Submitted to: Journal of Environmental Quality
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/13/2005
Publication Date: 8/9/2005
Citation: Zhang, Y., Spokas, K.A., Wang, D. 2005. Degradation of methyl isothiocyanate and chloropicrin in forest nursery soils. Journal of Environmental Quality. 34:1566-1572. Interpretive Summary: Chemical soil fumigation is a means of controlling weed and plant pathogens by the use of chemicals. The use of chemical fumigation for weed control is particularly prevalent in southern US forest nurseries. However, recently studies in agricultural soils have shown enhanced degradation potential of applied agrochemicals with sequential applications. This study investigated enhanced degradation potential in forest nursery soils and found that degradation rates of the tested fumigants were related to nursery fumigation history, application rates, and freshness of tested soils. However, there were no significant differences seen in degradation rates of fumigated and non-fumigated forest soils, suggesting that this phenomenon is not as prevalent as observed in agricultural soils. If enhanced degradation was occurring, the additional applied chemicals would translate to added expenses or reduced profits due to decreased seedling yields. This research is vital for the managers of forest nurseries.
Technical Abstract: Recent studies have observed enhanced degradation of methyl isothiocyanate (MITC) from repeated fumigation in agricultural soils. Little is known about fumigant degradation in forest and nursery soils. This study was conducted to determine degradation rates of MITC and chloropicrin (CP) in two forest soils and the impacts of nursery management on degradation of MITC and CP. The half-life values of MITC and CP were evaluated in the laboratory under isothermal conditions (22±2°C). Three rates representing 0.5x, 1x, and 2x field application rates for each fumigant were used in laboratory incubations. Effect of microbial degradation was determined by conducting incubations with both fresh and sterilized soils. Soil moisture effects were also studied. There was no difference in MITC or CP degradation between fumigated and non-fumigated forest nursery soils. Soil sterilization and high soil moisture content (15% by wt.) reduced MITC and CP degradation. The degradation rates of MITC and CP varied with factors such as nursery history, fumigant application rates, and freshness of tested soils.