MOLECULAR SIZE DISTRIBUTION OF HUMIC ACIDS EXTRACTED FROM WATER STABLE AGGREGATES OF DIFFERENT SIZES

Abstract

Humic  Acids  (HA)  extracted  by  0.1  M  NaOH-pyrophosphate  mixture from  water  stable  aggregates  of  different  sizes  (0.25,  0.5,  1.0,  2.0 mm)  were  fractionated  using  Sephadex  gels  into molecules of  different  size  ranges.  It  was observed  that  smaller  sized  aggregates  contained  greater  proportion  of  high  molecular weight  of  humic acid  molecules  (>  10,000)  in  contradistinction  to  larger aggregates which contained more  of  small  molecules  (<  700).  The  size  range  of  HA  molecules  as a  factor  in  determining  aggregate  size  in  soil  is  discussed.