Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 28, 2007
Publication Date: March 3, 2008
Citation: Gao, S., T.J. Trout, S. Schneider. 2008. Evaluation of Fumigation and Surface Seal Methods on Fumigant Emissions in an Orchard Replant Field. J. Environ. Qual. 37:369-377. Interpretive Summary: Soil fumigation is important for successful orchard replanting. Fumigant application methods must be efficacious, cost-effective, and minimize emissions because profit margins for orchards are often small and high emissions can lead to human health risks. A field trial was established in fall 2005 to determine the effects of fumigation methods (shank-injection vs. drip-application) and surface treatments associated with water applications and plastic tarps (HDPE or VIF) on emissions of 1,3-dichloropropene (Telone) and chloropicrin (CP). Results indicate that soil water content is one of the most critical factors to control fumigant emissions. Pre-irrigated soil reduced emissions more than 50%. Water applications to soil surface prior or after fumigation were more effective than standard HDPE tarp to reduce emissions for both shank-injection and drip-application. Drip application of fumigants resulted in generally much lower emissions than shank-injections. As using water costs much less than plastic tarp and also does not have material disposal costs, practices with water applications can be developed in California orchards where micro-sprinkler irrigation systems are popularly used. However, further research needs to confirm the effectiveness of drip application on emission reductions as well as the impact on fumigation efficacy because of the large amount of water used that may affect fumigant diffusion in soil.
Technical Abstract: Pre-plant soil fumigation is an important management practice for controlling soil pests including nematodes and successful replanting in orchards. Reducing atmospheric emissions is necessary to minimize the detrimental environmental impact of fumigants. A field trial was conducted in fall 2005 in a peach orchard field. The objective was to investigate the effects of soil fumigation method (shank-injection vs. chemigation or drip-application) and surface treatments associated with water applications and plastic tarps on emissions of 1,3-dichloropropene (1,3-D) and chloropicrin (CP) from shank-injection of Telone® C-35 (61% 1,3-D and 35% CP) and drip-irrigation with InLine® (61% 1,3-D and 33% CP). Treatments included control (dry soil, no surface treatment), standard high density polyethylene (HDPE) tarp, virtually impermeable film (VIF) tarp, and pre-irrigation with shank-injection, and HDPE tarp and water caps (pre- and post-water applications using micro-sprinklers) with drip-application. The highest 1,3-D and CP emission losses were from the control (36% and 30% for 1,3-D and CP respectively) and HDPE tarp (43% and 17% for 1,3-D and CP, respectively) over shank-injection for a two week monitoring period. The pre-irrigation that produced a moist soil profile (at 30-50% field capacity level) and VIF tarp over shank-injection had similar total emission losses (19% for 1,3-D, and 8-9% for CP). The HDPE tarp and water caps over drip-application treatments resulted in the lowest emission losses (12-13% for 1,3-D and 2-3% for CP). Lower fumigant concentrations in the soil-gas phase were observed in the drip-applications than shank-injection treatments. All fumigated treatments, however, provided 100% kill to citrus nematodes in bags buried from 30 to 90 cm depth. The results indicate that pre-irrigation with a moderate amount of water, drip-application methods combined with HDPE tarp or water applications may be effective ways to reduce emissions of 1,3-D and CP. Further work is needed to optimize practices that reduce emissions while maximizing fumigant efficacy.