Impact of 2,4-D and glyphosate on soil enzyme activities in a resistant corn cropping system

Authors: Tyler, Heather

Submitted to: Agronomy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/2/2022
Publication Date: 11/5/2022
Citation: Tyler, H.L. 2022. Impact of 2,4-D and glyphosate on soil enzyme activities in a resistant corn cropping system. Agronomy. https://doi.org/10.3390/agronomy12112747.
DOI: https://doi.org/10.3390/agronomy12112747

Interpretive Summary: Crops with resistance to multiple herbicides have been developed to provide farmers with more weed control options. These new crop varieties include those with resistance to both glyphosate and 2,4-dichlorophenoxyacetic acid (2,4-D). However, both these herbicides have the potential to impact soil microorganisms involved in nutrient cycling, and there is concern that co-application of these herbicides may have a greater effect on microbial enzyme activities involved in nutrient cycling than when they are applied separately. Scientists at the USDA-ARS Crop Productions Systems Research Unit in Stoneville, MS conducted a two-year field study examining the effects of 2,4-D alone and 2,4-D+glyphosate on microbial activities in both bulk and rhizosphere soil in corn fields. 2,4-D+glyphosate slightly increased activities of enzymes associated with carbon, nitrogen, and phosphate processing in bulk soil at some timepoints. These effects occurred mainly in the upper layer of bulk soil, and were inconsistent between years, while no differences in activity were noted in the rhizosphere soil associated with corn roots. These results indicate that 2,4-D and glyphosate applied together do not have long lasting or negative effects on soil microbial activities in corn fields.

Technical Abstract: Crop varieties resistant to multiple herbicides have been developed to provide better control of weed populations in row crop fields where glyphosate resistance has become common. These new varieties include lines of corn (Zea mays) resistant to both glyphosate and 2,4-D-dichlorophenoxyacetic acid (2,4-D). As these herbicides have the potential to impact microbial communities in soil, there is concern that their co-application may have a greater effect on soil activities linked to soil nutrient cycling than if they were applied individually. To investigate this possibility, a field study was conducted on 2,4-D+glyphosate resistant corn to determine the impact of 2,4-D alone and 2,4-D+glyphosate on extracellular enzyme activity in both bulk and rhizosphere soil. Corn was treated at the V2 and V8 developmental stages. Responses of soil activities were small in magnitude and inconsistent between timepoints. 2,4-D+glyphosate treated plots had higher beta-glucosidase, cellobiohydrolase, and phosphatase activities, but only after the V2 application in bulk soil in the first year of the study, while no significant effects were observed in the rhizosphere. Enzyme activities were more impacted by soil organic matter than herbicide treatments. These results suggest that when applied at label rates, 2,4-D+glyphosate application will not adversely affect soil microbial enzyme activities.