18. Short-Term Effects of Olive Mill Wastewater Spreading on Chemical Properties of Soils in Arid Lands, Study Case from Southern Tunisia

Olive mill wastewater (OMW) is occurred from the production of olive oil in olive mills. Many olive mills are scattered in most Mediterranean countries which produce it seasonally. This led to an environmental problem in these olive oil-producing countries, due to the elevated level of salinity, polyphenols, and the pollution burden. However, OMW is also characterized by richness in organic and mineral compounds. Consequently, OMW spreading can be an alternative for a low cost soil organic amendment. This work aimed to study the effect of OMW spreading on the chemical properties of soils in arid regions. Amendments with OMW were applied on two different soils in arid regions from Southern Tunisia with a quantity of 300 L per 100 m² (per plot), in a completely randomized experimental setup. The main objective of this work is to identify the short-term effect of OMW on fertility of sandy soil, for the supply of soil on organic carbon, inorganic nitrogen, available phosphorus and exchangeable potassium during 2010 as well as assessment of its effect on pH, salinity of soils in arid regions. Obtained results show that under the conditions of our experiment, applying of this organic effluent has changed significantly the content of exchangeable potassium (197% and 221%, respectively, for Dar Dhaoui (A) and El Fje (B) soil), mineral nitrogen, phosphorus (370% and 445%, respectively for (A) and (B) soil), and organic matter in soil (from 0.92% to 1.51% and from 0.87% to 1.95%, respectively, for (A) and (B) soil). Consequently, OMW is considered as a rich organic material and may constitute a potential potassic amendment for dryland soils poor in this element, which has the tendency to increase the content of major elements and the soil organic matters. OMW application did not cause a significant change in soil pH, due to the low quantity of OMW used in the soil. However, we highlighted the value of OMW as an organic amendment that requires further study on optimizing used doses to avoid the possible risks. According to the obtained results we can confirm that OMW can be very useful as an organic amendment in agriculture.