1791 Controlled land spreading of untreated olive mill wastewater (OMW) has been widely practiced as a means of its disposal. However, potential phytotoxic efects are critical for the selection of sites and crop types and for proper synchronization between land application and cropping. Tis study traced the fate of dissolved organic carbon (DOC), total phenols (TP), electrical conductivity, pH, microbial counts, and phytotoxicity to cress (Lepidium sativum L.) afer soil application at doses equivalent to 80, 160, and 320 m 3 ha -1 . Vertisol (fne-clayey) and Loess (sandy loam) soils were treated and incubated at 12 or 25°C and at moisture contents maintained at 70% of feld water capacity or gradually reduced from 70 to 20% without compensation. Temperature, rather than moisture content, had a major efect on removal rates of DOC and TP. Te maximum combined efect of warm temperature and higher moisture content resulted in removal rates greater than those under cooler, drier conditions by factors of up to 1.8 and 4.1 for DOC and TP, respectively. Favorable biodegradation conditions were indicated by increased numbers of total soil microorganisms and fungi by factors of up to 26 and 5, respectively. A whole-soil bioassay was developed to assess the dynamics of residual soil phytotoxicity afer OMW application. Phytotoxicity measurement in soil extract generally showed stronger inhibition or stimulation activity than measurement in whole soil, depending on soil type and OMW dose. Te newly developed bioassay seems to be useful for the refnement of general recommendations regarding permitted OMW application doses. Fate of Soil-Applied Olive Mill Wastewater and Potential Phytotoxicity Assessed by Two Bioassay Methods Ibrahim Saadi, Michael Raviv, Shimrit Berkovich, Aviva Hanan, Ido Aviani, and Yael Laor* T he olive oil industry is a major agro-industrial sector in Mediterranean countries. However, olive oil–produc- ing countries face serious ecological problems because of a lack of applicable economical means for disposing of the olive mill wastewater (OMW) generated by this industry. Te extremely high organic load and the toxic nature of OMW pre- vent their direct discharge into domestic wastewater treatment systems (Rozzi and Malpei, 1996; Sayadi et al., 2000; Di Gioia et al., 2002). One alternative economical solution is controlled land spreading; in fact, Italian law already permits spreading up to 50 or 80 m 3 ha -1 yr -1 for OMW generated by press or con- tinuous centrifugation, respectively (Rinaldi et al., 2003). In this context, OMW is considered as a natural fertilizer that, at proper application rates, is not harmful to crops and can be spread with- out causing environmental damage (Altieri and Esposito, 2008). Raw OMW has been shown to be toxic to plants even at 100- fold dilution (Saadi et al., 2007; Hanif and El Hadrami, 2008; Aviani et al., 2009; Muscolo et al., 2010; Piotrowska et al., 2011); therefore, OMW application to agricultural land carrying orchards or feld crops is ofen seen as unfavorable. However, at safe application rates and with appropriate synchronization between application and cropping, OMW could be used as a natural herbicide (Erez-Reifen et al., 2009), favoring its use in organic and sustainable farming. Although the phytotoxicity of OMW is ofen attributed to its high phenolic content, nonphenolic organic compounds as well as inorganic salts and trace heavy metals likely contribute to its overall phytotoxicity (Kistner et al., 2004; Ben Sassi et al., 2006; Aviani et al., 2009, 2010). Tus, the contribution of OMW to soil phytotoxicity probably depends on specifc as well as synergistic contributions of its phytotoxic constituents. Afer land application, some studies showed only short-term phytotoxic efects lasting a few weeks (Piotrowska et al., 2006; Saadi et al., 2007), but Mekki et al. (2007) detected increased Abbreviations: DOC, dissolved organic carbon; EC, electrical conductivity; IRF, initial removal fraction; OMW, olive mill wastewater; TP, total phenols. I. Saadi, A. Hanan, and Y. Laor, Agricultural Research Organization, Institute of Soil, Water and Environmental Sciences, Newe Ya’ar Research Center, Ramat-Yishay, Israel; M. Raviv, Agricultural Research Organization, Institute of Plant Sciences, Newe Ya’ar Research Center, Ramat-Yishay, Israel; S. Berkovich, Agricultural Research Organization, Institute of Soil, Water and Environmental Sciences, Newe Ya’ar Research Center, Ramat-Yishay, Israel and Ort Braude College, Dep. of Biotechnology Engineering, Karmiel, Israel; I. Aviani, Agricultural Research Organization, Institute of Plant Sciences, Newe Ya’ar Research Center, Ramat- Yishay, Israel and Dep. of Microbiology and Plant Pathology, Faculty of Agriculture, Food and Environment, the Hebrew Univ. of Jerusalem, P.O. Box 12, Rehovot 76100, Israel. Assigned to Associate Editor Tiequan Zhang. Copyright © American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America. 5585 Guilford Rd., Madison, WI 53711 USA. All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. J. Environ. Qual. 42:1791–1801 (2013) doi:10.2134/jeq2012.0331 Received 30 Aug. 2012. *Corresponding author (laor@agri.gov.il). Journal of Environmental Quality PLANT AND ENVIRONMENT INTERACTIONS TECHNICAL REPORTS Published June 25, 2014