The Nature of Sequestered Carbon in Different Irish Mineral Soils

Humic substances (HS) provide the major sinks for carbon (C) in soils. Although HS have a degree of resistance to microbial degradation, they are degraded in time. Humin, the HS component in association with the soil mineral colloids, has greatest resistance to degradation. To understand the extent to which soil can be a sink for C it is important to know the soil mineralogy, and to be aware of aspects of the structures of the humic components. Enhanced biological oxidation occurs in soils in long term cultivation. Its effects can be observed by comparing the amounts and compositions of the humic components in cultivated soils with those in the same soil types in long term grassland. Three such paired soils were included in the study as well as three grassland soils that are in new lysimeter studies at the Environmental Research Centre, Johnstown Castle. In a study of the humification process, maize (Zea mays L., a C4 plant, with a 13C value of the order of 12) was incubated in calcareous organic C-free sand, and the products were studied in the same way as those from the soils