Effects of Qingtian No.1 and Leguminosae forage mixed sowing on soil physical and chemical properties and forage growth and development in high-altitude areas

To identify the optimal combination and proportion for mixed sowing of Avena sativa and leguminous forage in high-altitude areas (above 4 000 m), we conducted mixed sowing of the A. sativa variety Qingtian No.1 with common Vicia sativa, Pisum sativum, and Vicia faba. We evaluated the production performance, nutritional quality, and soil nutrients in plots treated with different mixed-sowing combinations and proportions of forage. The results revealed that the height of Qingtian No.1 plants was tallest under the B3 treatment (Qingtian No.1, 135.0 kg·hm⁻²; Vicia faba, 30.0 kg·hm⁻²). Regarding leaf-related traits, treatment B6 (Qingtian No.1, 157.5 kg·hm⁻²; Pisum sativum, 22.5 kg·hm⁻²) was superior to other mixed-sowing treatments. Treatment B6 also produced the highest hay yield (8 880 kg hm⁻²), significantly surpassing other treatments (P < 0.05), with an increase of 64.44% compared with unicast Qingtian No.1 (A1). Additionally, the forage quality of each of the mixed-sowing treatments was superior to that of unicast A1, among which, the crude protein and crude fat contents obtained using treatment B6, with contents of 16.10% and 7.18%, respectively, which were significantly higher than those obtained using the other mixed-sowing treatments. The enzyme activity in soil receiving the mixed-sowing treatments was significantly higher than that of each single-sowing treatment, and the soil nutrient content was relatively balanced, with most of the assessed indices being significantly higher than those measured in soil with single-sowing A1; however, there were no significant differences between the mixed-sowing treatments and single sowing of leguminous forage. A comprehensive evaluation of membership function showed that the value of the membership function of treatment B6 (0.772) was the highest, and at Grade I considered excellent. In conclusion, the indices showed that the treatment B6 ,(Qingtian No.1, 157.5 kg·hm⁻²; Pisum sativum, 22.5 kg·hm⁻²), in each unicast and mixed-sowing treatment outperformed other treatments, and these mixed-sowing treatments are recommended for the use in in high-altitude areas (above 4 000 m).