Soil & Tillage Research 42 (1997) 229-240 Changes in total, mineralizable and light fraction soil organic matter with cropping and tillage intensities in semiarid southern Alberta, Canada ’ Francis J. Larney *, Eric Bremer 2, H. Henry Janzen, Adrian M. Johnston 3, C. Wayne Lindwall 4 Research Centre, Agriculture and Agri-Food Canada, PO Box 3000. Lethbridge, Alta., TlJ 4Bl. Cunuda Accepted 2 1 January 1997 Abstract There has been a trend toward increased cropping intensity and decreased tillage intensity in the semiarid region of the Canadian prairies. The impact of these changes on sequestration of atmospheric CO, in soil organic carbon (Cl is uncertain. Our objective was to quantify the changes in total, mineralizable and light fraction organic C and nitrogen (N) due to the adoption of continuous cropping and conservation tillage practices. We sampled three individual long-term experiments at Lethbridge, Alberta, in September 1992: a spring wheat (Triticum aestivum L.)-fallow tillage study, a continuous spring wheat tillage study and a winter wheat rotation-til- lage study. Treatments had been in place for 3-16 years. In the spring wheat-fallow study, different intensities (one-way disc > heavy-duty cultivator > blade cultivator) of conventional tillage (CT) were compared with minimum tillage (MT) and zero tillage (ZT). After 16 years, total organic C was 2.2 Mg ha-’ lower in more intensively worked CT treatments (one-way disc, heavy-duty cultivator) than in the least-intensive CT treatment (blade cultivator). The CT with the blade cultivator and ZT treatments had similar levels of organic C. The CT treatments with the one-way disc and heavy-duty cultivator had light fraction C and N and mineralizable N amounts that were about 13-18% lower than the CT with the blade cultivator, MT or ZT treatments. In the * Corresponding author. Tel: (403) 317-2216; Fax: (403) 382-3156; e-mail: larney@em.agr.ca; ’ Lethhridge Research Centre Contribution No. 3879434. 2 Current address: Agrium Inc., PO Box 3000, Lethbridge, Alberta TlJ 4B1, Canada ’ Current address: Research Farm, Agriculture and Agri-Food Canada, PO Box 1240, Melfort, Saskatchewan SOE lA0, Canada 4 Current address: Semiarid Prairie Agricultural Research Centre, Agriculture and Agri-Food Canada, PO Box 1030, Swift Current, Saskatchewan S9H 3X2, Canada 0167-1987/97/$17.00 0 1997 Elsevier Science B.V. All rights reserved. PZZ SO167-1987(97)00011-l