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

Abstract

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 m(2) areas were two to three times lower than the field-scale variation within the entire field of about 4 ha.

Prediction of the glyphosate sorption coefficient across two loamy agricultural fields

“…Neither was it possible for Singh et al (2014) to detect any correlations between the glyphosate sorption coefficient and pH, clay and sand and only weak correlations was obtained with soil organic carbon (r = −0.21, p b 0.001) and silt (r = − 0.11, p b 0.001). Furthermore, Vinther et al (2008) only showed a weak spatial correlation between the glyphosate sorption coefficient and clay (r = 0.36, p b 0.01) and OC (r = 0.38, p b 0.01).…”

Application of a glyphosate-based herbicide to Phragmites australis: Impact on groundwater and near-shore lake water at a beach on Georgian Bay

“…Glyphosate has been reported to degrade rapidly in soil above the water table because most of the microbial activity responsible for degradation of glyphosate occurs in the upper and surface horizon of the soil (Borggaard and Gimsing, 2008;Ermakova et al, 2008;Kjaer et al, 2005;Major et al, 2003;Simonsen et al, 2008;Veiga et al, 2001;Vinther et al, 2008). Degradation will contribute to the rapid decline in concentrations of glyphosate over time.…”

“…However, rainfall will increase leaching of glyphosate in all soil textures and increase concentrations of glyphosate at the water table (Borggaard and Gimsing, 2008;Stone and Wilson, 2006;Vereecken, 2005). Glyphosate undergoes rapid degradation to AMPA (aminomethylphosphonic acid) in soils due to microbial activity, with a degradation half-life of 7 to 100 days depending on the environmental conditions (Borggaard and Gimsing, 2008;Ermakova et al, 2008;Kjaer et al, 2005;Major et al, 2003;Simonsen et al, 2008;Vinther et al, 2008). The results of these studies, which were undertaken in agricultural and urban settings, may not be transferable to a beach environment.…”

Predictivity Strength of the Spatial Variability of Phenanthrene Sorption Across Two Sandy Loam Fields

“…Sorption coefficients for atrazine, isoproturon and metamitron have been found to spatially correlate with OC and clay content within a 135-ha catchment (Charnay et al 2005). Besides sorption, OC content has also been found to play a role in pesticide mineralization and microbial activity (Vinther et al 2008). Gaultier et al (2006) found that for the A horizon, regression models including only soil OC and carbonate content were sufficient to successfully predict 2,4-D sorption.…”