<b>Fate of soil residual herbicides in cover cropping systems</b>
Creators: name: Maia, Lucas Oliveira Ribeiro
name: Johnson, William G.
name: Kladivko, Eileen J.
name: Armstrong, Shalamar D.
name: Young, Bryan G.
Publisher: name: Purdue University Graduate School
Year: 2024
Subjects: classificationCode: 300403
subject: Agronomy
classificationCode: 300401
subject: Agrochemicals and biocides (incl. application)

description: Cover crops and soil residual herbicides are some of the essential tools within the integrated weed management. When used at cover crop termination, residual herbicides can extend the period of weed control and reduce the selection pressure for herbicide resistance. However, previous research has indicated that the use of cover crops can increase the microbial activity of the soil which, in turn, is the primary route for herbicide degradation in the soil. In addition to the potential effect on the microbial breakdown of herbicides, cover crops can also alter the fate of herbicides by interception. Three field projects were established to (1) investigate the influence of cover crop [cereal rye (<i>Secale cereale</i> L.) and crimson clover (<i>Trifolium incarnatum</i> L.)] use on soil enzyme activities [β-glucosidase (BG) and dehydrogenase (DHA)], its effect on the concentration of residual herbicides (sulfentrazone, <i>s</i>-metolachlor, cloransulam-methyl, atrazine, and mesotrione) in the soil, and the interception of herbicides by cover crop residue; (2) to investigate the effect of cover crop termination strategies (fallow, standing, and roller crimped 1 d prior to application) and simulated rainfall volumes (0, 4.2, and 8.3 mm simulated over 20 min; equivalent to 0, 12.5, and 25 mm h<sup>-1</sup>) on atrazine wash off from cereal rye biomass onto the soil; (3) to investigate the effect of cereal rye termination strategies on the concentration of sulfentrazone, <i>s</i>-metolachlor, and cloransulam-methyl in the soil, weed control, and soybean [Glycine max (L.) Merr.] yield.Results from the first project suggests that the use of cover crops occasionally resulted in increased BG and DHA activities relative to the fallow treatment. However, even when there was an increase in the activity of these two enzymes, increased degradation of the residual herbicides was not observed. Furthermore, the use of cereal rye or crimson clover as cover crops did not reduce the efficacy of the residual herbicides in controlling weeds early in the growing season.In regards to the fate of atrazine after simulated rainfall, the results from the second project indicated that cereal rye biomass accumulation negatively impacted the amount of herbicide reaching the soil at the time of application. Although the roller crimped cereal rye reduced the amount of herbicide reaching the soil relative to the standing cereal rye, it also reduced atrazine leaching below the 0-5 cm of soil. Furthermore, in cover cropping systems with high levels of cereal rye biomass, more than 8.3 mm of rain are required to wash most of the atrazine off of the biomass.Lastly, the adoption of the planting green systems resulted in up to 84% interception of residual herbicides by the roller crimped cereal rye biomass. The use of cereal rye as cover crop did not improve the weed control relative to the fallow during the two years of field research. Soybean yield losses ranged from 10 to 44% with the adoption of the planting green system, primarily due to stand losses. However, there are strategies and proper equipment available that can be used to minimize soybean stand losses.