Role of soil adsorption and microbial degradation on dissipation of mesotrione in plant available soil water

Authors: Shaner, Dale; BRUNK, GALEN - Colorado State University; NISSEN, S - Colorado State University; WESTRA, P - Colorado State University; CHEN, W - Syngenta

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/5/2011
Publication Date: 1/1/2012
Citation: Shaner, D.L., Brunk, G., Nissen, S., Westra, P., Chen, W. 2012. Role of soil adsorption and microbial degradation on dissipation of mesotrione in plant available soil water. Journal of Environmental Quality. 41:170-178.

Interpretive Summary: Mesotrione is an important soil-applied herbicide for controlling weeds in corn. Understanding the factors in the soil that influence the dissipation of this herbicide is important. We conducted research to determine the role of soil properties and microbial activity on the dissipation of mesotrione in the soil and the plant available water (PAW). The study found that microbial degradation of mesotrione took place primarily in the PAW and the binding of the molecule to soil was dependent on soil organic carbon and pH. The dissipation potential of mesotrione in the PAW was very rapid with a half life of <2 days. However, the dissipation in the total soil-water system was slower due to the binding of the herbicide to the soil. The soil-bound phase serves as a reservoir to continuously release mesotrione to the PAW for microbial degradation while immobilizing the compound to potential leaching. This process correlation is important as it provides insight into how we can further develop efficient weed control practices that maximize product efficacy while minimizing potential off-target movement.

Technical Abstract: Mesotrione is a carotenoid biosynthesis-inhibiting herbicide labeled for pre-emergence and post emergent weed control in corn production. Understanding the factors that influence the dissipation of mesotrione in soil and in the plant available water (PAW) is important for both the environmental fate assessment and optimal weed management practices. The present research investigated the role of soil properties and microbial activities on the interrelated sorption and degradation processes of mesotrione in four soils by direct measurements of the PAW. Results showed that mesotrione bound to the soils time-dependently with approximately 14 days to reach equilibrium. The 24-hour batch equilibrium experiments provided the adsorption partition coefficient Kd ranging from 0.26 to 3.53 L kg-1 depending on soil organic carbon (OC) and pH. The dissipation of mesotrione in the soil-bound phase was primarily attributed to desorption to the PAW. Degradation in the PAW was rapid and primarily dependent on microbial actions with half-life (DT50) values <2 days in all four soils tested. The rapid liquid degradation became rate-limited by sorption as more available molecules were depleted in the soil pore water, resulting in a more slowed overall process for the total soil-water system (DT50<20 days). The dissipation of mesotrione in the PAW was due both to microbial metabolism and time dependent adsorption to the soils.