Influence of pyrolysis temperature on rice straw biochar properties and corresponding effects on dynamic changes in bispyribac-sodium adsorption and leaching behavior in soil

Bispyribac-sodium is a weakly acidic herbicide with high water solubility and is thus a potential source of groundwater contamination. Considering the risk inherent to the use of this herbicide, this study assessed the impacts of rice straw (RS) and biochar amendments on the adsorption and leaching behavior of bispyribac-sodium in soil. Biochars were produced from RS at different pyrolysis temperatures and characterized using various spectral techniques. Rice straw had a surface area of 3.996 × 104 m2 kg–1, which increased under pyrolysis; biochars prepared at 350 and 550 °C (RS350 and RS550) in a closed furnace with limited oxygen supply had a surface area of 5.763 × 104 and 6.890 × 104 m2 kg–1, respectively, and biochar prepared by purging the pyroformer with N2 (RSC) had the highest surface area of 12.173 × 104 m2 kg–1. After amendment with RS and biochar, soil Freundlich adsorption capacity (KFads) increased to varying extents in the order RSC > RS350 > RS550, from 2.89 × 103 to 29.57 × 103 mg1 – 1/n kg–1 L1/n, compared to 1.55 × 103 mg1 – 1/n kg–1 L1/n in unamended soil. The variability in KFads of bispyribac-sodium amongst the RS- and biochar-amended soils was dependent on the surface area of the amendments. The desorption of bispyribac-sodium decreased in the RS- and biochar-amended soils and varied from 90.45% to 95.20% in unamended soils and from 60.95% to 89.50% in amended soils. The adsorption and desorption of bispyribac-sodium varied significantly depending on its concentration and the type and application rate of soil amendment. Different leaching risk evaluation indices, viz., modified leach index (M.LEACH), leach index (LEACH), groundwater ubiquity score (GUS), Hornsby index (HI), leaching index (LIN), and pesticide leaching potential (PLP) index, were used to assess the susceptibility of groundwater to herbicide leaching. To reduce the repetitive effects of common parameters in each index, a new index was developed by employing principal component analysis (PCA) to condense their information into a single ranking. The results of the PCA indicated that RS and biochar amendments could be an effective management practice for controlling the leaching potential of bispyribac-sodium in soil.