Abstract: Excessive water and chemical fertilizer application is often reported in North China winter wheat-summer maize rotation systems, resulting in economic losses and environmental issues. Therefore, optimizing water and nutrients (e.g., P) for crop yield is important. A 3-year field lysimeter experiment was performed on Lou soil (loess-derived and developed on natural cinnamon soil) in Yangling, Shaanxi Province, Northwest China, to investigate P use efficiency and P leaching of winter wheat-summer maize rotation systems in cinnamon soil. Seven treatments were used to investigate crop yield, P partial productivity (PFP_P), and P leaching: conventional practices (CP1, lysimeter depth = 120–150 cm; CP2, lysimeter depth = 100 cm), CP1 plus reduced water supply (CP1-W), CP1 plus reduced nutrient supply (CP1-F), CP1 plus reduced water and nutrient supplies (OPT), CP2 plus biochar application (CP2+B), and OPT plus biochar application (OPT+B). The results showed that the mean wheat, maize, and total wheat + maize yields were similar among CP1, CP1-W, CP1-F, and OPT. Compared with CP1, CP1-F and OPT significantly increased PFP_P by an average of 69.3% and 56.4%, respectively. CP1-W and CP1-F did not affect P leaching, but annual particulate phosphorus leaching decreased significantly under OPT treatment (by 58.4%). Biochar use did not affect the mean annual crop yield, but CP2+B significantly increased PFP_P (by 43.6%) compared with CP2. OPT-B did not affect PFP_P compared with OPT. Each year, all forms of leached P were similar between CP2 and CP2+B. In the first treatment year, OPT+B significantly decreased (compared with OPT) the dissolved organic phosphorus, particulate phosphorus, and total phosphorus (TP) leaching losses by 60.0%, 57.1%, and 62.4%, respectively, but TP leaching increased significantly in the following 2 years. The 3-year average showed that biochar application did not affect P loss. Therefore, only reducing water and fertilizer applications to cinnamon soil may improve P use efficiency and reduce P leaching while maintaining crop yield. Applying wheat straw biochar did not affect crop yield or P leaching, and the effect on PFP_P was inconsistent. Further studies are needed to clarify the effectiveness of biochar application.