MANAGEMENT EFFECTS ON SOIL C STORAGE ON THE CANADIAN PRAIRIES

The Canadian prairie, which accounts for about 80% of Canada's farmlan d, has large reserves of soil organic carbon (SOC), Changes in the siz e of the SOC pool have implications for soil productivity and for atmo spheric concentrations of CO2, an important 'greenhouse gas'. We revie wed recent findings from long-term research sites to determine the imp act of cropping practices on SOC reserves in the region. From this ove rview, we suggest that: (1) the loss of SOC upon conversion of soils t o arable agriculture has abated; (2) significant gains in SOC (typical ly about 3 Mg C ha(-1) or less within a decade) can be achieved in som e soils by adoption of improved practices, like intensification of cro pping systems, reduction in tillage intensity, improved crop nutrition , organic amendments, and reversion to perennial vegetation; (3) chang es in SOC occur predominantly in 'young' or labile fractions; (4) the change in SOC, either gain or loss, is of finite duration and magnitud e; (5) estimates of SOC change from individual studies are subject to limitations and are best viewed as part of a multi-site network; and ( 6) the energy inputs into agroecosystems need to be included in the ca lculation of the net C balance. The long-term sites indicate that Cana dian prairie soils can be a net sink for CO2, though perhaps only in t he short term. These sites need to be maintained to measure the effect s of continued agronomic evolution and predicted global changes. (C) 1 998 Agriculture and Agri-food Canada. Published by Elsevier Science B, V.