RESUMO
Grazing of natural rangeland and seeded pasture is an important feeding strategy for the Canadian beef cattle industry. As a consequence, beef cattle population has a direct influence on the proportion of land base maintained as perennial forage, which in turn changes soil organic carbon (SOC) stocks. We examined historical relationships between the net change in SOC resulting from perennial/annual crop conversion and beef cattle populations. We observed strong negative linear relationships, both regionally and nationally, between the population of beef cattle and the estimated change in SOC (negative sign indicating soil C sink) resulting from the conversion of annual crops and vice versa. These relationships indicate that as beef cattle population declines there is a corresponding loss of SOC resulting from a reduction in the relative proportion of perennial to annual crops on the landscape. The annual C loss resulting from land use conversion was roughly equivalent to 62% (±13%) of the combined enteric and manure annual emissions of CH4 and N2O [(1400 (±440) kg CO2 eq head-1 yr-1] resulting in net greenhouse gas emissions of 850 (±360) kg CO2 eq head-1 yr-1. These results highlight the importance of an integrated analysis that considers land use conversion and its impact on SOC when assessing the environmental footprint associated with beef cattle production.
