Organic carbon, organic matter and bulk density relationships in boreal forest soils

Relationships between soil organic carbon (SOC), organic matter (SOM), and bulk density (BD) were established in acidic loamy to sandy loam fine fractions of forest soils in Quebec (Canada). The interest of such relationships rests with the possibility of using simple and rapid techniques to estimate SOC and BD. It is also a crucial step in establishing the correspondence among several databases when SOC data are obtained using different measurement techniques. In this study, SOC was measuredby dry combustion (SOCN DC ) and wet digestion (SOC WD ) methods, and organic matter by loss-on-ignition (LOI). Our results suggest that, in these soils: (1) LOI can be used for estimating SOC (r 2 = 0.95, RMSEP = 16%) and SOC DC /SOM significantly decreased with increasing depth from 0.49 to 0.27; (2) SOC DC and SOC WD were highly correlated. Even if SOC WD provided near complete recovery of SOC DC , dry combustion remains the preferred method for SOC analysis since recovery decreased with increasing depth from 100 to 83%. (3) BD was also strongly related to SOM(r 2 = 0.81). We recommend using the organic density approach to estimate BD from SOM because it allows BD to be predicted without significant bias and with a degree of accuracy of 14%. Key words: Forest soils, soil organic carbon, soil organic matter, soil bulk density