Nowadays, organic fertilizers such as biochar and manure in organic agriculture are widely used due to their considerable benefits. A new method should be provided to supply enough nutrients without polluting the environment. Converting animal waste to biochar was suggested as a sustainable agriculture practice to supply enough nutrients and improve soil quality. This study aims to assess the effect of poultry manure (PM) and its derived biochar (PM-BC), as well as time on distribution of soil phosphorous (P) fractions and release, along with phosphatase activity. Soil samples were treated with PM and PM-BC at three levels including 0.5%, 1%, and, 1.5% (w/w). Then, it was incubated at 25 °C with constant moisture equal to the field capacity (FC) for 140 days. In the next step, the soil samples were taken at time intervals of three hours for 1, 3, 7, 14, 28, 42, 63, 84, 112, and 140 days to evaluate the P fractions and phosphatase activity. In the next procedure, kinetic equations were fitted to the data. The results revealed a significant difference between both treatments. However, different levels of treatments did not affect the P concentration in exchangeable (EXC), carbonate (CAB), oxide (OX), and organically bound fractions significantly. On average, the highest contents in the EXC fraction were found in 1.5% of BC treatment (PM-BC) (23 mg kg-1). In addition, the lowest P concentration in EXC fraction was observed in the control soil (8.6 mg kg-1). The P content in the OX fraction increased up to the 28th day of the incubation and continued to decrease until its end. The highest P concentration in the OX fraction was found in 1.5% PM, which was about 71% more than the control soil. An increase in time decreased the organically bound fraction. The first order (R2 = 0.97 and 0.98; S.E. = 0.14 and 0.11 for PM and PM-BC, respectively) and power equation (R2 = 0.96 and 0.98; S.E. = 0.15 and 0.21 for PM and PM-BC, respectively) described the P release from different fractions appropriately. Unlike acid phosphatase activity, PM and PM-BC increased alkaline phosphatase activity. Based on the results, the manure was more effective than biochar. No significant difference was reported among various levels of treatments (0.5%, 1%, and 1.5%), indicating the cost-effectiveness of low treatment levels.
