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Title: 1,3-dichloropropene and chloropicrin emissions following simulated drip irrigation to raised beds under plastic films

item Ashworth, Daniel
item LUO, LIFANG - University Of California
item XUAN, RICHENG - University Of California
item Yates, Scott

Submitted to: Environmental Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/10/2010
Publication Date: 8/1/2010
Citation: Ashworth, D.J., Luo, L., Xuan, R., Yates, S.R. 2010. 1,3-dichloropropene and chloropicrin emissions following simulated drip irrigation to raised beds under plastic films. Environmental Science and Technology. 44(15):5793-5798.

Interpretive Summary: Agricultural fumigants are used to kill a wide variety of soil pests (e.g. nematodes, fungi, weeds) prior to planting crops. As a gas, these fumigants can be released form the soil into the atmosphere where they are a health/environmental concern. In addition to direct inhalation by humans, they can also lead to the formation of photochemical smog. Using a laboratory approach, we assessed whether this release could be reduced by applying the two fumigants (1,3-dichloropropene (1,3-D) and chloropicrin (CP)) with a large quantity of water (drip application) and covering the soil with plastic film. Two types of plastic film were used, high density polyethylene (HDPE) and virtually impermeable film (VIF). VIF reduced emissions of both fumigants when compared to the HDPE. We then compared the results to existing data for a more conventional application procedure (injecting the fumigants at around 30 cm depth without water). This comparison suggested that the drip application did reduce emission of the fumigants. However, when we compared the data to our previous results for a conventional 30 cm injection using the same soil and same plastics, the drip application did not consistently reduce emissions. In some cases emissions were increased. Therefore, we believe that further comparisons between the two types of application, preferably using the same soil and plastic, are required. Development of simple but accurate methods to estimate fumigant emissions will help regulators and users to protect the environment while maintaining agricultural production.

Technical Abstract: Using laboratory soil chambers a non-scaled representation of an agricultural raised bed was constructed. For a sandy loam soil, a drip application of 1,3-dichloropropene (1,3-D) and chloropicrin (CP) under both high density polyethylene (HDPE) and virtually impermeable film (VIF) was performed at 5 cm soil depth. Soil gas distribution of the fumigants, together with emissions into the headspace above the bed, sidewall and furrow were determined over time. Total emissions from the HDPE treatment were: cis 1,3-D 32%; trans 1,3-D 29 % and CP 8 %. Due to its greater impermeability, the values for VIF were: 15 %; 8 % and 1%, respectively. With HDPE, the majority of the emissions occurred from the bed, whilst for VIF the majority of the emissions were from the furrow. Compared to a range of literature values for shank injection, the use of drip application appears to offer a benefit in reducing 1,3-D and CP emissions. However, perhaps the most accurate comparison is with our previous data for shank injection to the same soil and using the same plastic films (Ashworth et al., 2009). In this comparison, only 1,3-D emissions under HDPE were lower in the drip application treatments; 1,3-D emissions under VIF and CP emissions under both films were greater with the drip application.