Cover crop residue components and their effect on summer annual weed suppression in corn and soybean

Abstract

Cover crop residue can act as a mulch that will suppress weeds, but as the residue degrades, weed suppression diminishes. Biomass of cover crop residue is positively correlated to weed suppression, but little research is available regarding the composition of cover crop residue and its effect on weed suppression. Field experiments were conducted to determine the impact of cover crop residue properties (i.e., total carbon, total nitrogen, lignin, cellulose, and hemicellulose) on summer annual weed suppression and cash crop yield. Cover crop monocultures and mixtures were planted in the fall and designed to provide a range of biomass and residue properties. Cover crops were followed by corn (Zea mays L.) or soybean [Glycine max (L.) Merr.]. At termination, cover crop biomass and residue components were determined. Biomass ranged from 3,640 to 8,750 kg ha−1, and the carbon-to-nitrogen (C:N) ratio ranged from 12:1 to 36:1. As both cover crop biomass and C:N ratio increased, weed suppression and duration of suppression increased. For example, a C:N ratio of 9:1 is needed to suppress redroot pigweed (Amaranthus retroflexus L.) 50% at 4 wk after termination (WAT), and that increases to 16:1 and 20:1 to have 50% suppression at 6 and 8 WAT, respectively. Similarly, with biomass, 2,800 kg ha−1 is needed for 50% A. retroflexus suppression at 4 WAT, which increases to 5,280 kg ha−1 and 6,610 kg ha−1 needed for 50% suppression at 6 and 8 WAT, respectively. In general, similar trends were observed for pitted morningglory (Ipomoea lacunosa L.) and large crabgrass [Digitaria sanguinalis (L.) Scop.]. Corn and soybean yield increased as both cover crop biomass and C:N ratio increased where no weed control measures were implemented beyond cover crop. The same trend was observed with cash crop yield in the weed-free subblocks, with one exception. This research indicates that cover crop residue composition is important for weed control in addition to biomass.

Influence of Cereal Rye Management on Weed Control in Soybean

“…Cover crops allowed to advance to the late-vegetative or early-reproductive stages produce significantly more biomass. In addition, the cover crop tissue contains a higher C:N ratio that resists decomposition and allows the dead biomass to persist longer (Wagger et al, 1998;Pittman et al, 2020).…”

Cover crops and preemergence herbicides: An integrated approach for weed management in corn-soybean systems in the US Midwest

“…Previous research conducted in Wisconsin organic soybean production with a greater cereal rye seeding rate and delayed cereal rye termination until after the boot growth stage, indicates that there is potential to produce cereal rye biomass of 4.30-10.80 Mg ha -1 (Bernstein et al, 2011;Vincent-Caboud et al, 2019). Greater amounts of cereal rye biomass accumulation prior to crop planting have been observed in previous studies with 2.05-3.25 Mg ha -1 in Maryland (Otte et al, 2019), 7.39 Mg ha -1 in Virginia (Pittman et al, 2020), 4.97 Mg ha -1 in South Carolina (Norsworthy, 2004), 2.20-6.10 Mg ha -1 in Illinois (Ruffo et al, 2004), and 1.15-2.89 Mg ha -1 in Missouri (Cornelius and Bradley, 2017). The warmer spring growing conditions at these locations are favorable for a cereal rye cover crop to accumulate more biomass prior to the typical time of crop planting when compared to covers grown in the Upper-Midwest U.S. (Kukal and Irmak, 2018).…”

Tarping Cover Crops Facilitates Organic No-till Cabbage Production and Suppresses Weeds

“…Some authors have proposed that lower biomass levels (e.g., 5-6 MgÁha À1 ) may be sufficient in northern latitudes (Wallace et al, 2017), but data are lacking to develop thresholds. Furthermore, weed species vary in their response to cover crop biomass and residue composition (Pittman et al, 2020;Teasdale and Mohler, 2000). The relatively low biomass in our experiment was likely a result of low GDDs as well as extremely low precipitation in May in year 2.…”

“…The effects of tarping on weed community composition and diversity indicate that tarping, like tillage, can act as a strong filter on weed community assembly (Birthisel and Gallandt, 2019). Variability in how different weed species respond to levels and quality of cover crop mulch (Pittman et al, 2020;Teasdale and Mohler, 2000) show that cover crop mulch itself has a filtering effect on weed community assembly. Our data suggest that although most weed species present were suppressed by tarping cover crops (i.e., combining the two filters of cover crop mulch and tarps), some were more capable than others of "passing through" these filters, including A. retroflexus.…”