Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/1/2004
Publication Date: 11/1/2004
Citation: Guo, M., Zheng, W., Papiernik, S.K., Yates, S.R. 2004. Distribution and leaching of methyl iodide in soil following emulated shank and drip application. Journal of Environmental Quality. 33:2149-2156. Interpretive Summary: Soil fumigation is used to control soil-borne pests and pathogens in soils to be planted to high-cash-value crops. Methyl iodide (MeI) is a promising chemical alternative to methyl bromide, which is being phased out worldwide due to its potential to deplete stratospheric ozone. The pest-control efficacy and ground water contamination risks of MeI as a fumigant are highly related to its gas-phase distribution and leaching after soil application. In this study, we investigated the distribution and leaching of MeI in soil following two different application methods: shank injection and subsurface drip application. Relative to shank injection, drip application inhibited diffusion (resulting in significantly lower concentrations in the soil air that could adversely impact pest control), leaching (potentially reducing the threat of ground water contamination), and retention of persistent residues of MeI. These results suggest that soil fumigation with MeI may pose a risk of ground water contamination in vulnerable areas. The loss of methyl bromide as a soil fumigant represents a critical economic and controversial global environmental issue. The identification and development of safer alternatives is crucial to the continued use of soil fumigation in American agriculture. Methyl iodide is currently in registration review and is expected to serve as a major replacement for methyl bromide. The MeI registrant and extension professionals will use these results to develop management practices for this new soil fumigant that will decrease the risk of water and air contamination while maximizing pest control efficacy.
Technical Abstract: Methyl iodide (MeI) is a promising alternative to methyl bromide in soil fumigation. The pest-control efficacy and ground water contamination risks of MeI as a fumigant are highly related to its gas-phase distribution and leaching after soil application. In this study, the distribution and leaching of MeI in soil following shank injection and subsurface drip application were investigated. Methyl iodide (200 kg ha**-1) was directly injected or drip applied at 20-cm depth into Arlington sandy loam (coarse-loamy, mixed, thermic Haplic Durixeralfs) columns (12-cm i.d., 70-cm height) tarped with virtually impermeable film. Concentration profiles of MeI in the soil air were monitored for 7 d. Methyl iodide diffused rapidly after soil application, and reached a 70-cm depth within 2 h. Relative to shank injection, drip application inhibited diffusion, resulting in significantly lower concentration profiles in the soil air. Seven days after MeI application, fumigated soil was uncapped, aerated for 7 d, and leached with water. Leaching of MeI was significant from the soil columns under both application methods, with concentrations >10 µg L**-1 in the early leachate. The leaching was greater following shank injection than drip application, with an overall extent of 33 g ha**-1 for shank injection and 19 g ha**-1 for drip application. Persistent residues of MeI remaining in soils after leaching were 50 to 240 ng kg**-1, and the contents were slightly higher following shank injection than drip application. The results suggest that fumigation with MeI may pose a risk of ground water contamination in vulnerable areas.