Dong Wang, Principal Investigator

Modeling Two-Dimensional Fumigant Gas Transport in Subsurface Soils and Volatilization Into the Atmosphere

Spatial distribution of air-phase concentration of 1,3-D at (a) 3 days, (b) 5 days, (c) 7 days, and (d) 10 days after application at 30 cm depth in a sandy loam soil.

The dynamics of pesticide volatilization are strongly controlled by subsurface transport and ambient environmental conditions, which may be described with process-based transport models. Application of simulation models can provide accurate characterization of fate and transport of volatile organic chemicals such as 1,3-dichloropropene and chloropicrin and their concentration dynamics that may be used as an index for pest control efficacy. But many parameters are often required for these types of mathematical models that translate to the initial and boundary conditions. Selection of a combination of sets of parameters optimized for better distribution uniformity and the least volatilization loss has a very practical value for field application by pesticide specialists and farm managers. This project integrates an existing comprehensive two-dimensional pesticide simulation model with management selections by adopting the most efficient numerical schemes.

During this research period, the group made significant progress towards modifying a two-dimensional pesticide transport model to simulate the distribution and volatilization of soil fumigants when applied through subsurface drip irrigation. The program provides a database with default soil and chemical properties to predict subsurface distribution patterns and potential surface volatilization losses of soil fumigants under a selected field configuration and application regimes. Up to three chemicals can be simulated simultaneously. Physical and chemical properties of cis- and trans-isomers of 1,3-dichloropropene and chloropicrin for a typical medium-textured soil were given as default values in the model input. Properties of other soil fumigants can be substituted as input options during program initialization, if some or all the parameters are known from laboratory or field measurements or other sources. A database containing hydraulic properties of twelve soil series (from clay to sand) were created as selectable sets of input values. Substitution is allowed if properties of an individual soil are known. The output includes a normalized run-time volatilization flux display and selections in post-processing. Output options from the post-processing program include data and graphs of cumulative volatilization loss, volatilization flux density, and concentration profile by time for a selected location or by location for a selected lapsed time after application.