Weed population dynamics in diversified cropping systems of the Northern Great Plains
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Date
2004
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Montana State University - Bozeman, College of Agriculture
Abstract
Small grain/fallow-based cropping systems of Montana and the Northern Great Plains are largely
viewed as unsustainable from both an economic and environmental perspective. As a result, interest in
alternative cropping systems has increased. A component of these alternative systems is increased crop
diversity, but a major obstacle to adopting more diverse crop rotations is concern about weed
management during the transition to the new system. I investigated changes in weed population
dynamics during this transition period to some alternative systems in MT.
Temporal dynamics of wild oat and redroot pigweed populations as affected by crop rotations and
management intensity (conventional vs. reduced input levels) were examined. I found that crop
diversity and accompanying crop management practices can be effective weed management tools
during the transition to reduced input cropping systems. Crop rotation alone, however, in both the
conventional or reduced input systems had little impact on weed populations when it was decoupled
from corresponding chemical weed management practices.
In addition, I examined the temporal and spatial dynamics of wild oat, Persian darnel, and redroot
pigweed as part of the same field study. I quantified metrics that described weed population growth or
decline in different crop rotations across conventional, reduced, and organic input cropping systems. A
methodology for graphically depicting the combined temporal and spatial dynamics of a weed
population was developed. This data set was then used to investigate the importance of variables
hypothesized to be important drivers of observed wild oat population dynamics. Using multiple linear
regression techniques, the best predictors of wild oat seedling abundance were determined to be wild
oat seedling density and proximity to wild oat seedling density the previous growing season. The
overall predictive power of our models however was low, but may indicate that wild oat populations
persist in cropping systems by continuously forming new colonies in response to management more
than any other single factor.
Results of these studies highlight the gaps in our knowledge base related to identifying the mix of
fundamental ecological processes and management that drive observed weed population dynamics.
These results also demonstrate the data requirements needed to develop an understanding of weed
population dynamics in agroecosystems.