Effects of Companion Crops on the Production Performance and Nutritional Quality of Alfalfa in Desertified Saline–Alkali Soils of the Qaidam Basin

This study addresses the challenge of establishing alfalfa (Medicago sativa L.) in the desertified saline–alkali region of the Qaidam Basin, where seedling survival and productivity are considerably constrained. A two-year field experiment was conducted to identify suitable companion crops by comparing an alfalfa monoculture (control) with alfalfa intercropped with oat (Avena sativa L.) (O+A), forage pea (Pisum sativum L.) (P+A), or triticale (xTriticale Wittmack) (T+A). Agronomic traits, yield, and nutritional quality were measured, and a comprehensive evaluation was performed using the TOPSIS (Technique for Order Preference by Similarity to Ideal Solution) model. The results indicated that intercropping with oat produced the highest fresh and dry matter yields in the establishment year, while triticale and pea treatments exhibited strong yield potential in the subsequent year. Triticale significantly enhanced alfalfa’s nutritional quality by increasing crude protein content and relative feed value (RFV) while reducing fiber content. The TOPSIS model ranked the oat treatment highest for overall performance, effectively balancing yield and quality. In conclusion, oats are recommended as a companion crop to enhance alfalfa establishment in this saline–alkali environment, whereas triticale offers distinct advantages for improving the nutritional value of the forage.