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TECHNICAL REPORTS

Ground Water Quality

Field-Scale Variation in Microbial Activity and Soil Properties in Relation to Mineralization and Sorption of Pesticides in a Sandy Soil

^a Univ. of Aarhus, Faculty of Agricultural Sciences, Inst. of Agroecology and Environment, DK-8830 Tjele, Denmark
^b Geological Survey of Denmark and Greenland, Dep. of Geochemistry, DK-1350 Copenhagen K, Denmark
^c Biotech Research and Innovation Centre (BRIC), Fruebjergvej 3, DK-2100 Copenhagen Ø, Denmark

^* Corresponding author (bo.v.iversen{at}agrsci.dk).

Received for publication May 22, 2006. Pesticides applied to agricultural soils are subject to environmental concerns because leaching to groundwater reservoirs and aquatic habitats may occur. Knowledge of field variation of pesticide-related parameters is required to evaluate the vulnerability of pesticide leaching. The mineralization and sorption of the pesticides glyphosate and metribuzin and the pesticide degradation product triazinamin in a field were measured and compared with the field-scale variation of geochemical and microbiological parameters. We focused on the soil parameters clay and organic carbon (C) content and on soil respiratory and enzymatic processes and microbial biomass. These parameters were measured in soil samples taken at two depths (Ap and Bs horizon) in 51 sampling points from a 4-ha agricultural fine sandy soil field. The results indicated that the spatial variation of the soil parameters, and in particular the content of organic C, had a major influence on the variability of the microbial parameters and on sorption and pesticide mineralization in the soil. For glyphosate, with a co-metabolic pathway for degradation, the mineralization was increased in soils with high microbial activity. The spatial variability, expressed as the CV, was about five times higher in the Bs horizon than in the Ap horizon, and the local-scale variation within 100 m² areas were two to three times lower than the field-scale variation within the entire field of about 4 ha.

Abbreviations: ASA, arylsulfatase activity • CFU, colony-forming units • FDA, fluorescein diacetate • ISR, in situ soil respiration • Np, nitrophenol • SIR, substrate-induced respiration