Cereal rye mulch biomass and crop density affect weed suppression and community assembly in no-till planted soybean

Authors: MENALLED, URIEL - Cornell University; ADIEUX, GUILLAUME - University Of Franche-Comte; CORDEAU, STEPHANE - University Of Franche-Comte; SMITH, RICHARD - University Of New Hampshire; Mirsky, Steven; RYAN, MATTHEW - Cornell University

Submitted to: Ecosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/14/2022
Publication Date: 6/19/2022
Citation: Menalled, U.D., Adieux, G., Cordeau, S., Smith, R.G., Mirsky, S.B., Ryan, M.R. 2022. Cereal rye mulch biomass and crop density affect weed suppression and community assembly in no-till planted soybean. Ecosphere. 13:6.Article number e4147. https://doi.org/10.1002/ecs2.4147.
DOI: https://doi.org/10.1002/ecs2.4147

Interpretive Summary: No-till organic farming involves growing crops without herbicides (since there are no cost-effective organic-certified herbicides on the market) and tillage (which damages the soil). However, herbicides and tillage are historically the two most common ways of controlling weeds; avoiding both makes weed management difficult. Instead, organic no-till farming calls for cultural weed management strategies such as the use of cover crops and high-density cash crop planting to suppress and out compete weeds. We conducted a study to evaluate how soybean planting density and varied levels of cover crop mulch affect the types of weeds and their traits. High levels of cover crop mulch suppressed annual weeds, meaning perennial weeds became more predominant. However, increased soybean planting density decreased perennial weed biomass. This research demonstrated the synergy between cultural weed control methods (i.e. the combined use of cover crops and increased soybean planting density) and will be of interest to farmers and scientists interested in organic no-till cropping with guidance on weed control methods.

Technical Abstract: 1. Organic no-till farming requires less labor and fuel than traditional tillage-based organic crop production; however, without soil tillage or synthetic herbicides, weed suppression is highly dependent on effective cultural weed management. To develop robust ecological weed management strategies, it is important to consider the effects of cultural management practices on weed communities. 2. An experiment was conducted to assess how soybean Glycine max (L.) Merr. density and cereal rye Secale cereale L. mulch biomass affected weed suppression and community assembly in an organic no-till system. Soybean was seeded at five rates from 0 to 74 seeds m-2 and five cereal rye mulch levels were established from 0 to 2 times the ambient cereal rye biomass within each site-year. We assessed the effects of soybean density and cereal rye mulch biomass on weed suppression, weed community composition, and the functional diversity of weed life cycle, emergence timing, seed weight, height, and specific leaf area traits. 3. Weed suppression was influenced by a synergistic interaction between high soybean density and cereal rye biomass. The functional dispersion of all weed traits, when combined, was reduced by increased soybean density and mulch biomass, suggesting that high treatment intensities induced trait convergence. However, soybean density and cereal rye biomass had differing effects on the functional dispersion and composition of individual traits, suggesting that these management practices represent unique filters during weed community assembly. 4. Synthesis and application: Increased soybean density and cereal rye mulch biomass affected weed community assembly by constraining trait dispersion and shifting functional composition. Mulch biomass had a larger effect on annual weed suppression and weed community composition than soybean density. Farmers who rely on high mulch biomass for weed management may experience shifts in weed community composition toward an increased proportion of perennials and weeds with later emergence, heavier seeds, and shorter stature. However, increased soybean density reduced perennial weed biomass, making it a valuable complement to high cereal rye mulch biomass. As such, our research shows that weed management in organic no-till soybean is enhanced by multi-tactic weed management, which can enable synergistic weed suppression and management of diverse weed functional groups.