Biochars mediated degradation, leaching and bioavailability of pyrazosulfuron-ethyl in a sandy loam soil

Burning of crop residues after harvest is a quick, cheap and an easy way to manage the large quantities of agricultural biomass for timely preparation of the field for next crop. Conversion of the crop harvest residues into biochars and incorporating them back in the same field can address the issue of land clearing, waste utilization and nutrient conservation but, any amendment to the soil changes its physico-chemical characteristics and can affect the fate of soil applied herbicides. The present study reports the effect of low (400 °C) and high (600 °C) temperature wheat (WBC) and rice (RBC) straw biochar's amendment on leaching, degradation and bioavailability of pyrazosulfuron-ethyl (PYRAZO) in a sandy loam soil. The PYRAZO was poorly retained in the control soil column where 78% of the soil-applied herbicide leached out of the control soil column. Biochars addition (0.02 and 0.05 g kg⁻¹) significantly reduced the PYRAZO leaching by affecting herbicide's breakthrough time and its maximum concentration in leachate.The biochars reduced PYRAZO degradation, both in the flooded and the nonflooded soils; but, effect was more pronounced in the nonflooded soils. The effect of biochars on PYRAZO's leaching and degradation was the function of the nature of feedstock, biochar production temperature and its dose. The high temperature biochars were more effective in reducing the leaching and degradation of PYRAZO than the low temperature biochars and the rice biochars were better than the wheat biochars. The bioavailability of PYRAZO was assayed by its effect on mustard seedlings and results suggested that low temperature biochars, even at 0.05 g kg⁻¹ level, had no negative effect on herbicide efficacy. However, high temperature biochars significantly reduced the herbicide bioavailability and higher concentration of PYRAZO was required for the desired effect. These findings are relevant in assaying the fate of PYRAZO in the biochar amended soils.