Due to the increasing population and the raise of per capita demand for agricultural products and the lack of possibility of a significant increase in farmable lands, application of a variety of chemical fertilizers has been increased in order to recover the power of soil to supply nutrients needed by plants. However, overuse of chemical fertilizers has undesirable effects on the environment and the natural ecosystem balance. Therefore many researchers have recommending using of organic fertilizers instead of chemical fertilizers in arable lands. Biochar, a carbon rich material made by heating organic matter in low oxygen conditions, is a valuable soil amendment that can be used to improve chemical, physical, and biological properties of soils. In the present study biochar produced from bagasse (cane scum) in two pyrolysis temperatures of 350 and 600 °C was used as an organic oil conditioner. An acidic and a calcareous soil were sampled from Isfahan and Gilan provinces, respectively, and treated with the biochar with four levels of 0, 1, 3, and 6% w/w. Then the samples were incubated at 25 °C and 80% field capacity for 30 d. ubsequently, the effects of biochar amendment on some chemical properties of the soils were studied. Also, effects of the biochar application on phosphorus (P) intensity-quantity relationships were examined in both acidic and calcareous soil. The results showed that biochar has an alkaline pH, high interior surface area and plant nutrients. Application of biochar in acid soils increased soil pH, EC, CEC, as well as concentrations of nutrients and heavy metals. Application of biochar also increased these characteristics in the calcareous soil, but its impact on pH was less than that that in acid soil. The P intensity-quantity (Q/I) relationships in the acid soil were fitted well by the Langmuir, Freundlich, Van Huay, and linear models. In the case of the calcareous soil, the Langmuir, linear and Van Huay models were adequately fitted the P Q/I data. Overall, P buffering capacity indices decreased by the application of biochar in acid soil, suggesting an easier release of P from the solid phase to the solution for plant uptake. In the calcareous soil, however, P buffering capacity indices increased by biochar addition, suggesting that the ease of P release from the soil to the solution decreased due to biochar addition. Keywords : Biochar, Soil Phosphorus, Intensity index, Quantity index, Buffering capacity inde