Abstract

This work studied the sorption and mobility of dimethenamid (2-chloro-N-(2,4-dimethyl-3-thienyl)-N-(2-methoxy-1-methylethyl)-acetamide) in soil amended with liquid cow manure (LCM) at doses equivalent to 0, 100, 200 and 300 thousand L ha-1 (D0, D100, D200 and D300 respectively). For the batch sorption study the amended soils were previously incubated for 30 days under controlled conditions. The mobility was evaluated under field conditions, determining the herbicide retained in different soil profiles and its concentration in soil solutions sampled with ceramic suction cups. Application of LCM at the two lowest doses (D100 and D200) did not modify dimethenamid adsorption, however adsorption increased at D300 (Kfoc = 62.1) as compared with D0 (Kfoc = 42.3). This result could be explained by the higher content of dissolved organic matter in D300, since the addition of LCM does not change the organic matter content in the soil. The results of the field trials showed that D300 adsorbed the highest amount of dimethenamid in the upper layer of soil, and that the amount of dimethenamid in leachates was lower than that of D0. The results showed that high doses of amendment contribute to higher herbicide retention in the topsoil, reducing leaching.