Influence of pyrolysis temperature on rice straw biochar properties and their effect on dynamic changes in bispyribac-sodium adsorption and leaching behaviour

Bispyribac sodium is a weakly acidic herbicide with high water solubility which causes a risk of groundwater contamination. Considering this, the impact of rice straw (RS) and biochar amendments was assessed on the fate of bispyribac sodium. Rice straw biochars were prepared at different pyrolysis temperature and characterized using various spectral techniques. RS has surface area of 39.96 × 10³ m² kg⁻¹ which increase on pyrolysis. Biochar prepared at 350 and 550 °C under oxygen limited conditions (RS350 and RS550) has surface area of 57.63 × 10³ and 68.90 × 10³ m² kg⁻¹ whereas biochar prepared under nitrogen conditions (RSC) has highest surface area of 121.73 × 10³ m² kg⁻¹. The adsorption capacity (KFₐdₛ) increased on amendment of soil with RS and biochars and varied from 1.55 × 10³ to 29.57 × 10³ mg¹⁻¹/ⁿ kg⁻¹ L¹/ⁿ in amended soils as compared to 1.55 × 10³ mg¹⁻¹/ⁿ kg⁻¹ L¹/ⁿ in unamended soil. The variability in the KFₐdₛ of bispyribac-sodium amongst RS and its biochar amended soils was in line with surface area of the amendments. Desorption of bispyribac-sodium decreased in RS and biochar amended soils and varied from 90.45 to 95.20 and 60.95 to 89.50% in unamended and amended soils. Adsorption and desorption of bispyribac-sodium varied significantly with the herbicide concentration and type and application rate of amendment in soil. Different indices viz. M. LEACH, LEACH, GUS, HI, LIN, PLP INDEX were used to assess the vulnerability 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) which condenses information into a single ranking. PCA suggested that RS and biochar amendment in soil might be an effective management practice in controlling leaching potential of bispyribac sodium.