Abstract
To reduce reliance on herbicides and maintain crop productivity, integrated weed management (IWM) seeks to optimize synergies between diverse sets of weed management practices combined at the cropping system scale. Nevertheless, data on weed community response to the long-term implementation of IWM practices remain scare. Here, we assessed the effects of four IWM systems with contrasting objectives and practices (S2: transition from superficial tillage to conservation agriculture; S3: no-mechanical weeding; S4: mixed mechanical and chemical weeding; S5: herbicide-free; all with 6 year rotations) compared to a conventional reference (S1: herbicide-based with systematic plowing and a 3 year rotation) on taxonomic and functional weed community composition and structure after 17 years of continuous implementation. We examined the legacy effects of these systems with a uniformity trial consisting of winter wheat managed uniformly across the systems as well as with a novel in situ weed seedbank approach involving tilled strips. We found that resulting weed communities in IWM systems were more species rich (species richness from 1.1 to 2.6 times greater) and more abundant (total density from 3.3 to 25 times greater) than those observed in the reference system, and differed in term of taxonomic and functional composition. In addition, we found that, when systems shared the same weed species, germination patterns of two thirds of the species differed between systems, highlighting the selection pressures some IWM practices exert on weeds. We showed that analyzing the superficial germinable seedbank in situ with tilled strips could provide a comprehensive view of resulting weed communities and be helpful in developing cropping systems that foster agroecological weed management.
Highlights
Effective weed management is recognized as crucial for the ecological intensification of agriculture (Petit et al, 2015) because weeds can generate severe yield losses (Oerke, 2006) and current approaches to weed management rely heavily on herbicides
We found that 17 years of continuous implementation of integrated weed management (IWM) resulted in germinable seedbank and emerged weed communities that were more species rich and more abundant than those observed in the reference system, validating our first hypothesis
We assessed the legacy effects of IWM cropping systems implemented over years on the superficial germinable weed seedbank and emerged weed flora in a uniformly managed winter wheat trial conducted in year
Summary
Effective weed management is recognized as crucial for the ecological intensification of agriculture (Petit et al, 2015) because weeds can generate severe yield losses (Oerke, 2006) and current approaches to weed management rely heavily on herbicides. To reduce herbicide reliance and maintain crop productivity, integrated weed management (IWM) strategies aim to both disrupt. Legacy of Long-Term IWM Systems weed population dynamics and reduce weed interference by coherently combining a diversity of chemical, physical, and cultural weed management practices at the cropping system scale (Harker, 2013). These practices are combined in ways that optimize synergistic interactions among practices by targeting weeds in complementary ways and at different stages in their life cycles (Ryan et al, 2011). Effective IWM strategies keep weed populations below economic thresholds while maintaining or enhancing weed diversity (Liebman and Gallandt, 1997). The degree to which contrasting IWM strategies can shift the ecology and/or biology of arable weeds over the long-term is largely unexplored but of critical importance to move toward more sustainable alternatives to herbicides (Neve et al, 2018)
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