Chlorotoluron mobility in compost amended soil

Knowledge about the impact that various organic amendments have on the behavior of pesticides in soils is essential when assessing groundwater contamination risk. The aim of this study was to evaluate the impact of a compost amendment on chlorotoluron mobility in the A horizon of the Luvic Chernozem. Soil was mixed with compost material and placed into plastic cylinders. Eight mixtures (A, B, C, D, E, F, G and H) of various compost fractions (from 1 to 8% of mixture weight) were prepared. Chlorotoluron solution was applied on the top of the soil samples and a rainfall simulator was used to apply distilled water on the soil surfaces with controlled infiltration rates. Measured pressure heads at 3 positions, water outflow from the bottom, and final chlorotoluron concentrations within the soil samples were used to optimize soil hydraulic and herbicide transport parameters via numerical optimization using the HYDRUS-1D code. Optimized soil hydraulic parameters did not show noticeable changes (demonstrating an improvement of soil hydro-physical properties) with increasing compost fraction. Final chlorotoluron distribution in soil columns and estimated transport parameters also showed high variability. However, results indicated that while chlorotoluron mobility decreased up to a compost fraction of 6%, herbicide mobility noticeably increased in G (7%) samples and slightly increased in H (8%) samples. These finding corresponded to herbicide adsorption studied using a batch experiment. Multiple linear regressions revealed that other properties (not only organic carbon content) play a noticeable role in pesticide adsorption in soils. A negative impact of pHKCl (which was positively affected by compost addition), clay content, and CaCO3 content (which were mostly properties of soil, but could be affected by compost composition as well) was documented.

► Properties of soil amended by 8 increasing organic compost fractions were studied.
► Transport of herbicide in soil columns was studied experimentally and mathematically.
► Increasing trend of Cox, pHKCl, CEC with increasing compost fraction was observed.
► Analysis did not show noticeable changes soil hydro-physical properties.
► Herbicide mobility depended on Cox, pHKCl, clay and CaCO3 content.