Downloaded by PENNSYLVANIA STATE UNIV on September 3, 2012 | http://pubs.acs.org Publication Date: March 1, 2002 | doi: 10.1021/bk-2002-0813.ch014
Chapter 14
Changes in Soil Biomass and Microbial Community Structure as Affected by Storage Temperature and Duration: Effect on the Degradation of Metsulfuron Methyl 1,2
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Steven L. Trabue , Tara M. Crowe , and Joseph H. Massey 1
DuPont Crop Protection, P.O. Box 80402, Newark,DE19714 Current address: DuPont Agricultural Products, Stine-Haskell Research Center, DuPont, 1090 Elkton Road, Newark,DE19714-0030 Current address: Department of Plant and Soil Sciences, Mississippi State University, Starksville, MS 39762
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The persistence of crop protection products (CPP) in field studies is often less than that observed i n laboratory studies conducted on the same soils. In this study, the effects of prior soil storage on microbial biomass and community structure were measured in conjunction with the disappearance and mineralization of [phenyl (U)- C] metsulfuron methyl herbicide. Laboratory soils i n this study were collected and used fresh (stored less than 3 weeks) or stored at 4 and 20 °C for 3 and 6 months prior to use. The phospholipid fatty acid technique was used to monitor changes in the microbial biomass. Results indicate that both the storage duration and temperature significantly impacted the soil biomass, while the degradation and mineralization of metsulfuron methyl were only significantly impacted by the duration of storage. 14
© 2002 American Chemical Society In Pesticide Environmental Fate; Phelps, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2002.
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Introduction Currently, U S E P A regulatory guidelines require an aerobic soil metabolism study and at least two terrestrial field dissipation studies completed for the registration of crop protection products (CPP). Often the half-lives generated in the laboratory are generally longer than those generated in the field (1,2). The longer laboratory half-lives for some CPP may in part be attributed to a decline in the viability of the soil biomass during storage. This is especially true i f biotic degradation plays a significant role in the CPP degradation. Studies on the effect of storage to soil have reported declines in soil biomass (3,4,5), community structure (6,7), and genetic diversity (8) during storage. For CPP in which microorganisms are the predominate agent involved in their transformation, differences between the degradation rates in laboratory compared to field may ultimately be linked to changes that occur during a soil's storage. Thus a better understanding of how storage affects a soil's microbial community may improve the design and interpretation of laboratory soil metabolism studies of CPP. This laboratory study was designed to investigate the effect storage duration and storage temperature have on a soil's microbial community and, in turn, how these changes affect its capacity to degrade metsulfuron methyl. Metsulfuron methyl was chosen as the probe compound since it has a moderate half-life of 10-30 days (9,10), and has a large microbial component to its degradation (10). Abiotic degradation (hydrolysis) of metsulfuron methyl was minimized in this study through the use of an alkaline (pH 8.0) soil.
Materials and Methods
Soil Selected soil properties are listed in Table I. Soil samples were collected from a potato field in American Falls, Idaho, on October 8, 1998 and sieved through a 2-mm sieve prior to storage. Soils were stored in the dark at field moisture levels (57% of 1/3 bar). The storage conditions investigated in this study were the following: 1) fresh soil stored for
