Canola root rot and yield response to liming and tillage

No-till is replacing conventional tillage in many areas, but information regarding tillage effects on crop, soil, and weed response to liming of acid soils is needed for canola (Brassica campestris L.) production. A Hythe clay loam (fine, montmorillonitic, frigid Mollic Cryoboralf) with initial pH in CaCl2 approximate to 5 was limed (7.5 Mg ha(-1)) in May 1991. Liming increased soil pH to 6.6 in the fall 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 NO3-N in the 0- to 20-cm depth significantly, but no change was detected in exchangeable Al, NH4-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 Kuhn) and increased grain yield of canola. 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 grain yield by liming was 0.39 (37%) Mg ha(-1) yr(-1) in tilled and 0.22 (17%) Mg ha(-1) yr(-1) in no-till soil. Liming increased dry matter by 1.77 Mg ha(-1) yr(-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 NO3-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.