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 8.6d 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.

Changes in organic matter and residual effect of amendment with two-phase olive-mill waste on degraded agricultural soils.

Agricultural soils from many parts of the Mediterranean region are very poor in organic matter and are exposed to progressive degradation processes. Therefore, additions of the olive-mill waste from a continuous two-phase system as an organic amendment can improve soil quality and hence mitigate the negative environmental and agronomic limitations of these soils. A field study under semiarid Mediterranean conditions was conducted to evaluate the changes in organic matter after four consecutive annual additions of olive-mill watery husk (OMWH) waste and the de-oiled two-phase olive pomace (TPOP) waste on an olive grove soil: a cutanic Luvisol (CL). Treatments included a control, OMWH (30 and 60 Mg ha(-1), DW equivalent), and TPOP (27 and 54 Mg ha(-1), DW equivalent). Also, a two-year greenhouse study using wheat (Triticum aestivum L.) was conducted to evaluate the residual effects of adding OMWH to CL soil and to a degraded Leptic Cambisol (LC). Treatments included five OMWH rates ranging from 0 to 40 Mg ha(-1). Significant increases in total organic carbon (TOC), water soluble organic carbon (WSOC), humic and fulvic acids, and aggregate stability were observed in the treated plots, and the highest humification index was obtained when OMWH was applied at the lowest rate. The increase in aggregate stability correlated positively and highly significantly (P<0.01) with the humic and fulvic acid and WSOC contents. In the greenhouse, significant increases in TOC, carbohydrates, aggregate stability, total N, available K, and cation exchange capacity were observed in both soils. However, available P decreased significantly. There was an increased residual fertilization effect of OMWH for both soils. The best fits to grain yield and OMWH rates were with a linear regression for the CL soil (R(2)=0.957 and P<0.01), and a quadratic regression for the LC soil (R(2)=0.960 and P<0.01).