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Spatial Variation in 2‐Methyl‐4‐chlorophenoxyacetic Acid Mineralization and Sorption in a Sandy Soil at Field Level
Author(s) -
Fredslund L.,
Vinther F. P.,
Brinch U. C.,
Elsgaard L.,
Rosenberg P.,
Jacobsen C. S.
Publication year - 2008
Publication title -
journal of environmental quality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.888
H-Index - 171
eISSN - 1537-2537
pISSN - 0047-2425
DOI - 10.2134/jeq2006.0208
Subject(s) - mcpa , mineralization (soil science) , sorption , environmental chemistry , chemistry , soil carbon , soil horizon , total organic carbon , subsoil , soil water , soil science , agronomy , environmental science , biology , pesticide , organic chemistry , adsorption
The phenoxyacetic acid herbicide MCPA (2‐methyl‐4‐chlorophenoxyacetic acid) is frequently detected in groundwater beneath Danish agricultural fields. We investigated spatial variation in microbial MCPA mineralization potential in a flat agricultural field of fine sandy soil (USDA classification: Humic Dystrudept) located on the Yoldia plains of Northern Jutland, Denmark. Samples for determination of MCPA mineralization and sorption were collected from the Ap and Bs horizons at 51 sampling sites located in a 200 × 220 m grid. Spatial variation in sorption was low in both horizons (distribution coefficient, 0.36–4.16 L kg −1 ). Sorption correlated strongly with soil organic carbon content in both horizons (CV, 93 and 83%, respectively) and negatively with soil pH. [Ring‐ 14 C]‐MCPA mineralized readily in the Ap horizon, with 49 to 62% of the 14 C‐MCPA being converted to 14 CO 2 during the 67‐d incubation period. With the subsoil, mineralization of 14 C‐MCPA varied considerably between samples (0.5–72.8%). At neither depth was there correlation between 14 C‐MCPA mineralization and sorption, soil pH, organic carbon content, clay content, number of colony‐forming units (CFU), pseudomonad CFU, or any of the four microbial activity parameters measured. The presence of microbial genes encoding for the TfdA enzyme was quantified using real‐time polymerase chain reaction. No correlation was found between MCPA mineralization potential and the natural background number of tfdA genes present in the soil samples. The degradation kinetics suggests that the high 14 C‐MCPA mineralization rate detected in soil samples was linked to growth of the MCPA‐degrading soil microbial community.