A study of herbicide carryover and soil interaction using in-field bioassay and nonequilibrium thin-disc methods

Research was conducted to evaluate herbicide carryover and herbicide-soil interactions. The first objective was to explore rotational crop injury from pyrithiobac carryover. Imazaquin was included as a reference standard. The second objective was to determine the influence of incubation time on desorption of imazaquin from field-moist soil in a thin-disc flow system and elucidate the most appropriate kinetics model to describe imazaquin leaching from a surface applications. The third objective was to use a novel method, dual-label thin-disc flow, to determine atrazine and imazaquin sorption to soil and compare the results those with a traditional batch method. The final object was to use the dual-label thin-disc method to measure the rapid-phase sorption kinetics of atrazine and imazaquin and compare the results to those from a traditional batch method.; Grain sorghum was most sensitive to carryover from 690 g ai ha −1 pyrithiobac applied the previous year followed by corn and then soybean. Cotton was the most sensitive crop to 690 g ai ha −1 imazaquin followed by com and then grain sorghum. Carryover treatments injured all rotational crops. The approximated half-life of pyrithiobac and imazaquin was 61 and 71 d, respectively. Layby applications of pyrithiobac were determined to have a higher than acceptable potential to injure com and reduce yield when grown after pyrithiobac.; Imazaquin sorption increased with time beyond 24-h incubation. Imazaquin desorption was kinetically driven in the initial stage but equilibrium limited as desorption continued. Diffusion-driven sorption processes with incubation times beyond 24 h more tightly sorbed imazaquin than rapid sorption processes.; Imazaquin and atrazine sorption was biphasic, with a much higher proportion of rapid sorption with atrazine than imazaquin. Imazaquin and atrazine 24-h K_f values equaled 0.35 and 2.41, respectively. Atrazine K _d determined with the dual-label thin-disc method was 1.54, compared to 1.38 with 5.0-min batch experiments. Imazaquin was too weakly sorbed to accurately determine a thin-disc flow K_d. The 5.0-min imazaquin K_f was 0.056 with the batch method. Elovich kinetics best described gradual phase herbicide sorption and desorption. Rapid-phase sorption kinetics determined by thin-disc flow agreed closely with those obtained with traditional batch methods.