1a.Objectives (from AD-416):
1) Determine emission reductions by the TIF from fumigation in deep-rooted orchard soils.
2) Determine reduced fumigant application rates that still achieve sufficiently high fumigant concentration and uniform distribution in soils for ensuring good efficacy from broadcast injection under the TIF tarp.
3) Determine the proper waiting period between fumigation and tarp-cutting by evaluating fumigant degradation rates in orchard representative soil types, temperature and soil moisture conditions in the San Joaquin Valley.
1b.Approach (from AD-416):
Two field trials and laboratory experiments are planned to achieve the study objectives during a two year period. A field trial will be conducted to determine emission reduction and soil-gas fumigant concentration/distribution at full and reduced rates under TIF tarp in deep-rooted orchard soils. A standard PE film will be used as a comparison. Alternatives to MeBr will be used such as Telone C35 or Telone II. A second trial in the 2nd year will test either for a different alternative fumigant product (e.g., methyl iodide if registered in CA) or a different orchard soil to repeat the 1st year’s treatments to verify findings depending on the 1st year’s data. Laboratory incubation experiments will be conducted simultaneously to determine the degradation or dissipation rate of fumigants in soil that assist in determining proper waiting period for TIF tarp-cutting to avoid a surge of emissions.
This project supports objective 3 of the parent project. This is the second year of a 2-year project and all objectives are met. Emission reduction by totally impermeable film (TIF) tarp and fumigant distribution in soil from full rate and reduced rate was measured in a field trial. See reports under Project 5302-13220-004-26R. The laboratory component of this project was to determine the degradation rate of several important fumigants as a function of application rates. These experiments were to test the hypothesis; fumigant degradation rates decrease as the amount of fumigant increases in soil, which simulates the scenario occurring under a low permeability tarp. The information is useful in determination of effective but reduced rates. Degradation characteristics of several fumigants including 1,3-dichloropropene, chloropicrin, and dimethyl disulfide at application rates ranging from 10 to 200 mg/kg in five soils. Data show the degradation of these fumigants is highly dependent on both the chemical and application rate in a soil and also vary among soils. Fumigant degradation rates decrease significantly with the increase of application rates of chloropicrin and dimethyl disulfide, but much smaller changes are observed for 1,3-dichloropropene isomers at all rates tested. These findings indicate that in order to determine an effective fumigant application rate under low permeability tarps, variation in fumigant degradation rates is an important factor to consider.