Effect of organic fertilizer substitution on soil fertility and yield in a continuous maize cropping system: evidence from an eight-year long-term field experiment

Introduction: exchange during maize grain filling. Methods: exchange rate (NCER), and maize yield in a continuous maize cropping system. Four treatments with equivalent nutrient inputs were established: no fertilization (CK), conventional chemical fertilization (NP), one-third substitution of chemical fertilizer with commercial organic fertilizer (1/3M), and sole application of commercial organic fertilizer (M). Leaf photosynthetic traits, canopy structure, soil water content, and soil NCER were measured at the early, middle, and late grain-filling stages, while soil physicochemical properties, yield components, and plant nutrient contents were determined after harvest. Results: Fertilization significantly altered the nutrient pool structure of the Sierozem. Compared with CK, NP markedly increased soil available phosphorus and total phosphorus, whereas M significantly increased soil organic matter, total nitrogen, and available potassium, but also raised soil electrical conductivity. By contrast, 1/3M achieved a more coordinated improvement in soil nutrient status while maintaining stable soil pH. Although canopy function gradually declined with grain-filling progression, NP and 1/3M maintained significantly higher photosynthetic capacity than CK during the middle and late stages. Soil NCER showed clear stage-dependent variation, peaking at the middle grain-filling stage, and was significantly enhanced by fertilization, with 1/3M increasing NCER by 107.3% at the middle stage and by 145.6% at the late stage relative to CK. Maize yield was highest under 1/3M, increasing by 143.0% relative to CK. Discussion: Overall, canopy function during grain filling was closely coordinated with soil NCER and yield formation, and one-third substitution of chemical fertilizer with organic fertilizer was the most effective strategy for improving soil fertility, sustaining canopy function, stabilizing carbon processes, and increasing yield.