Foliar dicamba application has no lasting effects on microbial activities in the soybean rhizosphere

Authors: Tyler, Heather

Submitted to: American Journal of Plant Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/15/2020
Publication Date: 11/18/2020
Citation: Tyler, H.L. 2020. Foliar dicamba application has no lasting effects on microbial activities in the soybean rhizosphere. American Journal of Plant Sciences. (11):1706-1713. https://doi.org/10.4236/ajps.2020.1111122.
DOI: https://doi.org/10.4236/ajps.2020.1111122

Interpretive Summary: Corn, soybean, and cotton varieties engineered with resistance to the herbicide dicamba have been introduced to provide alternative weed control options for farmers to combat the widespread proliferation of glyphosate resistant weeds. However, little is known about how the new herbicide formulations released with these crops impact the activities of microorganisms in soil that play pivotal roles in nutrient cycling, particularly in the rhizosphere where they are most likely to be impacted through altered root exudation in response to herbicide treatment. A scientist from the USDA-ARS Crop Productions Systems Research Unit in Stoneville, MS conducted a greenhouse study examining the effects of two dicamba formulations on microbial activities in the rhizosphere of resistant soybean plants. Activities linked to carbon and phosphate cycling were not affected by dicamba application, while an enzyme linked to nitrogen mineralization was temporarily depressed in the rhizospheres of plants treated with either dicamba formulation. However, the levels of this enzyme recovered to non-treated levels three days after herbicide treatment. These results suggest that growers can use these formulations without incurring long-term detrimental effects on microbial activities in the soil of soybean field.

Technical Abstract: The proliferation of glyphosate resistant weeds has resulted in significant losses in productivity of crops such as corn, soybean, and cotton. As a result, new crop varieties with resistance genes from other herbicides, such as 2,4-D and dicamba, have been developed as part of alternative weed control cropping systems. However, little is known about how application of these herbicides impacts the microorganisms that carry out nutrient cycling in soil of these cropping systems, particularly in the rhizosphere, the soil compartment immediately adjacent to the root system which is pivotal to plant nutrient uptake. The purpose of the current study was to assess the effects of dicamba on soil enzyme activities linked to C, N, and P cycling in the rhizosphere of resistant soybean plants. While dicamba had no significant effects on the activities of enzymes linked to C or P cycling in the rhizosphere, N-acetylglucosaminidase activity was temporarily inhibited, but recovered by three days after application. These results suggest there are no long-lasting negative effects of dicamba in the rhizosphere of treated plants when applied at field rates.