Does diversifying crop rotations suppress weeds? A meta-analysis

Abstract

Over the past half-century, crop rotations have become increasingly simplified, with whole regions producing only one or two crops in succession. Simplification is problematic from a weed management perspective, because it results in weeds’ repeated exposure to the same set of ecological and agronomic conditions. This can exacerbate weed infestations and promote the evolution of herbicide resistance. Diversifying crop rotations through addition of crop species and their associated managements may suppress weeds and reduce selection pressure for herbicide resistance by altering stress and mortality factors affecting weed dynamics. Here we report the results of a meta-analysis using 298 paired observations from 54 studies across six continents to compare weed responses due to simple and more diverse crop rotations. We found diversifying from simple rotations reduced weed density (49%), but did not have a significant effect on weed biomass. We investigated the effect of management practices, environmental factors, and rotation design on this effect. Diversification that increased the variance around crop planting dates was more effective in suppressing weeds than increasing crop species richness alone. Increasing rotational diversity reduced weed density more under zero-tillage conditions (65%) than tilled conditions (41%), and did so regardless of environmental context and auxiliary herbicide use. Our findings highlight the value of diversifying crop rotations to control weed populations, and support its efficacy under varied environmental conditions and management scenarios.

Cropping System Redesign for Improved Weed Management: A Modeling Approach Illustrated with Giant Ragweed (Ambrosia trifida)

“…Thus, PIVI was more useful than species number in predicting the weed suppression ability of given crop rotation. These modeling outcomes accord with the theoretical insight provided by Gaba et al [15] and corroborate the results of the meta-analysis of empirical data reported by Weisberger et al [14]. the 2-year rotation had a PIVI value of 11.8, the 6-year rotation had a PIVI value of 98.0, with intermediate PIVI values for the other rotations.…”

“…To characterize differences among rotation systems in temporal patterns of management activities, we calculated a planting interval variation index (PIVI). The PIVI was defined as the coefficient of variation of the number of months between plantings of succeeding crops in each complete rotation cycle [14]. We examined the relationship between the PIVI value for each rotation system and the level of control efficacy needed in corn and soybean to prevent increases in giant ragweed seed densities.…”

“…This diversification should reduce selection of weed populations for resistance, limit shifts in weed community composition toward especially problematic species, and minimize the risks of weed control failures due to mitigating factors such as weather conditions [13]. In a recent meta-analysis of data from field experiments, Weisberger et al [14] found that diversifying crop rotation sequences with additional species reduced weed densities by an average of 49%, regardless of auxiliary herbicide use. Furthermore, the diversification effect on weed density was greatest for rotation sequences with the largest variance around crop planting dates.…”

Expression of N‐cycling genes of root microbiomes provides insights for sustaining oilseed crop production

“…Over the past half‐century, the level of crop diversity in cropping systems has declined in favour of intensive monocultures or systems with only two crops in rotation (Weisberger et al ., 2019). However, these simplified cropping systems have their pitfalls and are not sustainable (Martens et al ., 2015).…”

Winter annual alternative crops for enhanced sustainability in Iowa cropping systems

“…Increases in cropping system diversity also effectively managed weed species and populations (Weisberger et al, 2019), reduced disease incidence and severity (Leandro et al, 2018), increased yield and yield stability (Smith et al, 2008;Gaudin et al, 2015), and sustained soil quality and productivity (McDaniel et al, 2014). Extending crop rotations allows producers to effectively manage some pests by altering the spatial and temporal diversity in their fields (Davis et al, 2012).…”