Study on Bioavailability of some Wheat Herbicides in Different Tillage Systems and their Impact on Corn

This experiment was conducted to study the residual effect of some wheat herbicides on following corn (Zea mays L.) crop under different tillage systems in Karaj province. Tillage treatments included: conventional tillage, minimum tillage and, no-tillage. Herbicide treatments were: 1- bromoxynil MCPA (EC 40%) 1.5 lit/ha, 2- triasulfuron dicamba (WG 70%) 150 gr/ha, 3- mesosulfuron-methyl iodosulfuron-methyl-sodium (62 WG) 400 gr/ha, 4- metsulfuron methyl sulfosulfuron (w/v %5) 36 gr/ha, 5- tribenuron methyl (EC 8%) clodinafop propargyl (DF 75%) 20 gr/ha and 0.8 lit/ha respectively, as well as unweeded control (without herbicide). Soil sampling for bioassay tests made from surface layer (0-12.5 cm) and, sub-surface layer (12.5-25 cm). Bioassay experiment was conducted with Cress (Lepidium sativum) as a test plant and corn. Cress emergence percentage and cress and corn dry matter and height was assessed. Results indicated that herbicide bio- availability was depended on tillage system; in fact herbicide bio-availability was minimum in no-tillage systems. Triasulfuron dicamba, mesosulfuron-methyl iodosulfuron-methyl-sodium and metsulfuron methyl sulfosulfuron were the most persistent herbicide based on bio-availability, respectively. Therefore, these herbicides may damage the following corn crop in rotation although, corn was more tolerant to metsulfuron methyl sulfosulfuron. On the other hand, the persistence of bromoxynil MCPA and tribenuron methyl clodinafop propargyl herbicides in the soil was negligible and damage seems unlikely by theses herbicide in rotation.