Differences in Physicochemical Properties of Stems in Oat (Avena sativa L.) Varieties with Distinct Lodging Resistance and Their Regulation of Lodging at Different Planting Densities

Planting density is an effective strategy for regulating both <i>oat</i> lodging and forage quality. To delve into the regulatory mechanisms of planting density on lodging and <i>oat</i> forage quality, lodging-resistant variety LENA and lodging-sensitive variety QY2 were grown in 2018 and 2019 growing seasons, and four planting densities were implemented: 2.25 × 10⁶ plants/ha (D1), 4.5 × 10⁶ plants/ha (D2), 6.75 × 10⁶ plants/ha (D3), and 9 × 10⁶ plants/ha (D4). At the milk stage, we measured the contents of potassium, calcium, magnesium, silicon, lignin, crude fiber, starch, soluble sugar, and soluble protein in the second and third stem internodes of the plants. The results revealed the lodging-resistant variety LENA demonstrated significantly higher contents of calcium, potassium, silicon, crude fiber, lignin, and lower contents of starch, soluble sugar, and soluble protein (<i>p</i> < 0.01). Similar trends in the physicochemical properties of stem internodes for both <i>oat</i> varieties with increasing planting density. Crude fiber, soluble sugar, magnesium, starch, potassium, and lignin were the key characteristics affecting the lodging coefficient, and variety and planting density affected the lodging coefficient mainly by regulating the synthesis of starch, soluble sugar, and crude fiber. At planting density D3, stem internodes exhibited higher physicochemical properties and a lower lodging coefficient, favoring <i>oat</i> forage production. The results offer a valuable theoretical foundation and practical reference for <i>oat</i> lodging-resistant cultivation.