Biochar prepared from corn stalks is used as a source of phosphorus in this study. The hypotheses were to investigate effects of biochar applications in clay soil on availability, changes of phosphorus pools and maximum adsorption of phosphorus as well as corn growth. The soil was placed in plastic pots with each contains 3 kg of this soil. Biochar was added at levels of 0 (control), 6.5 (B1), 19 (B2), and 38 (B3) g pot−1. In this experiment, the pot was planted with corn (Zea mays). The results of this study revealed that the biochar application enhanced available phosphorus (Olsen-P) from 11.51 to 17.10 mg kg−1. Adding biochar significantly increased the amount of NH4Cl-P, NaHCO3-Po, and NaOH I-Po fractions (p ≤ 0.05), but it significantly decreased HCl-Pi fraction (p ≤ 0.05). Addition of biochar at the highest level increased the fresh and dry matter productions by up to about 75 and 48.7%, respectively, compared to the control. The phosphorus uptake by corn plants significantly increased with increasing levels of biochar. The removal efficiency (% sorption) and maximum adsorption (b) of phosphorus increased with increasing level of biochar addition compared to control. Consequently, it is recommended to add biochar produced from corn stalks to the soil in order to substitute phosphate fertilizers.