STUDIES OF SOIL ORGANIC-MATTER DYNAMICS USING NATURAL CARBON ISOTOPES

In continuation of previous investigations, the depth distributions of the natural abundances of C-13 and C-14 isotopes were studied in two paddy soil profiles of the Philippines and Taiwan. The depth distributions show the regularity and depth of puddling. Further, the soils can be clearly distinguished with regard to their rate of decomposition and metabolism of organic matter and of the vertical translocation of metabolites. In addition, long-term fixation of organic matter by clay could be detected within a clay-enrichment zone in the subsoil. At the horizon boundaries in one soil, continual rejuvenation of soil organic matter was found, due to pore discontinuities impeding the percolation of organic substances.