## 3 Results and Discussion
### Bio-Mixture Effect on Leachates Chemical Characteristics  
The results of the chemical analysis of the leachates from each bulk sample are presented in Figures 1-5. Regarding pH values, a slight decrease due to ion exchange processes was observed in the leachates of the bio-mixtures after the first application of the irrigation water compared to control soil pH values, but these values increased during subsequent irrigations and stabilized around eight, which is the same value as the control soil (Figure 1a). Acidic values of pH may consist of a hazard both for soil and groundwater when leaching occurs [30], but during the experiment, the pH of the leachate was always between seven and eight for all treatments. The raise of pH is in agreement with soil capacity to exchange cations, ensuing in hydrogen ion subtraction from the liquid phase. The electrical conductivity of all leachates decreased to 58% at the end of the experimentation. A decline in the EC values of all three bio-mixtures was observed during subsequent irrigations, in relation to the initial EC value of the control soil. Noteworthy is the fact that EC values of the first bio-mixture (biomix 1%) were slightly lower than those of the other two bio-mixtures. However, at the end of the irrigation applications they had about the same value (Figure 1b). The lessening tendency of electrical conductivity can be ascribed to the soil retention of the salts dissolved in the bio-mixture and especially since this was impregnated with olive mill wastewater (OMWW), in conjunction with the fact that dilution took place due to watering [30]. Concerning NO3\({}^{-}\) concentration, a decrease was noted in all leachates, possibly due to the mineralization of organic nitrogen and organic nitrogen degradation. It is observed that nitrate concentrations were higher in biomix 2% and biomix 3% compared to biomix 1%, ascribed to the fact that they consist of higher amounts of OMWW, in which nitrogen is mainly in the organic form and nitrate may accumulate in the soil after organic nitrogen mineralization by soil microorganisms [31]. At the end of the irrigation scheme, the NO3\({}^{-}\) concentration of bio-mixtures leachates was slightly elevated compared to the concentration  
Figure 1: Changes of: (**a**) pH values and (**b**) EC values in the leachates of the 10 irrigation applications of the four treatments. Each value is the mean of three replicates. Figure 2: Changes of: (**a**) NO3\({}^{-}\) (mg/L) concentrations and (**b**) B (mg/L) concentrations in the leachates of the 10 irrigation applications of the four treatments. Each value is the mean of three replicates. of the leachate of the control soil, and more specifically, a higher concentration was observed in the second bio-mixture (biomix 2%) (Figure 2a). As far as boron concentration, when bio-mixture was added to different percentages, boron values decreased in the leachates after the first irrigation, compared to control soil values, especially in the leachate of the third bio-mixture (biomix 3%). During subsequent irrigations there was a decrease in boron values, while at the end of irrigation, boron values of the second bio-mixture (biomix 2%) and the third bio-mixture (biomix 3%) were slightly higher than those of the first bio-mixture (biomix 1%) (Figure 2b). Regarding potassium concentrations, its values in the leachates gradually decreased during irrigation. Although in the beginning, potassium values were higher in the leachates of the three bio-mixtures after the first irrigation in relation to the control soil, at the end of the irrigation period, concentrations were at the same levels, with slightly increased values in the leachates of the second bio-mixture (biomix 2%) and the third bio-mixture (biomix 3%) (Figure 3a). The average potassium concentration eventually reaching the water table was always negligible regardless of the soil treatments.