Labile and stable organic matter components in agricultural soils

The article presents an analysis of the literature on labile and stable components of organic matter (OM) in agricultural soils. The labile components include light fractions (LF) identified by particle density (< 1.8 g·cm -3 ), while the stable components include clay fractions (Clay) identified by particle size (<1–2 μm). Labile components of OM are very sensitive, while stable components are insensitive to changes in farming and land use systems. As a result, the ratio of carbon in the labile and stable pools, the C LF /C Clay ratio, is used as an indicator of the OM quality in agricultural landscapes. Physical soil fractionation methods used to isolate labile and stable components of OM are laborious and, therefore, not suitable for regional and global scale studies. The proposed theoretically substantiated express indicators of OM can be obtained using the proposed fairly simple granulometric fractionation method. These express indicators of OM will be characterized by different biogeochemical stability and their application for long-term and operational carbon monitoring in soils seems very promising. Experimental verification of theoretically justified simplified indicators is recommended in order to identify among them the correct indicators that most adequately reflect the impact of native and anthropogenic factors on the soil OM quality at different time scales.