BARLEY, CANOLA, AND WEED GROWTH WITH DECREASING TILLAGE IN A COLD, SEMIARID CLIMATE

Conventional tillage systems are reported to cause soil degradation, Set appropriate conservation tillage practices have not been developed for cold regions of the northern Canadian Prairies. Effects of conventional, reduced, and zero tillage systems (CT, RT, and ZT) on the growth of dryland spring barley (Hordeum vulgare L.), canola (Brassica campestris L.), and weeds were studied on a clay soil (Natriboralf) near Rycroft in northern Alberta. Each crop-tillage combination was fixed in space from 1989 through 1991. Each season, the CT plots were tilled once in the preceding fall. and twice in the spring prior to seeding; the RT plots were tilled once prior to seeding in the spring; the ZT plots received a preseeding glyphosate [N-(phosphonomethyl)glycine] application in the spring. Crop residue in ZT was spread evenly by harrowing in the spring just prior to seeding. The 1998 available NO3-N, NH4-N, and P in soil or total plant N and P were unaffected by tillage, except that NO3-N was lower under ZT canola. No consistent effect of tillage was detected on total soil moisture, except for lower moisture in the 0- to 10-cm depth under CT in dry periods. As the study progressed, there was a trend of increased weed population response to tillage, relatively greater weed density under ZT, and a shift in species composition. Mean barley total dry matter (TDM) yield was 3.37, 3.09, and 2.93 Mg ha(-1) and grain yield was 1.59, 1.41, and 1.35 Mg ha(-1) under RT, ZT, and CT, respectively. Mean canola TDM yield was 2.92, 2.36, and 2.12 Mg ha(-1) and grain yield was 0.84, 0.66, and 0.59 Mg ha(-1), under RT, CT, and ZT, respectively. In most cases, however, tillage effects on mean crop yields were nonsignificant (P less than or equal to 0.05). Overall, RT was considered to be agronomically and environmentally desirable, due to somewhat better crop yield than either CT or ZT systems and two fewer cultivations than CT.