In the present work, the olive mill solid waste (OMSW)-derived biochar (BC) was produced at various pyrolytic temperatures (300-700˚C) and characterized to investigate its potential negative versus positive application effects on pH, electrical conductivity (EC), and nutrients (P, K, Na, Ca, Mg, Fe, Mn, Zn, and Cu) availability in a calcareous loamy sand soil. Therefore, a greenhouse pot experiment with maize (Zea mays L.) was conducted using treatments consisting of a control (CK), inorganic fertilizer of NPK (INF), and 1% and 3% (w/w) of OMSW-derived BCs. The results showed that BC yield, volatile matter, functional groups, and zeta potential decreased with pyrolytic temperature, whereas BC pH, EC, and its contents of ash and fixed carbon increased with pyrolytic temperature. The changes in the BC properties with increasing pyrolytic temperatures reflected on soil pH, EC and the performance of soil nutrients availability. The BC application, especially with increasing pyrolytic temperature and/or application rate, significantly increased soil pH, EC, NH 4 OAc-extractable K, Na, Ca, and Mg, and ammonium bicarbonate-diethylenetriaminepentaacetic acid (AB-DTPA)-extractable Fe and Zn, while AB-DTPA-extractable Mn decreased. The application of 1% and 3% BC, respectively, increased the NH 4 OAc-extractable K by 2.5 and 5.2fold for BC300, by 3.2 and 8.0-fold for BC500, and by 3.3 and 8.9-fold for BC700 compared with that of untreated soil. The results also showed significant increase in shoot content of K, Na, and Zn, while there was significant decrease in shoot content of P, Ca, Mg, and Mn. Furthermore, no significant effects were observed for maize growth as a result of BC addition. In conclusion, OMSW-derived BC can potentially have positive effects on the enhancement of soil K availability and its plant content but it reduced shoot nutrients, especially for P, Ca, Mg, and Mn; therefore, application of OMSW-derived BC to calcareous soil might be restricted.

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36In this study, a greenhouse pot experiment with maize (Zea mays L.) was conducted using treatments 37 consisting of a control (CK), inorganic fertilizer of NPK (INF), and 1% and 3% (wt/wt) of olive mill solid 38 waste (OMSW)-derived biochar (BC) at various pyrolytic temperatures (300-700 °C). The goal was to 39 investigate potential negative versus positive effects of BC on pH, electrical conductivity (EC), and 40 nutrient (P, K, Na, Ca, Mg, Fe, Mn, Zn, and Cu) availability in a calcareous loamy sandy soil. The results 41 showed that application of OMSW-derived BC, especially with increasing pyrolysis temperature and/or 42 application rate, significantly increased soil pH, EC, NH 4 OAc-extractable K, Na, Ca, and Mg, and 43 ammonium bicarbonate-diethylenetriaminepentaacetic acid (AB-DTPA)-extractable Fe and Zn, while 44 AB-DTPA-extractable Mn decreased. The application of 1% and 3% BC, respectively, increased the 45 NH4OAc-extractable K by 2.5 and 5.2-fold for BC300, by 3.2 and 8.0-fold for BC500, and by 3.3 and 46 8.9-fold for BC700 compared with that of untreated soil. The results also showed significant increases in 47 shoot content of K, Na, and Zn, while there were significant decreases in shoot content of P, Ca, Mg, and 48 Mn. Furthermore, no significant effects were observed for growth of maize plants as a result of biochar 49 BC addition. In conclusion, OMSW-derived BC can potentially have positive effects on the enhancement 50 of soil K availability and its plant content but it reduced shoot nutrients, specifically P, Ca, Mg, and Mn; 51 therefore, application of OMSW-derived BC to calcareous soil might be restricted. 52