Soil-organic-matter stability in sandy cropland soils is related to land-use history

Sandy cropland soils in NW Europe were found to contain unusually high organic-carbon (OC) levels, and a link with their land-use history has been suggested. This study's aim was to assess the discriminating power of physical and chemical fractionation procedures to yield information on soil-organic-matter (OM) stability for these soils. In relict- and cultivated-heathland soils, much higher proportions of 6% NaOCl treatment-resistant but 10% HF-soluble OC (MOC) and N (32.2% and 29.9%) were measured compared to a set of permanent-cropland soils without a history of heathland land use (11.9% and 8.5%). Also, the proportions of 6% NaOCl- and 10% HF treatment-resistant OC and N in the relict and cultivated heathlands (19.2% and 12.0%) were higher than in the permanent-cropland soils (17.7% and 5.7%). Stepwise multiple linear-regression yielded a significant relationship between the annual mineralization (g C [100 g OC](-1)), soil OC (g C kg(-1)) content, and %MOC: Annual mineralization = 4.347 - 0.087 soil OC - 0.032 %MOC (R(2) = 0.65). Combinations of incubation experiments for quantification of the labile soil OM pool with chemical fractionation may thus yield meaningful data for development of soil-organic-matter models with measurable pools, but their applicability will be limited to specific combinations of former land use with soil, climate, and current management.