STUDIES OF SOIL ORGANO-MINERAL FRACTIONS

Sand-, silt-, and clay-size organo-mineral fractions were isolated in bulk from surface horizons of five soils following ultrasonic dispersion in water. Good clay separation was achieved for all except one highly organic, calcareous clay soil. Organic-N and -C were concentrated in the clay and silt fractions but for each soil the organic C : N ratio decreased in the order sand > silt > whole soil > clay. Acid hydrolysis of the silt and clay fractions revealed a slight concentration of amino acid-N and NH₄-N in the clays but only small differences in the distribution of individual amino acids were observed. The results suggest that both silt and clay fractions may be important in the stabilization of soil organic matter.