Mediterranean soils (Mevo Horon and Palmahim) were characterized with regard to organic matter and other soil components involved in soil structure stabilizing reactions. The parameters determined in each aggregate-size fraction included: particle size distribution and contents of CaCO 3 , organic C and N, fulvic acid fraction (FF), humic acid (HA), total humic substances (HS), and extractable Al and Fe. Except for the organic C and HS in the Mevo Horon (MH) soil, all of the calculated ratios between the contents of each of the components in any size fraction and that calculated for the same component in the 250 μm) and the smallest (<2 μm) aggregate-size fractions. Higher polysaccharide content was observed in the larger particle size fraction, reflecting the influence of recent plant material.