Submitted to: Environmental Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/30/2006
Publication Date: 10/7/2006
Citation: Yates, S.R. 2006. Simulating herbicide volatilization from bare soil affected by limited solubility in water. Environmental Science and Technology. Vol 40:6963-6968 Interpretive Summary: Several monitoring studies have shown that agricultural use of pesticides can contaminate air and water resources. Past research has shown that pesticide movement in soils is affected by many interrelated factors such as the pesticide application methods, soil and environmental conditions, and water management practices. A numerical model was developed to predict the behavior of a pre-emergent herbicide, triallate, after application to a field soil. The model simulates pesticide fate and transport in soil, movement as a vapor, and emissions from the soil surface into the atmosphere. A field experiment (previously reported) was conducted to measure the volatilization rate of triallate after application to a bare soil. These measurements were used to compare to the model’s performance. The measured total emission was 31% and the predicted values varied from 21 % to 36% depending on the detail included in the simulation. A prospective simulation over a period of 100 days indicated that applying triallate to the soil surface would ultimately lead to emissions of 80% but incorporating triallate to depth of 10 cm would reduce emissions to less than 5%. Further, after 100 days, incorporation leads to soil concentrations of 41% compared to 6% when the triallate was surface applied. Improved efficacy and environmental protection results from incorporation of triallate into the soil surface.
Technical Abstract: A numerical model was developed to predict the behavior of triallate after application to a field soil. The model simulates pesticide fate and transport in soil, movement in the vapor phase and volatilization from the soil surface. The model has options to allow water and/or heat transport and can limit simulated aqueous phase concentrations to herbicide solubility in water. Several methods for describing the volatilization boundary condition were used to assess the accuracy in predicting the triallate volatilization, including a stagnant boundary layer model that requires no atmospheric information and a boundary condition that couples soil and atmospheric processes. For some information, such as cumulative emissions, all the model tests provided relatively similar results and indicate that simplified modeling conditions may be appropriate to obtain certain information. The measured total emission was 31% and the predicted values ranged from 21 % to 36%. A prospective simulation over a period of 100 days indicated that applying triallate to the soil surface would ultimately lead to emissions of 80% of the applied material and soil concentrations of 6%. Incorporating triallate to depth of 10 cm would reduce emissions to less than 5% and lead to soils concentrations to 41%.