Location: Crops Pathology and Genetics Research2011 Annual Report
1a. Objectives (from AD-416)
This project is designed to provide data that will facilitate effective use of “totally impermeable” film (TIF) to reduce fumigant emissions from soil. Air and soil concentrations of fumigant will be examined and modeled spatially and temporally to formulate appropriate tarp cutting times after application of fumigants. The specific objectives are: 1) Determine the best tarp cutting time for fields fumigated with 1,3-dichloropropene and chloropicrin under TIF. 2) Determine fumigant concentration change and distribution in soil profiles down to 1 m depth under the TIF. 3) Generate data on the fumigant emissions using dynamic flux chambers. 4) Determine residual fumigant concentration in soil at the time of tarp cutting to facilitate estimation of potential VOC loss thereafter. 5)Generate the data on the permeability of the plastic film (VaporSafeTM) used in this study for the active ingredients 1,3-dichloropropene and chloropicrin.
1b. Approach (from AD-416)
Objective 1-accumulate fumigant emissions data from ambient air around three large fields treated by broadcast shank fumigation in Ventura County. The test system will use methods preferred by California Department of Pesticide Regulation (CDPR) for assessing potential chloropicrin and 1,3-dichloropropene emissions from field applications. Objective 2-Fumigant concentration changes and movement in soil profile will be monitored throughout the study. A total of four soil-gas sampling probes will be installed in each field: two at the shank line and two between shank lines. Objective 3-Soil samples for residual fumigants by the time of tarp-cutting will be collected for evaluation of fumigant fate. Soil water content and temperature will be measured in the soil samples to facilitate required concentration calculations. Objective 4-The mass transfer coefficient (MTC) will be determined for the TIF using the standardized method (Papiernik et al. 2001; Yates et al., 2008). This method uses static sealed cells, where fumigant vapor is spiked to one side of the film and the concentrations on both side of the film are monitored until equilibrium, or, in the case of very-low-permeability films, at least until valid regression curves can be estimated based on adequate sampling at various pre-determined intervals.
3. Progress Report
Established in support of Obj.4, the goal being to assess & demonstrate emissions reduction technologies & strategies for fumigant alternatives to MB. The goal of this project is to provide data that will facilitate effective use of "totally impermeable" film(TIF)to reduce fumigant emissions from soil. Two fields located near each other were chosen to ensure that meteorological conditions, soil type, & soil temperature were similar in each field. Both applications were conducted on the same day using the same application rig. Air monitoring was conducted concurrently at each field starting with the beginning of application & continuing for 13days. The applications were made to two 1-acre fields located near Oxnard, CA(09/10/09). Fields were separated by several miles to prevent cross-contamination. Air sampling was conducted starting with the beginning of each application and continued through 09/23/09. An experimental 50/50 mixture of chloropicrin and 1,3-D was used on both fields. The application method, injection depth and target application rates were:(Field#1) shank, broadcast, tarped(10.5-ft wide, 1-mil, standard polyethylene film); 12-in. injection, 280lbs/acre; and (Field#2)shank, broadcast, tarped(1-mil, EVAL-resin barrier film), 12-in. injection, 280lbs/acre. Quantitative data on airborne concentrations of chloropicrin and 1,3-D resulting from applications were used to estimate the potential for exposure to persons near treated fields. Flux values were determined using ISCST. These data are used by regulatory agencies in preparing risk assessments & in evaluating emission reduction efforts. For Field#1(polyethylene tarp), the chloropicrin peak flux rate was 8.31 µg m-2 s-1 at 162-168hrs after the start of application. For Field#2(EVAL-resin barrier tarp), the chloropicrin peak flux rate was 4.62 µg m-2 s-1 at 0-6hrs after the start of application. Total mass loss of chloropicrin was 10.8%(Field#1-polyethylene tarp)and 14.1%(Field#2-EVAL-resin barrier tarp). The interval-specific peak and highest 24-hr average concentration for 1,3-D are summarized below for each field, where the 24-hr average is commonly used by regulatory agencies for assessing bystander exposure risk to 1,3-D. For Field#1(polyethylene tarp), the 1,3-D peak flux rate was 38.28 µg m-2 s-1 at 30-36hrs after the start of application, and the highest 24-hr average concentration was 23.86 µg m-2 s-1 at 12-36hrs after the start of the application. For Field#2(EVAL-resin barrier tarp), the 1,3-D peak flux rate was 28.53 µg m-2 s-1 at 144-150hrs after the start of application, and the highest 24-hr average concentration was 15.46 µg m-2 s-1 at 144-168hrs after the start of the application. Total mass loss of 1,3-D was 43.24%(Field#1-polyethylene tarp) and 42.9%(Field#2-EVAL-resin barrier tarp). This project determined that tarp cutting time should be increased to avoid potential large spikes of 1 3-D after 5 days. Further studies are needed to determine appropriate tarp cutting time. The project is monitored by maintaining a complete file of the agreement, reviewing the annual reports, & conducting meetings with the cooperator during the course of the agreement.