Abstract
The land spreading of olive mill wastewater (OMW) derived from olive oil production can represent a suitable option to enrich and maintain agriculture soils under south Mediterranean climates. Therefore, OMW spreading field may represent a low cost contribution to crop fertilization and soil amendment. The main objective of this study was to investigate the long-term effects of raw OMW application on soil macronutrients and phenolic compounds dynamics. The results showed that regular application of three doses: 50, 100 and 200 m3·ha-1 of OMW for nine successive years increased the soil electrical conductivity significantly (p ≤ 0.05%) with the increase of OMW rates at the depth 0 - 20 cm. The pH variations were not detected after ten months of the spreading date. Furthermore, soil sodium adsorption ratio (SAR) and exchangeable sodium percentage (ESP) values were substantially affected by OMW salinity. The soil organic matter (SOM) increased from 0.068% observed for the control sample to 0.2%, 0.34% and 0.48%, respectively, with the increase of OMW rate in the top layer (0 - 20 cm). The potassium, phosphorus and nitrogen increased gradually with the OMW application dose. The Ca2+ contents on soil decreased with the spreading of OMW rate, as referred to control. In addition, the phenolic compounds variations were not proportional to doses applied and its levels remained high as compared with the control essentially on top layers (0 - 40 cm). This practice should be beneficial to organic farming and is an alternative solution to direct spreading of raw OMW on soil.
Highlights
Mediterranean countries are the major world producers of olive oil with 2,205,300 t produced by EU member states in 2011 [1]
A long-lasting repeated oil mill wastewater (OMW) spreading determined the impact of long-term on soil physico-chemical parameters: pH, electrical conductivity (EC), soil organic matter (SOM), Na+, K+, Ca2+, Mg2+ and polyphenols contents in comparison with the control
The yearly application of three OMW doses (50, 100 and 200 m3∙ha−1) for 9 successive years improved the fertility of Tunisian sandy soil, offering the opportunity to recycle the various compounds
Summary
Mediterranean countries are the major world producers of olive oil with 2,205,300 t produced by EU member states in 2011 [1]. OMW contains large amounts of suspended solids and high concentrations of polyaromatic compounds e.g. simple phenols and flavonoids, or polyphenols from 0.5 to 24 g∙L−1 [8]-[11] while it cannot be directly disposed into domestic wastewater treatment. This effluent has a high potassium level and notable concentrations of sodium, phosphorus, calcium and magnesium [3]
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