Under intensified global climate change and anthropogenic pressures, alpine ecosystems confront unprecedented stress. The degradation of alpine meadows has caused significant declines in productivity and in the abundance of high-quality forage species. This study aims to explore the effects of phosphorus (P) application and reseeding of Medicago ruthenica (L.) Trautv. on the biomass and quality of forage in degraded alpine meadows, and to identify the key soil factors influencing forage growth. Three reseeding rates (V₁: low, V₂: medium, V₃: high) and three P levels (P₀: none, P₁: low, P₂: high) were established in this experiment. The factors were arranged in a completely randomized design, resulting in nine distinct treatment combinations, that is V₁P₀, V₁P₁, V₁P₂, V₂P₀, V₂P₁, V₂P₂, V₃P₀, V₃P₁, and V₃P₂. The results showed that the interaction between the reseeding and P addition exerts a significant effect on the biomass of M. ruthenica, forbs, and aboveground biomass (p < 0.05). Additionally, the interaction between the reseeding and P addition had a significant effect on crude protein content (p < 0.05). Phosphorus addition and the interaction between the reseeding and P addition had a significant effect on ether extract content (p < 0.05). However, it is only reseeding that can significantly influence the neutral detergent fiber content (p < 0.05). Grey correlation analysis revealed that the V₃P₂ treatment optimized both forage biomass and nutritional quality. Hierarchical partitioning further identified soil total nitrogen as the factor that contributed the most to forage biomass and quality following reseeding and phosphorus application.

Alfalfa (Medicago sativa L.), a drought-tolerant legume, significantly influences carbon and nitrogen cycling in arid and semi-arid regions. This study investigated carbon and nitrogen storage and sequestration dynamics in alfalfa pastureland cultivated for 2–7 years under temperate continental arid climate conditions (110–190 mm annual precipitation). Overall, the biomass, carbon and nitrogen sequestration in alfalfa pasture, and carbon and nitrogen storage and sequestration in soil exhibited a quadratic pattern with planting years. The above-ground biomass peaked at 19.28 t·hm⁻², with carbon and nitrogen sequestration reaching the highest level at 10.18 t·hm⁻² and 0.511 t·hm⁻², respectively, in year 5. Both annual carbon and nitrogen sequestration of the below-ground vegetation exhibited an increase, reaching a peak before decreasing with planting year, and from Y3 to Y7, the sequestration values were consistently higher than those in Y2. Soil carbon and nitrogen sequestration peaked in year 3. Compared to the adjacent fallow lands, alfalfa pasturelands maintained positive soil carbon sequestration until year 6 but became negative (−8.03 t·hm⁻²) by year 7. From years 2–6, alfalfa pasture fixed carbon and nitrogen at comparable rates but returned disproportionately less carbon than nitrogen to the soil. To optimize sustainability, we recommend (1) rotating alfalfa after 6 years to prevent soil nutrient depletion and (2) applying carbon-rich fertilizers post-year 3 to balance nutrients and prolong productivity in arid climates.