Grassland production performance and photosynthetic characteristics under different alfalfa densities and grass bean mixed sowing

A grassland was established by interrow (A₁) and cross-row (A₂) seeding of alfalfa (Medicago sativa) and brome (Bromus inermis) with eight different alfalfa population densities (5, 15, 25, 35, 45, 55, 65, and 75 seeds·m⁻², denoted as B₁, B₂, B₃, B₄, B₅, B₆, B₇, and B₈, respectively). The annual and individual stubble yields and the growth and photosynthetic characteristics of the first stubble grass were measured to study the effect of the mixed planting method and alfalfa population density on forage yield, growth characteristics, and photosynthetic characteristics. The results showed that the yield, growth characteristics, water use efficiency, chlorophyll content, and carotenoid content of cross-sown grass were significantly higher than those of inter-row mixed sowing (P < 0.05). Conductivity, intercellular CO₂ concentration, and transpiration rate were significantly higher than those of the cross-row seeding (P < 0.01). The annual grass yields of B₁ and B₃ were significantly higher than those of B₄～B₈ (P < 0.01), and the annual yields of alfalfa and grass-bean in B₆ was significantly higher than those of B₁, B₂, and B₃ (P < 0.01). The B₃ treatment resulted in the highest photosynthetic rate, stomatal conductance, and transpiration rate. In summary, the stability of cross-sown alfalfa at 15～25 seeds·m⁻² in the brome grassland in Horqin Sandy Land was good, and the total yield of peas was high in the inter-row mixed-sowing with 45～55 alfalfa seeds·m⁻².