The objective of this study was to examine the effect of adding modified bone char, bone char with sulfur and humic acid on some chemical properties and phosphorus availability in calcareous sandy soil. This experiment consisted of twelve treatments, viz, control (CK), bone + sulfur (B+S), bone + humic acid (B+HA), bone char + sulfur (BC+S), bone char + humic acid (BC+HA), modified bone char (MBC), modified bone char + humic acid (MBC+HA), bone char acidified with 0.1 N sulfuric acid (0.1ABC), bone char acidified with 1 N sulfuric acid (1ABC), phosphate rock (RP), phosphate rock + sulfur (RP+S), phosphate rock + humic acid (RP+HA). This experiment was incubated for 0, 7, 15, 30, 60, and 90 days under laboratory conditions. At the end of the incubation period, adding B+S, B+HA, BC+S, BC+HA, MBC, MBC+HA, 0.1ABC, 1ABC, RP+S, and RP+ led to a significant increase in available phosphorus compared to the control. The results obtained from this study revealed that the highest contents of phosphorus released from bone char were observed in BC+S, MBC+HA, and MBC treatments. In addition, available P in the soil increased with increasing incubation time. Soil pH significantly decreased with increasing incubation periods under adding B+S, B+HA, BC+S, BC+HA, MBC, MBC+HA, RP, RP+S, and RP+HA compared to the control. Accordingly, we can suggest applying bone char with sulfur as an alternative and safe source of phosphate fertilizers in sustainable agriculture