Propisochlor retention and mobility in the presence of straw in Brazilian cropping systems

Non-ionic herbicides, such as propisochlor, are more easily retained in organic soil fractions. The presence of straw in tropical cropping systems can affect herbicide transposition to the underlying seed banks and their environmental behavior. The aim of this study was to evaluate propisochlor soil retention in the presence of soybean and sugarcane straw (0, 5 and 10 t ha(-1)) through radiometric techniques. Most of the applied C-14-propisochlor was retained in the soil profile (18.2-39.4%) following an extreme rainfall simulation in the presence of straw. Decreased herbicide leaching was observed in the presence of sugarcane and soybean straw (0.7-0.5%), compared with soil without straw (1.8%). Hysteresis values ranged from 0.8 to 1.0, indicating that propisochlor sorption was reversible allowing for soil seed bank effects, as well as environmental dissipation. These findings indicate that propisochlor can overcome straw barriers, although representing low groundwater contamination risks. Because of this, reduced environmental impacts following the application of this herbicide are noted for tropical cropping systems containing straw mulch.