Sugarcane and pinewood biochar effects on activity and aerobic soil dissipation of metribuzin and pendimethalin

Biochars were produced by pyrolysis of sugarcane bagasse (350 °C and 700 °C) and pine wood (400 °C) and are abbreviated BC350, BC700, and WC400, respectively. Metribuzin adsorption by batch equilibrium showed that BC700 had the greatest adsorption capacity followed by BC350 and WC400. The bagasse biochars were mixed with clay and a silt loam soil and the pine wood biochar with a loamy sand soil and fortified with the metribuzin and pendimethalin. The soils were incubated at 25 °C in the dark and were extracted with methanol after 0, 7, 14, 21, 28, 42, 63, 86, and 111 days. Parent compounds and metribuzin degradates were analyzed in extracts by HPLC - mass spectrometry. Increases in metribuzin half life (DT50) were indicated for all soil-biochar combinations. BC350 had the greatest impact, doubling the DT50 in the silt loam soil. In contrast, BC700 had minimal impact on the DT50 in the silt loam soil and contributed to a significant DT50 decrease in the clay. The metribuzin degradate, metribuzin-desamino, was detected at rates proportional to metribuzin dissipation. For pendimethalin, biochar additions increased DT50 in all soil-biochar combinations. In contrast to metribuzin, BC700 and WC400 had the greatest impact with the BC700 increasing the DT50 more than 2-fold. In the loamy sand soil, the 1-4% biochar rate contributed to an increased trend in palmer amaranth emergence. At the 8% rate, palmer amaranth emergence was statistically higher than the control (p = 0.072). In sum, how biochar impacted the activity and dissipation of these herbicides depended on soil, herbicide, and biochar properties.