Submitted to: Soil Science Society of America Journal
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/15/2005
Publication Date: 11/15/2005
Citation: Stromberger, M.E., Klose, S., Ajwa, H.A., Trout, T.J. 2005. Microbial Populations and Enzyme Activities in Soils fumigated with Methyl Bromide Alternatives. Soil Science Society of America Journal, 2005, Vol 69: 1987-1999. Interpretive Summary: Methyl bromide, a commonly used soil fumigant, is being phased out because it depletes stratospheric ozone. Several alternative fumigants are being tested as alternatives to methyl bromide, including Telone (1,3-dichloropropene), chloropicrin, iodomethane, and propargyl bromide. Fumigants, although general biocides, do not kill all microbial life, but strongly impact the soil microbial community. It is important to know how fumigants impact the populations of the various types of bacteria and fungi. A field trial, carried out in strawberry growing areas of California where fumigants are commonly use, studied the die back and re-colonization of several classes of soil fungi and bacteria following fumigation with the various fumigants. As was expected, the fumigants affected the soil microbial communities in varying ways. The impacts of fumigants on microbial populations are complex and more study is required to understand the implications of fumigant use on the soil biology and plant response.
Technical Abstract: Except for approved critical uses, methyl bromide (MeBr) use for soil fumigation will be banned in 2005 due to its ozone depleting properties. Potential alternative chemicals to replace methyl bromide include chloropicrin (CP), 1,3-dichloropropene (1,3-D), iodomethane (IM), and propargyl bromide (PrBr). The goal of this research was to assess changes in soil fungal populations, microbial biomass C, respiration, nitrification potential, and enzyme activities after fumigation with MeBr and alternative fumigants. Four formulations of fumigants [CP, InLine™ (61% 1,3-D plus 33% CP), Midas™ (50% IM plus 50% CP), and PrBr] were drip-applied at commercial rates through drip irrigation systems to two field plots located in main strawberry production areas in California, USA. Soil samples (0-15 cm) were taken at 1, 4, and 30 or 37 weeks after fumigant application. MeBr and the alternative fumigants reduced culturable fungal populations and eliminated soil-borne fungal pathogens in soil. Microbial respiration decreased 45 to 80%?) with fumigant application and was the least in the PrBr treatment. Soil microbial biomass C was not affected by fumigation, indicating minor microflora activity. The activity of acid phosphatase and arylsulfatase was generally lower in fumigated soils over the 7 to 9 month study period, and those of b-glucosidase and dehydrogenase up to 4 weeks past fumigation. Potential nitrification rates were substantially reduced (>55%) by fumigation, but rates recovered towards the end of this study. Results of this study suggested that fungal populations and acid phosphatase and arylsulfatase activities were more sensitive to fumigation with the tested MeBr alternatives than total microbial biomass, microbial respiration, dehydrogenases and b-glycosidase activities, and nitrification.