Phytoavailability and extractability of potassium, magnesium and manganesein calcareous soil amended with olive oil wastewater

Land disposal of olive oil wastewater using it as a soil amendment requires a knowledge of the effects that its application may produce on the status of the mineral nutrients in the plant-soil system. A pot experiment using c alcareous soil was performed in a growth chamber to examine the effects of olive oil wastewater on the availability and postharvest soil extractabilit y of K, Mg and Mn. The experiment included 6 treatments: two rates of olive oil wastewater, two mineral fertilizer treatments containing K (which supp lied K in amounts equivalent to the K supplied by the olive oil wastewater treatments), a K-free mineral fertilizer treatment, and a control. The pots were sown with ryegrass as the test plant, harvesting 3 times at intervals of one month. Olive oil wastewater has demonstrated a considerable capacit y for supplying K that can be assimilated by the plant, tending in fact to surpass the mineral potassium fertilizer tested. The application of olive o il wastewater tends to reduce the concentration of Mg in the plant, similar ly to the effect of adding mineral potassium fertilizer. An enhancement of Mn availability takes place in the soil amended with olive oil wastewater, which on occasion has produced Mn concentrations in plant that could be con sidered phytotoxic or at least excessive. After harvesting, we observed an increase in the amount of exchangeable K in soil with added industrial wast ewater. However, these increases are lower than those in soil treated with mineral potassium fertilizer. The levels of exchangeable, carbonate-bound, organic-bound and residual Mg in soil were higher in treatments incorporati ng olive oil wastewater than in those with added mineral K, with the opposi te tendency occurring in the amount of Fe-Mn oxides-bound Mg in soil. Treat ments based on olive oil wastewater, especially in high doses, increased th e amount of exchangeable and carbonate-bound Mn in soil, in comparison with treatments adding mineral fertilizers with or without K. In contrast, the addition of industrial wastewater caused a drop in the amount of Fe-Mn oxid es-bound and organic-bound Mn in soil.