Turnover of organic matter in soils as traced by radiocarbon

Radiocarbon has been used as a tracer during a period of 30 years to study the transformations of organic matter in soils. This paper reviews decomposition studies with 14C-labelled plant residues and manure materials under laboratory and field conditions. In spite of some inherent experimental limitations, considerable new knowledge has been obtained about the processes and rates of decomposition, humification and carbon retention, respectively. Some of the traditional assumptions concerning the transformations of manure carbon in soils have to be reconsidered in the light of these findings. (author)