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Rate of bentazone transformation in four layers of a humic sandy soil profile with fluctuating water table
Author(s) -
Leistra Minze,
Smelt Johan H,
Matser Arriënne M,
Bogte Jaap J,
van der Pas Leo J T
Publication year - 2001
Publication title -
pest management science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.296
H-Index - 125
eISSN - 1526-4998
pISSN - 1526-498X
DOI - 10.1002/ps.384
Subject(s) - subsoil , soil science , water table , aquifer , groundwater , vadose zone , environmental chemistry , soil horizon , soil water , environmental science , brackish water , topsoil , phreatic , chemistry , geology , salinity , oceanography , geotechnical engineering
The rate of transformation of a pesticide as a function of the depth in the soil is needed as an input into computations on the risk of residues leaching to groundwater. The herbicide bentazone was incubated at 15 °C in soil materials derived from four layers at depths of up to 2.5 m in a humic sandy soil profile with a fluctuating water table (0.8 to 1.4 m), while simulating the redox conditions existing in the field. Gamma‐irradiation experiments indicated that bentazone is mainly transformed by microbial activity in the soil. The rate constant for transformation was highest in the humic sandy top layer; it decreased with depth in the sandy vadose subsoil. However, material from the top of the phreatic aquifer had a higher rate constant than that from the layers just above. The presence of fossil organic material in the fluviatile water‐saturated sediment probably stimulated microbial activity and bentazone transformation. The changes in the transformation rate constant with depth showed the same trend as those in some soil factors, viz organic carbon content, water‐extractable phosphorus and microbial density as measured by fluorescence counts. However, the (low) concentration of dissolved organic carbon (DOC) in the top of the aquifer did not fit the trend. The rate constant for bentazone transformation in the layers was higher at lower initial contents of the herbicide. © 2001 Society of Chemical Industry