Cover Crop Management Practices to Improve Soil Health and Weed Suppression in Cropping Systems

Abstract

Introducing integrated crop-livestock systems into row crop production may provide incentives for producers to plant cover crops and promote soil health benefits on degraded soils of the southeastern United States, but effects of these practices on crop yields and soil health in coastal plain soils are not well established. A four-year study was established at the Wiregrass Research and Extension Center in Headland, Alabama to test the effects of different grazing regimes on soil health and crop productivity. Three cattle grazing regimes (mid-February, mid-March, and mid-April cattle removal dates) and an non-grazed control were included in a randomized complete block design and replicated three times. Chemical soil health indicators (soil organic carbon, permanganate oxidizable carbon), physical soil health indicators (water stable aggregates, penetration resistance), biological soil health indicators (microbial biomass carbon, arbuscular mycorrhizal fungi colonization), crop yield, and cover crop biomass were evaluated. Cover crop biomass at termination was reduced for all grazed treatments compared to the non-grazed control, and the mid-March and mid-April treatments resulted in the lowest amount of cover crop biomass. No treatment effects were observed for arbuscular mycorrhizal fungi, microbial biomass carbon, and permanganate oxidizable carbon. Soil organic carbon was higher in the non-grazed treatment than the mid-April grazing treatment for the 0-30 cm depth. Penetration resistance at the 0-50 cm depth and water stable aggregates at the 0-30 cm depth were both negatively impacted by increased grazing period lengths. Results from this study suggest that longer cover crop grazing periods have little effect on biological and chemical soil health indicators in the short term but can negatively impact some physical soil health indicators. Shorter grazing periods allowed for regrowth of cover crop biomass, leaving more residues to prevent soil erosion and reduce soil compaction. Control of herbicide resistant weeds is a growing problem for southeastern row crop producers. Utilizing alternative programs that integrate winter cover crops with postemergence herbicides may be an effective form of weed management. Field studies were conducted at the Tennessee Valley Research and Extension Center in Belle Mina, AL in 2022 and 2023 and at the E.V. Smith Research Center in Shorter, AL in 2023. An experiment using a 2x2x3 factorial design with 4 replications was used to evaluate the ability of different cover crop management practices in conjunction with preemergence herbicides for weed suppression in soybeans (Glycine max). Main factors were two seeding rates of a cereal rye + crimson clover mixture, two cover crop nitrogen fertilization rates, and three preemergence herbicide treatments (untreated, S-metolachlor, acetochlor) applied to soybeans at planting. Cover crop biomass was collected to observe the effects of seeding and fertilization rates on aboveground biomass production. Weed counts were conducted ~14, 28, 42, and 56 days after soybean emergence in two, 1 m2 areas within each plot. Common weed species observed were large crabgrass (Digitaria sanguinalis), Palmer amaranth (Amaranthus palmeri), prickly sida (Sida spinosa), barnyardgrass (Echinochloa crus-galli) and morningglories (Ipomoea spp.). Cover crop biomass (P=<0.0001), herbicide treatment (P=<0.0001) and herbicide x time interaction (P=<0.0001) all had a significant effect on weed emergence. Weed emergence was lower for the S-metolachlor and acetochlor treatments compared to the no herbicide treatment. A negative linear correlation (R2=0.1327) was observed between cover crop biomass produced and weed emergence. Weed emergence increased over time but preemergence herbicides were able to decrease emergence below levels observed in the non-treated at ~42 DAP. This data suggests that cover crop biomass and preemergence herbicides can help to suppress early season weed emergence in soybeans.