Photosynthesis-driven yield improvement in maize under sulfur application: role of young ear development and grain filling

BACKGROUND: Sulfur (S) deficiency is increasingly recognized as a limiting factor for maize productivity, yet the physiological mechanisms underlying sulfur-driven yield enhancement remain insufficiently understood. This study aimed to clarify how sulfur application influences maize ear development, grain filling, and photosynthetic performance. RESULTS: Field experiments were conducted during 2020–2021 on two contrasting soil types (black soil and sandy soil) with sulfur application rates ranging from 0 to 120 kg ha⁻¹. Moderate sulfur application (S60–S90) significantly increased maize grain yield (P < 0.05), with yield increases of approximately 10–27% in black soil and 7–26% in sandy soil, and peak yields of 11,843 kg ha⁻¹ and 8,780 kg ha⁻¹, respectively, at the S90 treatment. Yield improvement was primarily attributed to coordinated increases in kernel number per ear and thousand-grain weight. Kernel number per ear increased significantly by 2.7–6.8% in black soil and 2.0–7.4% in sandy soil, which was closely associated with enhanced nitrogen accumulation in young ears (12.1–46.1% higher than S0) and increased fertilization rates (1.0–2.3%). Thousand-grain weight was also significantly improved, increasing by 1.2–11.9% in black soil and 3.8–16.7% in sandy soil, supported by higher grain-filling rates (0.7–1.9 g day⁻¹ per thousand-grain) and a prolonged rapid grain-filling duration (0.5–1.9 days). In addition, sulfur application significantly maintained post-silking photosynthesis by increasing chlorophyll content and leaf area index, thereby ensuring sufficient assimilate supply for kernel development. CONCLUSIONS: Sulfur fertilization improves maize yield by coordinating pre-silking ear development and nitrogen uptake with post-silking photosynthetic activity to support grain filling. These findings provide a physiological framework for nutrient management strategies to optimize maize yield under variable soil fertility conditions.