Effect of olive-mill waste addition to soil on sorption, persistence, and mobility of herbicides used in Mediterranean olive groves

Laboratory and field experiments were conducted to evaluate the effect of olive-mill waste (OMW) addition to a Mediterranean olive grove soil on sorption, persistence, and mobility of two herbicides which are simultaneously applied for weed control in olive groves: terbuthylazine (TA) and fluometuron (FM). Laboratory batch sorption experiments showed that OMW addition to the soil at rates of 5 and 10% (w/w) greatly enhanced the sorption of both herbicides, thus suggesting that amendment with OMW could be useful to enhance the retention and reduce the mobility of FM and TA in the soil. Incubation experiments showed that OMW increased the persistence of FM and had little effect on the long persistence of TA in the soil studied. A demonstration field experiment was also conducted in field plots with a slope of about 5%, either unamended or amended with OMW at a rate of 10 kg m⁻², and then treated with a commercial formulation containing a mixture of TA and FM. Extraction of field soil samples, taken from different soil depths (0-5, 5-10, 10-20, and 20-30 cm) at different times after herbicide application, showed that both TA and FM moved deeper in unamended soil than in OMW-amended soil, and that OMW addition affected the persistence of FM in the toplayer, increasing its half-life from 24 to 58 days, while having little effect on the persistence of TA. Thus, data obtained under real field conditions were consistent with those obtained under controlled laboratory conditions. Preliminary herbicide runoff data indicated that the total herbicide runoff losses were also reduced upon OMW addition. Addition of OMW could be beneficial in reducing the mobility of TA and FM in olive grove soils, and also in increasing the persistence of FM in soils where this herbicide could be rapidly degraded.