Optimized nitrogen fertilizer management to balance lodging resistance and stem physicochemical properties of oats

Background Oat ( Avena sativa L.) serves as a vital dual-purpose crop for grain and forage; however, its production potential is frequently compromised by stem lodging resulting from improper nitrogen (N) management. Although the physiological basis of lodging is established, the precise quantitative contribution of specific stem characteristics under varying N regimes remains underexplored. To bridge this gap and optimize N strategies, we conducted a two-year field trial (2018–2019) in the rain-fed Qinghai-Tibet Plateau using two cultivars with contrasting lodging resistance: LENA (resistant) and QY2 (susceptible). Under six N gradients (0, 60, 120, 180, 240, and 300 kg·ha⁻¹), we quantified structural polymers (lignin, cellulose, starch), non-structural carbohydrates (soluble sugars), and mineral elements (Ca, K, Si, Mg) in the second basal internode at the milk stage. Data were analyzed using hierarchical partitioning, Structural Equation Modeling (SEM), and the TOPSIS method to identify key determinants of stem strength. Results Lodging severity and stem physio-chemical profiles were significantly modulated by N dosage, genotype, and their interaction. Escalating N input marked elevated soluble protein levels while concurrently depressing the concentrations of lignin, cellulose, and key minerals (Si, Ca, K). Hierarchical partitioning analysis pinpointed Ca, K, Si, soluble sugars, and lignin as the predominant drivers, collectively accounting for 87% of the variation in the lodging index. Furthermore, SEM elucidated the regulatory pathways: genotype and N fertilization (including their interaction) indirectly exacerbated lodging risk by suppressing the accumulation of these structural and mineral components. The total standardized effects on the lodging index were recorded as -0.209 (genotype), 0.31 (N rate), and 0.156 (interaction). Conclusions Based on the comprehensive production and lodging resistance performance, it is recommended that in the rain-fed area of the Qinghai-Tibet Plateau, the suitable nitrogen application rate of the lodging-resistant variety LENA should be 180 kg·hm ^− 2 , while that of the lodging-prone variety QY2 should be controlled below 60 kg·hm ^− 2 . These findings provide a physiological framework for rational nitrogen management and offer novel mechanistic insights into oat lodging resistance.