Cumulative and residual effects of de-oiled two-phase olive mill waste application to soil on diuron sorption, leaching, degradation, and persistence

Laboratory and field experiments were conducted to evaluate the influence of de-oiled two-phase olive mill waste (DTPOMW) amendments on the sorption–desorption, degradation, leaching, and persistence of the herbicide diuron in a representative olive grove soil. The soil was amended in the laboratory with DTPOMW at the rates of 5% and 10% (w/w), and in the field with 27 and 54 Mg ha−1 of DTPOMW for 7 years. Cumulative and residual effects were evaluated in the last year and 2 years after the last DTPOMW field application (2005 and 2007, respectively). The results showed that the adsorption of diuron to the soil significantly increased in the presence of DTPOMW in the laboratory and field-amended soils, and that humic acid content was mainly responsible for this increase. The DTPOMW soil application only significantly increased the half-life of diuron in the laboratory-amended soils, ranging from 8.6 d for the original soil to 51 d at the greater application rate. The DTPOMW amendments significantly reduced the downward mobility of diuron, and reduced the amount of herbicide leached in the laboratory and field-amended soils, and no residues of diuron were detected in the leacheate of the residual-amended columns. In the field study, DTPOMW addition increased the persistence of diuron in the upper 10 and 5 cm of the soils in the cumulative and residual years, respectively, decreasing the herbicide’s vertical movement through the amended soils with increasing DTPOMW rate. This study has shown that in olive grove soils DTPOMW amendment may be an effective management practice for controlling ground water contamination by diuron.