Changes in soil chemical and biochemical properties following amendment with crude and dephenolized olive mill waste water (OMW)

Olive Mill Wastewater (OMW), a C-rich organic waste with high contents of both toxic phenols and valuable nutrients, is yearly produced in large amounts in the Mediterranean area. A possible recycling option is to spread it on agricultural land, provided that phytotoxic effects are neutralized. Research studies were performed on the use of OMW for soil fertigation in a laboratory model system. It consisted of a soil, representative of lands with dramatic water deficiency and very poor in organic matter content, supplied with a given amount (80 m(3) ha(-1)) of OMW as such (crude OMW, c-OMW) and after the removal of its toxic phenolic compounds (dephenolized OMW, d-OMW). Dephenolized OMW was produced in a soil-slurry stirred reactor containing an agricultural soil as catalyst. Several biochemical properties as well as the residual phytotoxicity of the soil with and without the two OMW amendments were monitored over time (0-42 days). The tested enzymes, as well as the microbial and chemical soil properties, showed different patterns in response to both crude and dephenolized OMW addition and time of incubation. As a general response several properties of the soil, mainly biological, changed suddenly or at the most within 0-14 days after the addition of the both kinds of OMW. Thereafter, most of them returned to their original values, showing the soil's resilience capability. As compared to c-OMW amendment, the addition of d-OMW to the soil resulted in a smaller impact onto soil performance as attested by the complete recovery of the soil germination capability, a less inhibitory effect of some enzymatic activity (urease) and higher values of the respiratory quotient qCO(2). The application of OMW, mainly after removal of its phenolic components, may be suggested as a good strategy for restoring soils in semiarid area and poor in organic matter. (C) 2010 Elsevier B.V. All rights reserved.