We investigated the effect of untreated and biologically treated olive mill wastewater (OMW) spreading on the soil characteristics and the microbial. communities. The water holding capacity, the salinity and the content of total organic carbon, humus, total nitrogen, phosphate and potassium increased when the spread amounts of the treated or untreated OMW increased. The OMW treated soil exhibited significantly higher respiration compared to the control soil. However, the C-CO2/C-tot ratio decreased from 1.7 in the control soil. to 0.5 in the soil. amended with 100 m(3) ha(-1) of untreated OMW. However, it slightly decreased to 1.15 in the soil. amended with 400 m(3) ha(-1) of treated OMW. The treated OMW increased the total mesophylic number while the number of fungi and nitrifiers decreased. Actinomycetes and spore-forming bacteria were neither sensitive to treated nor to untreated OMW. The total coliforms increased with higher doses of treated and untreated OMW. A toxic effect of the untreated OMW appeared from 100 m(3) ha(-1). This toxicity was more significant with 200 m(3) ha(-1), where microflora of total mesophilic, yeasts and moulds, actinomycetes, and nitrifiers were seriously inhibited except for total. coliforms and spore-forming bacteria. (C) 2005 Elsevier GmbH. All rights reserved.
