Field appraisement of olive mills solid waste application in olive crops: Effect on herbicide retention

The aim of this work was to study the effect of soil application of a solid waste from olive oil production (alperujo) on diuron and terbuthylazine retention in the field. Laboratory sorption experiments of the herbicides in unamended soil and soil amended with alperujo (A) or composted alperujo (CA) were performed, and a field study was conducted for 2 consecutive years. Three subplots composed of four olive trees were randomly selected from a 50-ha olive grove (SE Spain) for three different treatments: soil without amendment (S plots), soil amended with uncomposted alperujo (S + A plots) and soil amended with composted alperujo (S + CA plots). Uncomposted alperujo was applied to S + A plots during 4 consecutive years at the rate of 18 Mg ha−1 and composted alperujo was applied to S + CA plots for the first time on April 2005 at the rate of 8 Mg ha−1. On April 2006, 15 Mg ha−1 of A was applied to S + A plots, and 13 Mg ha−1 of CA was applied to S + CA plots. Manual application of both A and CA was followed by soil tillage to a 5 cm depth. A commercial herbicide formulation (28.5% diuron and 28.5% terbuthylazine) was applied to S, S + A and S + CA subplots and soils were sampled periodically at 0–10, 10–20 and 20–30 cm depth and extracted for their herbicide content. Results from laboratory studies indicated higher herbicide sorption upon amendment with both A and CA when compared to unamended soil. Field studies revealed higher amounts of diuron and terbuthylazine in every plot and almost all sampling dates in the first 10 cm of soil. Soil amendment with alperujo gave rise to higher amounts of herbicide in the soil when compared to unamended soil, and this is specially significant in the case of the herbicide diuron and plots amended with uncomposted alperujo.