Long-Term Straw Return Combined with Tillage Management Systems Enhances Photosynthetic Capacity, Antioxidant Defense System, and Maize Yield

Intensive maize production generates large quantities of crop residues, and the widespread practice of open-field straw burning poses serious environmental challenges. Sustainable agricultural intensification therefore requires effective residue management and tillage strategies that maintain crop productivity while minimizing environmental impacts. This study evaluated the effects of straw return (incorporation of chopped maize straw) versus straw removal, combined with four tillage practices: no-tillage (NT), rotary tillage (RT), sub-soiling (SS), and sub-soiling plus rotary tillage (SS + RT), on maize growth and yield in a subtropical double-cropping system in southern China. The results demonstrated that straw return significantly increased chlorophyll content and the net photosynthetic rate (Pn), while delaying the decline in leaf greenness and CO2 assimilation during the late growing season. Straw incorporation also enhanced the antioxidant defense system, increasing catalase (CAT) activity by approximately 34% and superoxide dismutase (SOD) activity by about 12% on average, while reducing oxidative damage compared with straw removal. Among the tillage treatments, SS-RT consistently produced the greatest improvements in photosynthetic performance and antioxidant enzyme activities, resulting in higher dry matter accumulation and grain yield. The combined application of straw return and SS-RT achieved the highest kernel number, 1000-kernel weight, and grain yield, increasing yield by up to 17% compared with no-tillage. These findings indicate that integrating straw return with a combined deep- and shallow-tillage system effectively enhances photosynthetic capacity, strengthens antioxidant defense, and improves maize productivity, providing a practical management strategy for intensive maize production.