Effects of long-term irrigation with reclaimed wastewater on the efficacy and fate of trifloxysulfuron-sodium in the soil

Long-term irrigation with reclaimed wastewater (RWW) is known to affect the physical, chemical and biological properties of the receiving soil. The sulfonylurea herbicide trifloxysulfuron-sodium (TFX), an acetolactate synthase inhibitor, is stable in the soil for several months and can carry over to rotational crops; however, its activity in RWW-irrigated soils is much lower. In this study, we monitored the activity/dissipation of TFX applied on RWW-irrigated soil. High weed infestation in the treated soil in field studies along with a decrease in the soil activity as determined with test plant was observed, suggesting fast dissipation of the herbicidal activity of TFX in the soil. Dose-response curves of Sorghum bicolor to TFX planted in RWW- and in fresh water-irrigated soils showed higher and more significant damage for both shoots and roots with the fresh water-irrigated soil. Sterilised RWW-irrigated soil exhibited higher TFX activity versus non-sterilised soil. This implies that reduction in TFX activity in RWW-irrigated soil is probably affected by the microbial activity.