In a field trial near Beaverlodge, Alberta, a Hythe clay loam (fine, montmorillonitic, frigid Mollic Cryoboralf) with initial pH in CaCl 2 ~5 was limed (7.5 t ha -1) in May 1991. Liming increased soil pH to 6.6 in the autumn of 1991. During 1993 to 1995, the pH of limed soil at the 0- to 10-cm depth ranged from 6.2 to 6.3 when conventionally tilled and from 5.6 to 6.2 under no-till. A slight increase at the 10- to 20-cm depth and no change below 20 cm occurred in soil pH due to liming. Liming increased NO 3-N in the 0- to 20-cm depth significantly, but no change was detected in exchangeable Al, NH 4-N and extractable P. Weed populations were not affected by liming in 1993 and 1994, but were suppressed markedly in 1995. Liming reduced brown girdling root rot (BGRR) (caused by Rhizoctonia solani) and increased seed yield of canola [rape]. Three-year mean BGRR ratings (a scale of 0 to 5 scale, from disease-free to disease-impaired) under no lime and lime, respectively, were 2.96 and 2.59 in tilled and 2.76 and 2.63 in no-till soil. The increase in canola seed yield by liming was 0.39 (37%) t ha -1 year -1 in tilled and 0.22 (17%) t ha -1 year -1 in no-till soil. Liming increased dry matter by 1.77 t ha -1 year -1 (31%). No-till plots had higher soil water and canola yields but slightly lower soil pH (0- to 20-cm depth), and lesser BGRR, compared with the tilled system. Increased soil NO 3-N and pH, fewer weeds, and reduced BGRR-all responded to liming and contributed to increased canola yields under both tilled and no-till systems.
