Soil carbon changes in cultivated land converted to grasses in south-central Saskatchewan
Soils play an important role in the carbon cycle. Under natural conditions, soil organic carbon forms an equilibrium with the environment. Disruption to this equilibrium can transform the soils into either a source or a sink for atmospheric CO2. Mensah (2000) found in the Black and Gray soil zone that the conversion of marginal cultivated land to grassland resulted in an increase in soil organic carbon of 0.6 Mg C ha-1 yr-1 to 1.2 Mg ha-1 yr-1 (0-15 cm depth) across the landscape over a ten year period. However, little information is available on carbon sequestration rates from grassland restoration in the Brown and Dark Brown soil zones of the southern Prairies. The Missouri Coteau region in southern Saskatchewan is comprised predominantly of Brown and Dark Brown soils that, due to steep topography and stoniness, pose limitations for production of annual crops. The effect of conversion to grassland on the forms and distribution of soil carbon was examined using side-by-side paired cultivated and grassland catenae that had been in a grass seed-down for about eight years. Total soil organic carbon in the 0-15 cm depth of the shoulder, midslope and footslope positions were measured. The shoulder positions showed the greatest increase in soil organic carbon from grass seed-down, with an average apparent increase in soil carbon of 1.62 Mg ha-1 yr-1. Carbon distribution with depth was found to be dependent upon the cropping history of the cultivated equivalent as well as the parent material. Greatest apparent carbon gains were observed when the cultivated comparable was in a cereal-fallow rotation and the lowest gain from grass seed-down occurred when the cultivated comparable contained a legume in rotation.
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