Abstract: Abstract: Phosphorus has been one of the most limiting factors to food security in modern agriculture, due to the nonrenewable natural resource. This study aims to investigate the effects of irrigation and fertilization schedules on the phosphorus absorption, transformation, and use efficiency in paddy fields. A systematic evaluation was made on the contribution to the phosphorus availability of rice in the paddy soil. Taking the hybrid indica rice Zhongzheyou 1 as the experimental material, two irrigation schedules were set, including the conventional flooding and alternate wet/dry (AWD) irrigation. Five types of nitrogen application were the zero fertilizer (CK), traditional nitrogen level (100% PU), 80% of traditional nitrogen level (80% PU), 80% of control-released nitrogen fertilizer plus biochar (control released fertilizer, 80% CRF + BC), and 80% of stable compound nitrogen fertilizer plus biochar (stable fertilizer, 80% SF + BC). An analysis was performed on the rice yield and phosphorus absorption efficiency, as well as the contents of soil available phosphorus, and the composition of the various phosphorus forms. The results showed that: 1) The AWD irrigation under various treatments significantly increased the rice yield (P<0.05), compared with the CF schedule. The maximum yields of 9 656.2 and 1 0032.4 kg/hm2 were achieved in the 80% CRF+BC and 80% SF+BC treatments, respectively. All yields here were also significantly higher than those in the 100% PU and 80% PU treatments. 2) The AWD also significantly improved the content of phosphorus that accumulated in the panicle at the maturity stage of rice in the 80% SF+BC treatment. The phosphorus accumulation in the different organs of rice, the absorption efficiency, and partial factor productivity were all significantly higher in the 80% CRF+BC and 80% SF+BC treatments than those in the 80% PU one; 3) There were the higher contents of soil available phosphorus, inorganic/organic phosphorus, and soil phosphorus activated coefficient at the depth of 0-15 cm and >15-30 cm in the 80% CRF + BC and 80% SF + BC treatments, including the moderately labile organic phosphorus (MLOP), and labile organic phosphorus (LOP) at the depth of 0-15 cm, compared with the 100% PU and 80% PU treatments; 4) A correlation analysis showed that there was the largest direct path coefficient of available phosphorus with the moderately resistant organic phosphorus (MROP, 0.599). The direct path coefficient with the LOP and MLOP, Ca-, Al- and O-Phosphate were 0.248, 0.177, -0.169, 0.126, and -0.079, respectively. It indicated that the MROP, LOPs, MLOP, and Al-Phosphate were the main decision-making factors for the soil available phosphorus, whereas, the Ca- and O-phosphate were the limiting factors for the available phosphorus. Correspondingly, an effective way can be expected to increase the content of MROP, LOP, and MLOP under the appropriate water and fertilizer management, further to increase the soil available phosphorus. Furthermore, the phosphorus uptake and use efficiency of rice can be achieved for the better transformation and activity of soil phosphorus at the mature stage of rice under the suitable AWD irrigation, control-released nitrogen fertilizers, or stable compound nitrogen fertilizer plus biochar in paddy fields.