The net flux of carbon from agricultural soils in Canada 1970-2010

Changes in soil organic carbon (SOC) in agricultural soils influence soil q uality and greenhouse gas concentrations in the atmosphere. Land use, manag ement practices, soil characteristics, and climate influence such changes. Using the Century model we estimated the rate of SOC change in agricultural soils of Canada for the period 1970 to 2010. This estimation was based on the estimated SOC change for 15% of the 1250 agriculturally designated soil landscape of Canada (SLC) polygons. Simulations were carried out for two t o five crop rotations and for conventional and no-tillage. The results indi cate that the agricultural soils in Canada, whose SOC are currently very cl ose to equilibrium, will stop being a net source of CO2 and will become a s ink by the year 2000. Rates of carbon change for the years 1970, 1990, and 2010 were estimated to be -67, -39, and 11 kgC ha(-1) The rate of decline i n the carbon content of agricultural soils in Canada has slowed considerabl y in the 1990s as a result of an increase in the adoption of no-tillage man agement, a reduction in the use of summer fallowing, and an increase in fer tilizer application. We estimate that the proportion of agricultural land s toring SOC will have increased from 17% in 1990 to 53% by the year 2000.