Abstract: To clarify the optimal phosphorus management strategy of wheat/maize rotation system under the condition of straw returning to the field, we set four levels of phosphorus application (P₂O₅), including P₀(0 kg·hm^-2), P₁(105 kg·hm^-2 for wheat and 63 kg·hm^-2 for maize), P₂(150 kg·hm^-2 for wheat and 90 kg·hm^-2 for maize), and P₃(195 kg·hm^-2 for wheat and 117 kg·hm^-2 for maize) in a long-term positioning experiment carried out in the typical fluvo aquic soil area of the North China Plain from 2011 to 2023. We investigated the effects of long-term phosphorus application on yield, phosphorus accumulation, transport, distribution characteristics and phosphorus balance in the wheat/maize rotation system under straw returning. The results showed that compared with P₀, the application of phosphorus fertilizer significantly increased the yield of wheat and maize, with the highest yield increase rates reaching 38.8% and 18.5%, respectively. The highest annual yield increased by was 25.9%. Among the three phosphorus application levels, P₁ had the best comprehensive effect. Compared with P₂ and P₃, P₁ significantly increased wheat, maize, and annual yield by 13.0% and 16.3%, 4.1% and 21.0%, 7.6% and 19.1%, respectively. The accumulation of post-anthesis dry matter increased significantly by 12.8% and 22.0% (wheat), 11.0% and 38.6% (maize), and the accumulation of post-anthesis phosphorus increased significantly by 94.5% and 177.4% (wheat), 46.8% and 146.2% (maize), respectively. The contribution rate of post-anthesis phosphorus to grain significantly increased by 39.3% and 81.4% (wheat), 24.4% and 65.4% (maize), respectively. The annual deficit of soil apparent phosphorus balance without phosphorus application for 12 consecutive years was 33.4 kg·hm^-2, while there was surplus under other phosphorus application levels. The phosphorus surplus in P₂ and P₃ during the wheat season was 2.0 and 2.7 times that of P₁, and it was 1.5 and 3.3 times that of P₁ respectively in the maize season. The relationship between wheat and maize yields and soil phosphorus surplus (P₂O₅) and available phosphorus content showed a parabolic trend. Calculated based on 95% of the maximum yield, the suitable available phosphorus and phosphorus surplus for wheat season soil were 15.5-24.3 mg·kg^-1 and 37.1-86.7 kg·hm^-2, respectively, while for maize season they were 12.4-18.5 mg·kg^-1 and 6.7-32.8 kg·hm^-2, respectively. In summary, moderate application of phosphorus fertilizer could improve soil phosphorus supply capacity, promote the accumulation and transport of dry matter and phosphorus in wheat and maize post-anthesis, increase yield and phosphorus fertilizer utilization efficiency, and reduce the risk of phosphorus leaching. The phosphorus application rate of 63.5-113.3 and 28.4-57.2 kg·hm^-2 in maize seasons is the best management strategy for wheat/maize rotation system to give consideration to yield and nutrient use efficiency and reduce environmental risks under the condition of straw returning in the loamy fluvo aquic soil region of the North China Plain.

Key words: wheat/maize rotation system, phosphorus level, accumulation and translocation of dry matter, phosphorus absorption and utilization, phosphorus balance