Soil carbon dynamics in Canadian Agricultural Ecoregions:: Quantifying climatic influence on soil biological activity

Climate is the major determinant of soil biological activity, including the decomposition rates of soil organic carbon (SOC) components. The objective of this study was to estimate the influence of climate on SOC dynamics, using long-term standard weather station data for Canadian Agricultural Ecoregions and the Introductory Carbon Balance Model for regional applications (ICBMregion). Mean daily temperature, total precipitation and potential evapotranspiration data were used in pedotransfer, soil water balance and biological activity functions to calculate a climate factor, r(e-clim), used to describe both inter- (1970-1999 data, daily r(e-clim)) and intra-annual variation (1903-2000 data, mean annual r(e-clim)) of the effects of climate on SOC decomposition rates across the country. When r(e-clim) = 1.0 the SOC decomposition rate is equal to that at a reference site in Central Sweden: when it is < 1.0 the relative SOC decomposition rate is lower, and when it is > 1.0 it is higher. The results show that the cool and humid eastern Canadian Agricultural Ecoregions are characterized by higher SOC decomposition rates (average r(e-clim) = 1.20), compared to the semi-arid regions of western Canada (average r(e-clim) = 0.95). In other words, more C input is needed to maintain a certain SOC level in eastern than in western Canada. Inter-annual variation (the difference between minimum and maximum values) in r(e-clim) for a given agricultural ecoregion was approximate to +/- 20%. The patterns of variation in intra-annual r(e-clim) values differed between Agricultural Ecoregions: for eastern Canada r(e-clim) reached a peak of approximate to 3.5 in mid-summer, and that of western Canada peaked at approximate to 2.5. This concept of r(e-clim) was tested and used in other climate zones such as northern Europe and Sub-Saharan Africa, and enabled us to integrate large data sets concerning climate and SOC dynamics and to characterize Canadian Agricultural Ecoregions by one variable, r(e-clim). (c) 2007 Elsevier B.V All rights reserved.