A ROUTINE METHOD TO STUDY SOIL ORGANIC-MATTER BY PARTICLE-SIZE FRACTIONATION - EXAMPLES FOR TROPICAL SOILS

Particle size fractionation is becoming commonly used for studying soil organic matter (OM). However, isolation of clay and silt represents a long and thus tedious step in the fractionation procedure. We propose an approach identical to the one utilized in particle size analysis with an estimation of the recoveries from aliquots (''aliquot'' method) of the 0-2 and 0-20 mu m fractions and no entire isolation (''decanting'' method) of clay and silt. In comparison with the ''decanting'' method, the fraction and carbon (C) recoveries obtained ay the ''aliquot'' method were satisfactory, but those of nitrogen (N) being hardly interpretable because of an insufficient accuracy of the determination method. The recommended method saves time and laboratory space and could. be used as a routine particle size fractionation of soil OM. Finally, this paper lists various methodological aspects of considerable significance but rarely reported in published studies.