THE OCCURRENCE OF INTERLAYER CLAY-ORGANIC COMPLEXES IN TWO NEW ZEALAND SOILS

By using x-ray diffractometry and 13C-NMR spectroscopy, in combination with chemical and heat pretreatments, we have found good evidence for the occurrence of interlayer clay-organic complexes in two New Zealand soils. Here, the clay mineral is a regularly interstratified mica-smectite, and the organic species is a humic substance with a polymethylene chain structure. The organic material in the complex is resistant to peroxidation and pyrophosphate extraction. It is also thermally stable, being extensively decomposed only after the complex is heated at 400°C. A combination of soil factors seems necessary for interlayer complex formation. This includes a smectitic clay mineralogy, an accumulation of organic matter associated with a low microbial activity, and a highly acid soil reaction.