Effects of One-Time Long-Term Application of Organic–Inorganic Compound Fertilizer on Wheat Photosynthetic Characteristics, Soil Properties and Grain Yield

Wheat production demands simplified fertilization strategies to achieve sustainable high yields. This study evaluated the effects of the one-time high-rate application of an organic–inorganic compound fertilizer on soil properties, photosynthetic characteristics, and grain yields. A multi-year field experiment was conducted with a single basal application of an organic–inorganic compound fertilizer at 3600 kg·ha−1, using conventional split chemical fertilization as the control. Compared with the control, this treatment significantly increased soil organic matter and available nutrient content, enhanced the bacteria/fungi ratio, elevated soil enzyme activity, and promoted the conversion of humus into more stable forms. These improvements sustained a higher flag leaf photosynthetic capacity during the grain-filling stage and delayed leaf senescence. The multi-year average grain yield was 5.28% higher than that of conventional split fertilization. The one-time high-rate application of an organic–inorganic compound fertilizer can improve soil biological properties, maintain late-season photosynthetic function, and increase yields, serving as an effective technical measure for simplified, sustainable, and high-yield wheat cultivation in the region.