The effect of liquid cow manure (LCM) on dimethenamid persistence was studied using amended soils with various stabilization times and LCM doses corresponding to specific field applications. Soils were amended with LCM doses equivalent to 100,000, 200,000, and 300,000 L ha-1. Dimethenamid (2-chloro-N-(2, 4-dimethyl-3-thienyl]-N-[2-methoxy-1-methylethyl) acetamide) was applied in a field dose. The study was conducted under controlled conditions using an Andisol without the prior application of the herbicide and LCM. Respiratory activity, fluorescein diacetate (FDA) activity, and residual dimethenamid were measured within a specific time period. The respiratory activity and FDA studies showed that LCM-amended soils were stabilized after 20 days in incubation and displayed no significant differences after applying dimethenamid. The half-life (t1/2) of dimethenamid in soil was 28 days; however, in LCM-amended soils, the half-life ranged from 13 to 21 days. In the amended soil, the t1/2 decreased significantly to 13 days in soils that contained the highest levels of LCM at 10 days of pre-incubation. The results show that both the dose and stabilization time of LCM-amended soils change the half-life of dimethenamid. Larger LCM doses are not recommended for field application. Dimethema-nid should be applied 20 days after the soil amendment to increase dimethenamid efficacy.