Abstract
Rapid growth of cool-season weeds in the spring exacerbates weed interference during early soybean (Glycine max (L.) Merr.) establishment in northern climates. This study tested the utility of spring-seeded inter-row living mulches in soybean for early season weed suppression using volunteer canola (Brassica napus L.) as a representative model weed species. The effects of the presence or absence of spring wheat (Triticum aestivum L.) or winter cereal rye (Secale cereale L.) living mulches (mulch type) that had been seeded simultaneously with soybean grown using 38 or 76 cm row spacing (spatial arrangement) and the presence or absence of herbicides used for mid-season mulch termination (herbicide regime) were evaluated in three environments in Manitoba, Canada, in 2013 and 2014. Soybean yield was similar in the presence and absence of the living mulches. In the environment that received the lowest precipitation (Carman 2013), the mulches terminated with post-emergence glyphosate resulted in a 55% greater soybean yield compared to the mulches that remained live throughout the growing season. Inter-row mulches that had been living or terminated mid-season reduced volunteer canola seed production by about one-third (up to 9000 seeds m−2). This study demonstrates the utility of wheat or cereal rye inter-row living mulches for enhanced interference with weeds during early soybean establishment.
Highlights
Soybean biomass was roughly 30% reduction in soybean yield compared to the mulches that were terminated mid-season (Table 1)
Spring-seeded wheat and cereal rye inter-row living mulches were a viable option to facilitate the early season suppression of volunteer canola in soybean grown in the Northern Great Plains region of North America
Close monitoring of precipitation is warranted to mitigate potential mulch-induced soybean yield losses, while early season precipitation could be used as a trigger for the termination of living mulches mid-season, if required
Summary
Canola can become a problematic volunteer weed since seed lost during crop harvest [4] can enter secondary dormancy, resulting in a moderately persistent seedbank that persists throughout short crop rotations [5]. Proactive management, including the minimization of harvest losses [4,6] and increased seedbank decline with timely soil disturbance [7], can reduce volunteer canola population densities. Uncontrolled volunteers in subsequent crops can return seed to the soil seedbank [8], resulting in population persistence and the emergence of this weed several years after canola production [9]. Limiting volunteer canola seed production and return to the soil seedbank is imperative to mitigating the establishment of this weed in soybean production systems
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