TECHNICAL ARTICLESDEGRADATION KINETICS ASSESSMENT FOR THE FUNGICIDE BAS 505 IN INTACT SOIL CORES VERSUS BATCH SOILSMcDonald, Jason A.1; Gaston, Lewis A.1; Jackson, Scott H.2; Locke, Martin A.3; Zablotowicz, Robert M.4Author Information 1Department of Agronomy and Environmental Management, LSU AgCenter, Baton Rouge, LA. Dr. Jason A. McDonald is corresponding author. E-mail: [email protected] 2BASF Corporation, Research Triangle Park, NC. 3USDA-ARS-WQEP-NSL Research Station, Oxford, MS. 4USDA-ARS-SWSRU Research Station, Stoneville, MS. Received May 23, 2005; accepted Sept 13, 2005 Soil Science: March 2006 - Volume 171 - Issue 3 - p 239-248 doi: 10.1097/01.ss.0000187375.38649.5b Buy Metrics Abstract Field degradation rates of pesticides are often different than determined in the laboratory using homogeneous soil. This project developed an intact soil core method for determining aerobic degradation rate that is intended to address such discrepancies. The fungicide BAS 505 (phenyl-U-14C-labeled) [N-methyl-(E)-2-methoxyamino-2-(2-((2,5-dimethylphenoxy)methyl)phenyl)acetamide] was applied to surface 0-7.5 cm of Ruston (fine loamy, siliceous, thermic Typic Paleudults) soil cores (triplicate and duplicate series) and homogeneous (batch) soil in biometer flasks (triplicate). Recovery was measured 12 times over the 360-day incubation. Mineralization rate in cores was initially slower than in batch soil but increased to give more 14CO2 lost by Day 360 (11% and 8% of applied, respectively). Unextractable 14C was 21% in cores, similar to that for batch soil (18%). Recovery of BAS 505 in combined MeOH and MeOH-water extracts (HPLC-LSC analysis) after 360 days averaged 36% from cores and 57% from batch soil. Degradation rate in both systems decreased over time and could be described by Nth order kinetics but not first order. Recoveries of BAS 505 by 360 days were lower in cores, indicating faster degradation than in batch soil after long-term incubation. Lack of nutrient inputs may account for decreasing degradation rates; however, decreasing microbial activity with time was not shown by the highly variable biomass C data. Faster degradation in cores may have been due to higher microbial populations/nutrient levels in the surface soil. © 2006 Lippincott Williams & Wilkins, Inc.