Evaluating surface seals in soil columns to mitigate methy isothiocyanate volatilization

Authors: NELSON, SHAD - Texas A&M University; SIMPSON, CATHERINE - Texas A&M University; AJWA, HUSEIN - University Of California; Williams, Clinton

Submitted to: Integrated Pest Management and Pest Control
Publication Type: Book / Chapter
Publication Acceptance Date: 7/27/2011
Publication Date: N/A
Citation: N/A

Interpretive Summary: The banning of methyl bromide (MeBr) as a pre-plant soil fumigant due to its implication as an ozone depleting substance, has led to increased interest in finding alternative soil fumigants to replace MeBr. A promising alternative to methyl bromide is metam sodium which produces the active compound methyl isothiocyanate (MITC). To prevent volatile looses of MITC from the soil the use of a water seal has been proposed. A 3.8-cm water seal provided increased retention of MITC within the soil profile, along with the greatest suppression of MITC volatilization from the soil surface and the longest retention of MITC within the soil profile.

Technical Abstract: The banning of methyl bromide (MeBr) as a pre-plant soil fumigant due to its implication as an ozone depleting substance, has led to increased interest in finding alternative soil fumigants to replace MeBr. One of the promising alternatives for certain crops is methyl isothiocyanate (MITC) generating compounds, such as metam sodium. The physiochemical characteristics of MITC are significantly different than that of MeBr, such that its effectiveness in regards to dissipation and movement in the soil is altered by multiple factors, such as soil type, texture, and soil moisture content. The largest challenge to soil fumigation is the prevention of fumigant loss to the atmosphere and especially so to nearby communities and homes adjacent to farm land. Rapid off-gassing or non-target release of the fumigant to the atmosphere can lead to poor pesticide performance and ineffective pest control. To combat this problem that is common to all soil fumigants currently on the market, various methods have been employed to reduce chemical off-gassing. A few of these methods are tarping the soil surface immediately following chemical application with high density polyethylene plastic, incorporation of organic matter to the soil surface to absorb the fumigant or altering chemical formulations. Another method of reducing fumigant loss can be applying a surface water application as a means of sealing the soil surface to prevent chemical volatilization. On-farm field scale studies have been performed to evaluate all of these methods to better evaluate the potential for reducing fumigant loss to the atmosphere. However, field-scale studies are expensive to perform and challenging to control experimental error and replicate due to diurnal temperature fluctuations, varying soil physical properties, and air current differences. Thus, the volatilization loss in one study, will not represent the typical fumigant loss from site to site. A more controlled laboratory study is needed to more adequately predict fumigant loss under specific conditions. Laboratory-scale soil columns can be used to study soil fumigant release from soils under a wide array of conditions and under controlled conditions. The aim of this study was to evaluate the amount of water applied to the surface of a specific soil type would reduce MITC volatilization in soil columns. Furthermore, evaluating the impact that varying soil physical properties have on MITC loss, such as varied soil type, soil bulk density, organic matter additions, and various MITC generating compound formulas have on MITC loss and mitigation. In short, the results of these studies will summarize the effectiveness of the use of soil columns to adequately assess MITC loss at the laboratory scale as a tool to predict chemical fate prior to the expense of large-scale on-farm studies.