Location: Water Management Research2013 Annual Report
1a. Objectives (from AD-416):
To develop efficient and cost-effective field management practices to minimize emissions of methyl bromide alternative fumigants from pre-plant soil fumigation while achieving effective pest control.
1b. Approach (from AD-416):
Field management methods that have potential to reduce fumigant emissions and improve efficacy will be tested. Methods including fumigant application (new shank design, and drip. vs. shank application), low permeable tarps, irrigation, and soil amendment with organics as well as combination of these methods will be determined for their effectiveness and feasibility. Field trials will be conducted in air-quality non-attainment areas in California including Ventura County and the San Joaquin Valley. Data on emission rates, total emission losses, distribution of fumigants in soil profile and efficacy on soil pest control will be collected. Monitored data will be summarized to identify good and effective practices that can be adopted in growers’ fields.
3. Progress Report:
This project contributes to meeting objective 5: Develop various application methods, soil amendments, and physical barriers to reduce the emissions and enhance efficacy of the chemical alternatives to methyl bromide. This is the final report of the agreement. Under the agreement, collaborative research has been conducted towards developing agricultural management or practices to reduce emissions of soil fumigants. There are five air quality nonattainment areas (NAAs) for ozone in California including Ventura County and the San Joaquin Valley. Emission reduction from soil fumigation is demanded for these NAAs. Two large field trials were conducted to collect data to assist in regulatory decision making on the use of low permeability tarps in soil fumigation. The first trial was conducted near Oxnard in 2009 in Ventura County and the second trial was conducted near Lost Hills in Kern County in 2011. The 2009 field trial near Oxnard compared standard polyethylene (PE) tarp and totally impermeable film (TIF) tarp on emission reduction and fumigant concentration change under the tarp as well as distribution in the soil profile. Two fields (one acre each) were fumigated with a 50/50 mixture of 1,3-dichloropropene (1,3-D) and chloropicrin (CP) through shank injection to 12 inch depth and a 12 inch spacing between injection lines at the same rate (~280 lb/acre) but tarped with the different films. The 2009 field trial was to compare differences between the new TIF tarp and standard PE tarp in emission and fumigant changes in soil. The 2011 field trial included three large fields that were fumigated with a mixture of 40:60 1,3-D:CP at ~590 lb/acre using the same fumigant application method as in the 2009 trial. All fields were tarped with TIF immediately following fumigant injection, but with different tarp-cutting times (5, 10, and 16 days for the 2, 2, and 8 acre field size, respectively). The 2011 trial was to collect information on how TIF tarp can be safely used to avoid emission spikes following tarp-cutting. For both field trials, emission was monitored continuously with dynamic flux chamber method as well as aerodynamic modeling approach. ARS researchers were in charge of collecting data on emissions directly from the tarped field and also on soil fumigant fate and distribution or transport in soil. Collaborators were in charge of collecting data for aerodynamic modeling on emission estimates from the whole field. This project was monitored by regular site visits and regular phone calls or e-mails between ARS and the University investigators on this project. Results from the 2009 field trial show that TIF can be extremely effective in reducing fumigant emissions compared to the PE tarp. Much higher concentrations and more uniform distribution of fumigants were observed under TIF, which can lead to improved efficacy and/or using reduced fumigant rates in comparison with the standard PE film. Upon tarp-cutting after a 6-d covering period, however, surges of emissions occurred with much higher emission rates from the TIF-tarped field than the PE-covered field. Thus, a longer waiting period for the tarp-cutting is required to reduce potential exposure risks. This research provided first-hand information on emission reduction using the TIF tarp in large field applications. The 2011 trial data show that with a TIF tarp on the field low emission flux was continuously measured throughout 16 days of tarp-covering period with a total emission loss <10% from the tarped field and < 1% at the tarp edges. Emission flux upon tarp-cutting after 16 days of fumigant application increased, but was substantially lower than the 6 days of tarp covering determined in the 2009 field trial. Data on fumigant distribution and changes over time in soil were used by the regulatory agency, California Department of Pesticide Regulation, to develop modeling methodology for estimates of fumigant emissions under various fumigation conditions. This study demonstrated the ability of TIF to significantly reduce fumigant peak flux, decrease total emission loss, and the required longer tarp-covering periods. In 2013, results from 2009 field trial and 2011 field trial were summarized. Two manuscripts were submitted to California Agriculture and both manuscripts were accepted for publication.