The Effect of the Interaction of Nitrogen Fertilization with Planting Density on Maize (Zea mays L.) Yield, Stalk Mechanical Properties, and Enzyme Activity

This study examines the effects of nitrogen-planting density interactions on stalk lodging resistance mechanisms and yield formation in spring maize (<i>Zea mays</i> L.), aiming to establish a theoretical framework for optimizing planting configurations to achieve high and stable yields in Shanxi Province. Using the maize variety Qiangsheng 192 as the experimental material, a split-plot field experiment was conducted from 2023 to 2024. Planting density served as the main plot, with three levels: 60,000 plants ha^-1 (M1, 6 plants m^-2, control), 75,000 plants ha^-1 (M2, 7.5 plants m^-2), and 90,000 plants ha^-1 (M3, 9 plants m^-2), each replicated three times. Nitrogen application rate was the subplot, with four treatments: N0 (0 kg ha^-1), N1 (90 kg ha^-1), N2 (180 kg ha^-1), and N3 (270 kg ha^-1). At the tasseling stage, agronomic traits and mechanical properties of the stalks were investigated. The activities of Phenylalanine Ammonia-Lyase (PAL), Tyrosine Ammonia-Lyase (TAL), and Cinnamyl Alcohol Dehydrogenase (CAD) in the stalks were measured at the big trumpet stage, tasseling stage, filling stage, and maturity stages, and yield was determined. The results showed that the M2 treatment achieved the highest yield, followed by M3, while M1 (control) had the lowest yield. Under the M2N2 configuration, the yield reached 13.55 Mg ha^-1, the highest recorded. As planting density increased, maize growth exhibited variations: the basal internodes elongated, mechanical properties declined, and the activities of PAL, TAL, and CAD enzymes decreased. Increased nitrogen application improved basal internode quality. Correlation analysis revealed that stalk mechanical properties were positively correlated with PAL, TAL, and CAD enzyme activities, which could both reflect the quality of the stalk. In conclusion, the M2N2 configuration is an optimal combination for enhancing maize yield, improving stalk mechanical properties, and increasing enzyme activity, making it suitable for large-scale application in the dryland spring maize areas of Shanxi Province.