The straw presence preceding soybean crop increases the persistence of residual herbicides

: Background: There is little information on how different soil cover systems influence the residual effect of pre-emergent herbicides used in soybean cultivation in Brazil. Objective: The objective was to compare the persistence of different pre-emergent herbicides in a Latosolic Dystrophic Red Nitosol soil in the presence or absence of black oat straw on the soil surface. Methods: The herbicides used were chlorimuron-ethyl (40.0 g ai ha -1 ), diclosulam (70.1 g ai ha -1 ), flumioxazin (100.0 ai g ha -1 ) and saflufenacil (70.0 g ai ha -1 ). Soil samples were collected at 0, 5, 10, 15, 20, 32, 46 and 60 days after herbicide application. The bioavailability of the herbicides was evaluated in a greenhouse using cucumber plants as bioindicators. Results: Rainfall was necessary for the herbicides to go through the straw layer and reach the soil. Using straw, the half-life times for chlorimuron, diclosulam, flumioxazin and saflufenacil were 42, 61, 49 and 26 days, while without straw, they were 23, 45, 8 and 10 days, respectively. Conclusion: The presence of straw on the soil surface increased the persistence of herbicides in the soil.