Effects of mixed seeding ratio on biomass allocation and competition of Onobrychis viciifolia and Elymus nutans under cold conditions in the Tianzhu alpine region

Mixed seeding is an important method for establishing grassland in cold alpine regions. In this study, a field experiment using Onobrychis viciifolia and Elymus nutans mixed in different ratios (100∶0, 70∶30, 50∶50, 30∶70, and 0∶100) was conducted from 2018−2019 in Tianzhu County to explore growth dynamics and inter-species competition. The results showed that the biomass of mixed communities reached a maximum at the end of the first growing season. The land equivalent ratio (LER) was relatively high and the aboveground biomass was larger (3 172.2 kg·ha⁻¹) when the ratio of O. viciifolia to E. nutans was 70∶30. Competition between O. viciifolia and E. nutans was weak the competitive ratio (CR) was close to 1 and the actual yield loss (AYL) of the community was close to, or less than 0. During the second year, the CR and aggressivity (A) of O. viciifolia was higher than that of E. nutans because the absolute and natural heights were low in June. As community growth continued, the absolute and natural heights changed consistently so that the growth space tended to be filled. The competitive strength of O. viciifolia (CR, A) was different from that of E. nutans during this stage. The range of LER was 1.33～1.68 and the AYL was 24.0%～57.0%. The biomass of the 30∶70 ratio was 9 178.8 kg·ha⁻¹ and was the highest of all the treatments, being equivalent to 3.6 times that of O. viciifolia and 1.6 times that of E. nutans when grown alone. The mixed grassland with different ratios of O. viciifolia and E. nutans performed differently at different growth stages. The total biomass of the two growth seasons was highest when the planting ratio was 30∶70. The ratio of mixing for grassland seeding should be adopted based on demand.