Double-season full straw incorporation enhances maize yield by regulating soil nutrients and promoting above-ground growth in lime concretion black soil

Straw incorporation is a vital residue management strategy that improves soil structure, enhances crop yields, and promotes sustainable agriculture. However, its long-term effects on soil nutrient balance and subsequent maize development in lime concretion black soil remain insufficiently explored. Drawing on a long-term experiment established in 2008, we evaluated four straw incorporation regimes: no straw incorporation (CK), single-season full maize straw incorporation (W0M1), single-season full wheat straw incorporation (W1M0), and double-season full wheat and maize straw incorporation (W1M1). We assessed their impacts on soil nutrients, maize growth, leaf photosynthesis, and yield during the 2024–2025 growing seasons in lime concretion black soil. The results demonstrated that straw incorporation treatments and inter-annual variation significantly affected soil nutrient, maize growth, and final yield. Specifically, straw incorporation significantly increased the contents of soil nitrogen, phosphorus, potassium, and organic matter across all growth stages, and elevated the soil nutrient balance index (SNB) by 12.50%–24.44% at the R6 stage. In addition, straw incorporation significantly promoted maize development, with the W1M1 treatment demonstrating the optimal effect; its dry matter accumulation and functional leaf area at the R1 stage increased by 13.06%–14.18% and 24.71%–24.76%, respectively, compared to CK. Furthermore, by improving the physiological characteristics (SPAD values, Rubisco and PEPC enzyme activities) and photosynthetic parameters ( P n , C i , and g s ) of functional leaves, straw incorporation significantly increased the maximum photosynthetic ( Anmax ) rate at the R1 and R3 stages (by 10.91%–18.87%), and enhanced post-silking assimilate accumulation and grain yield. Partial least squares structural equation modeling (PLS-SEM) further elucidated the correlation pathways among the variables: both SNB （ P < 0.05） and soil organic matter content （ P < 0.001） were closely related to leaf physiological characteristics, while photosynthetic performance was jointly driven by soil water content and physiological status. In summary, all straw incorporation regimes effectively enriched soil nutrients, optimized maize source-sink dynamics, and enhanced leaf photosynthetic traits and grain yield, with W1M1 exhibiting the most pronounced effects. This study provides new insights and a theoretical basis for soil amelioration and stable maize production in the lime concretion black soil region.