Abstract
Experiments were established on irrigated land at Lethbridge, Alberta, to determine the effect of timing and method of alfalfa (Medicago sativa L.) termination on weed abundance, soil moisture and N content, cereal yield and colonization of roots by vesicular arbuscular mycorrhizal (VAM) fungi. Alfalfa growth was terminated using no, minimum, and conventional tillage in either late summer, early fall, or spring. Herbicide was applied or tillage was used to control volunteer alfalfa, dandelion (Taraxacum officinale Weber), stinkweed (Thlaspi arvense L.), and kochia [Kochia scoparia (L.) Schrader] before seeding cereals. Dandelion and volunteer alfalfa density tended to be greatest after no-tillage treatments, and poor in-crop alfalfa control likely reduced cereal yields in no-tillage plots. In contrast, the major in-crop broadleaf weed, redroot pigweed (Amaranthus retroflexus L.), was most dense (7 plants m-2) in tilled plots. Both wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.) yields were reduced 9 to 12% after alfalfa termination with no-tillage treatments compared with minimum or conventional tillage. In spring, after seeding, available soil N content averaged 138, 101 and 79 kg ha-1 for conventional-, minimum-and no-tillage plots, respectively; however, fall no-tillage treatments seemed to supply sufficient N for wheat and barley. Soil moisture content tended to be similar after all termination treatments. Wheat and barley responded differently to time and method of termination in terms of seedling root length and colonization by VAM fungi. The percentage of root colonized by VAM fungi was greater on both barley and wheat in no-tillage compared to cultivated treatments. It may be possible to have similar wheat and barley yields after no tillage and tilled alfalfa termination if no-tillage termination is initiated in fall and effective incrop herbicides are used for volunteer alfalfa and dandelion control. Key words: Alfalfa termination, no-tillage, N, vesicular arbuscular mycorrhizal fungi, weed density
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