Effects of Straw Incorporation and Phosphorus Fertilization on Photosynthetic Characteristics, Dry Matter Accumulation, and Grain Yield of Maize

Maize (Zea mays L.) is a major cash and food crop in China and is critical to national food security. Straw returning improves soil physical properties by reducing bulk density and increasing porosity, while phosphate fertilization enhances soil P availability; their combined application can improve soil fertility and structure, creating favorable conditions for high yield. To evaluate this, we conducted a three-year field experiment (2023–2025) in the Tumochuan Plain irrigation area (Midwestern Inner Mongolia, China) with maize cultivar ‘Xianyu 335’. A control treatment (CK) without straw management and without phosphate fertilization was included for comparison. We examined the effects of two straw management practices (straw incorporation with deep tillage, SF; and surface straw mulching under no tillage, FG) and four phosphate fertilization rates (0, 80, 100, and 120 kg P2O5/ha) on photosynthetic characteristics, chlorophyll fluorescence, dry matter accumulation, and yield. S and P main effects were significant for all measured traits, including Fo; however, the S × P interaction was not significant for Fo, Fm, Fv/Fm, Ci, and yield. Compared with CK, all straw management treatments improved photosynthetic and chlorophyll fluorescence traits, increased dry matter accumulation, and enhanced grain yield. Straw incorporation with deep tillage consistently outperformed surface straw mulching under no tillage, and increasing phosphate fertilization rates enhanced the positive effects. Among the tested treatments and under the partial-budget assumptions, SFP120 (120 kg P2O5/ha) gave the highest yield (14,781.53 kg/ha), while SFP100 (100 kg P2O5/ha) had the numerically highest net profit (17,743.33 yuan/ha, ≈2546.17 USD/ha), 21.19 yuan/ha (≈3.04 USD/ha) above SFP120 (17,722.14 yuan/ha, ≈2543.15 USD/ha).