Concurrent increases in planting density and potassium fertilizer application rate: an effective strategy for enhancing grain yield and improving lodging resistance in summer maize

1. Concurrent increases in planting density and potassium fertilizer application rate enhanced the activity of lignin biosynthesis-related enzymes, promoting the synthesis and accumulation of lignin and cellulose. 2. This also led to thicker stems and more developed root systems, improving plant structural support and mechanical stability. 3. This approach achieved simultaneous improvements in both grain yield and lodging resistance in summer maize. Increasing planting density is an effective strategy for enhancing the yield potential of summer maize; however, it substantially elevates the risk of lodging under adverse weather conditions such as heavy rainfall and strong winds. Under these circumstances, potassium fertilizer plays a progressively critical role in improving lodging resistance. Previous studies have primarily focused on the individual effects of planting density and potassium fertilizer application rate on maize lodging resistance and yield, with less emphasis on their integrative effects in the lodging resistance process. In this study, two maize varieties differing in lodging resistance—Denghai 605 (DH605, lodging-resistant) and Xianyu 335 (XY335, lodging-susceptible)—were used as experimental materials. Three treatments were established: T1 (density, 67,500 plants ha −1 ; K 2 O, 180 kg ha −1 ), T2 (density, 82,500 plants ha −1 ; K 2 O, 180 kg ha −1 ), and T3 (density, 82,500 plants ha −1 ; K 2 O, 270 kg ha −1 ), to examine the mechanism through which concurrent increases in planting density and potassium fertilizer application rate affect lodging resistance and yield formation of summer maize. In terms of yield improvement, the T3 treatment demonstrated a significant advantage, increasing the two-year average yield of DH605 and XY335 by 18.65 and 16.05%, respectively, compared to T1, and by 7.25 and 14.36% relative to T2. In terms of lodging resistance, T3 promoted stem thickening and root system expansion while enhancing the activity of lignin biosynthesis-related enzymes (PAL, TAL, and CAD) in both stems and brace roots. This facilitated increased synthesis and accumulation of lignin, thereby strengthening mechanical properties. Consequently, the T3 treatment reduced lodging rate by 30.45% (DH605) and 29.42% (XY335) compared to T1, and by 51.21 and 55.90% compared to T2. Overall, concurrent increases in planting density and potassium fertilizer application rate achieved dual improvements in both yield and lodging resistance in summer maize. This approach provides a crucial reference for mitigating lodging risks under projected extreme weather events and ensuring high and stable production of summer maize.