Leaching behaviour appraisal of eight persistent herbicides on a loam soil amended with different composted organic wastes using screening indices

The addition of organic wastes is a common agronomic practice in some Mediterranean regions to increase soil organic matter. In addition, they consume high amounts of agrochemicals. Hand-packed soil columns were used to evaluate the effect of three different composted organic soil amendments (agro-forestry, agro-industrial and animal manure) on the leachability of eight persistent herbicides. A new leaching index based on the amounts recovered from leachates and referred as Experimental Leaching Index (ELI) is proposed according to the mean annual precipitation in a specific place. This index is compared with others such as Groundwater Ubiquity Score (GUS), Relative Leaching Potential Index (RLPI) and Leachability Index (LIX), which only include degradation (DT50) and sorption (K-OC) parameters. According to ELI, metribuzin is very mobile in all cases, while terbuthylazine, chlorotolumn and isoproturon present high leachability only in unamended soil reducing their leaching potential in amended soils. Aclonifen, oxyfluorfen, trifluralin and pendimethalin behave in all cases as immobile (non-leacher) compounds.