De-oiled two-phase olive mill waste may reduce water contamination by metribuzin

The impact of de-oiled two-phase olive mill waste (DW) on the behavior of metribuzin in Mediterranean agricultural soils is evaluated, and the effects of the transformation of organic matter from this waste under field conditions are assessed. Four soils were selected and amended in the laboratory with DW at the rates of 2.5% and 5%. One of these soils was also amended in the field with 27 and 54 Mg ha(-1) of DW for 9 years. Significant increases in metribuzin sorption were observed in all the amended soils. In the laboratory, the 5% DW application rate increased the t1/2 values of metribuzin from 22.9, 35.8, 29.1, and 20.0 d for the original soils to 59.2, 51.1, 45.7, and 29.4d, respectively. This was attributable mainly to the inhibitory effect of the amendment on microbial activity. However, the addition of DW transformed naturally under field conditions decreased the persistence down to 3.93 d at the greater application rate. Both amendments (fresh and field-aged DW) significantly reduced the amount of metribuzin leached. This study showed that DW amendment may be an effective and sustainable management practice for controlling groundwater contamination by metribuzin.