Coupling Effects of Straw Return and Fertilization Regime on the Photosynthesis-Soil-Yield Continuum of Spring Maize...

Long-term straw return combined with optimized fertilization represents a effective strategy to enhance soil quality and crop productivity in cold regions, yet its integrated effects on the photosynthesis-soil-yield continuum of spring maize remain unclear, particularly under conditions of low accumulated temperature and slow straw decomposition. Based on a 9-year field experiment (2017-2025) conducted in the cold spring maize zone of Northeast China, this study investigated five treatments: CK, CF, CK + S, CF + S, and OPT + S. Photosynthetic parameters at four growth stages, soil nutrients, and grain yield were systematically measured. The results showed that OPT + S achieved the highest grain yield (15,016.11 kg·ha^-1 in 2025) and maintained superior photosynthetic performance throughout the growing season, with a photosynthetic decline rate of only 37.21% during the grain-filling stage-significantly lower than that of CK (48.20%). Soil available phosphorus (AP) and available potassium (AK) were significantly increased under straw return treatments (CK + S, CF + S, OPT + S). Correlation and stepwise regression analyses identified AP and net photosynthetic rate at the jointing stage (PnJ) as the key drivers of yield, jointly explaining 84% of yield variation. These findings demonstrate that the OPT + S treatment optimizes the coupling among early-stage photosynthesis, soil nutrient availability, and grain yield, providing a practical and high-yielding nutrient management strategy for spring maize in cold regions.