Ffect of Olive mill wastewater spreading on soil under different climatic condition in a semi humid area: A field study in Bait Reema – West Bank – Palestine.

Abstract

Olive mill wastewater (OMW) is generated seasonally in large amounts during the olive oil production in Palestine and it is often discharged in the open environment. OMW has a high amount of phototoxic compounds, high salinity and acidity and therefore is challenging when disposed on soil. The objective of this study was to understand the effect of OMW disposal on soil, and to identify short-term and long-term effects associated to OMW application on soil water chemical interactions. In order to understand how climatic conditions at the time of OMW disposal affect the development of soil properties, we conducted a field study in Bait Reema village in the West Bank – Palestine. The study site is characterized by 1.5 m thick brown rendzina and has an annual average rainfall of 550 mm. On an extensively used olive orchard field, we implemented 16 plots (2.5 x 3.5 m). OMW application (14 L / m 2 ) was conducted either in winter, spring or summer on two replicate plots distributed randomly among the 16 plots. To test the effect of soil moisture on the persistence of OMW effects, we implemented an OMW application in summer on two additional plots, but kept those plots moist for 2 weeks before OMW application until start of the rain season. For each of the treatmant variants, we implemented two control plots which were treated in the same way as their counterparts, but with tap water. Soil samples at 0-5, 5-10, 10-15, 15-25 and 25-35 cm depth were collected after 2 days, 3 weeks, 6 weeks, 3 months, 6 months and 9 months. EC, pH, soluble cations and anions were determined and analyzed in aqueous soil extracts (1:5), the total phenol content was determined by using Folin–Ciocalteu’s reagent, and wettability in the field was determined via WDPT for control and treated plots. While all control plots remained wettable during the whole year, OMW lead induced water repellency in all treatments analysed by now. The extent of hydrophobization was strongest in the dry summer application plots, intermediate in the spring application plots and weakest in the moist summer application. The results of OMW application during spring showed increase in EC, Na, WDPT and total phenols with the highest concentrations found in the upper layer. pH was significantly reduced by OMW application. In addition, we found a secondary acidification also weeks after OMW application, which probably was due to microbial degradation of the N containing organic OMW constituents. Interestingly, most of those effects disappeared after the rain season except for the acidity in deeper layer and K addition. Latter may be due to additional specific K binding in clay minerals. In addition to these effects, seasonal changes of the parameters were observed especially during summer time.