initial retention of water by soil S1, the rainfall event washed away all chemicals, causing the increase of their concentration in the leachate, as discussed in Section 3.1. On the contrary, in soil S2 the higher permeability and the increase of leachate volume, due to irrigation and rainfall events around day 140, caused the dilution of all solutes characterizing OMW. Consequently, a slightly decreasing trend was detected for potassium concentration, that reached the lowest values, around 2 mg L 1, at the end of the test.