Changes Induced by Olive Mill Wastewaters Used as Organic Fertilizer on Polyphenol Content, pH and Salinity of an Alkaline Soil

Aims: The main objective of this paper is to determine the recommended amounts of olive mill wastewaters (OMW) that should be applied as a fertilizer in alkaline soil, based on evolution of its pH, salinity and polyphenol content.
Study Design: Randomized complete block design with three replications where the variable factor was amount of OMW.
Place and Duration of Study: The trial was carried in an open glass greenhouse in the Regional Agricultural Research Center of Meknes - Morocco, between February and March 2012.
Methodology: Four amounts of OMW (50, 75, 100 and 150 m3/ha) were tested as organic fertilizer on an alkaline soil in comparison with water treatment based on measurement of soil pH, electrical conductivity and polyphenol content using fenugreek as an indicator plant. The Indicators of stress measured on plants were leaf chlorophyll content, stomatal conductance and leaf temperature.
Results and Discussion: The application of the four amounts of OMW induced a decrease of soil pH and an increase of its electrical conductivity whereas soil polyphenol content following significant regression models. Soil pH and electrical conductivity changed slightly under all treatments with a maximal values under the treatment 150 m3/ha. However, soil polyphenol content increased widely under different treatments of OMW. The physiological parameters of the fenugreek showed a certain stress under 150 m3/ha.
Conclusion: OMW may be used as organic fertilizer up to 100 m3/ha on alkaline soil without adversely affecting its quality in the arable layer. Beyond this amount, a particular attention should be paid, to soil polyphenols as far as their phytotoxicity is concerned, since a high concentration of polyphenols may exert an allelochemical effect.