This study aimed to clarify the effects of straw return and phosphorus application rates on soil enzyme activity and yield formation of dryland wheat in western Henan. A split-plot experimental design was conducted from October 2020 to June 2022, using the wheat variety Luohan 22. The main plot treatments were based on maize straw return: no straw return (S0) and full straw return (S1). The sub-plot treatments included four phosphorus application rates: P0 (0 kg hm-2), P1 (75 kg hm-2), P2 (112.5 kg hm-2), P3 (150 kg hm-2), and P4 (187.5 kg hm-2). Soil enzyme activity, dry matter transport characteristics, grain filling dynamics, and yield and yield components were measured. The results showed that under the same phosphorus application rates, available phosphorus content and the activities of soil urease, sucrase, catalase, and alkaline phosphatase in the 0–20 cm and 20–40 cm soil layers, as well as key grain filling dynamics parameters (Vmax, Tmax, Wmax, Vmean, T1, and T2), were higher in the S1 treatment compared to S0. Similarly, under the same straw return treatment, these parameters initially increased and then decreased with increasing phosphorus application rates, with the highest values observed under the P3 treatment. In terms of dry matter transport, post-flowering dry matter assimilation and its contribution to grain in the S1 treatment were greater than in the S0 treatment. In the highest performing treatment (P3), these parameters showed significant increases of 38.67% and 5.76%, respectively. The interaction between straw return and phosphorus application rates had a significant impact on available phosphorus content, soil enzyme activities, dry matter transport characteristics, grain filling dynamics, and grain yield, with the highest values observed in the S1P3 treatment. Compared to S0P3, available phosphorus content and the activities of urease, sucrase, and catalase in the S1P3 treatment increased by 5.32%, 5.04%, 10.30%, and 2.92% in the first year, and by 7.37%, 3.88%, 11.64%, and 3.31% in the second year. Both straw return and increased phosphorus application rates improved spike numbers, grains per spike, thousand-grain weight, and overall grain yield. Except for thousand-grain weight, these indicators initially increased and then declined with increasing phosphorus rates under the same straw return treatment. Compared to S0P3, the S1P3 treatment significantly increased spike numbers and grain yield by 4.74% and 3.78% in 2020–2021, and by 9.06% and 4.51% in 2021–2022, respectively. S1P3 also significantly increased grains per spike by 5.25% in 2021–2022. In conclusion, full straw return combined with a phosphorus application rate of 150 kg hm?2 (S1P3) is an optimal cultivation practice for dryland wheat in western Henan and similar ecological regions.
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