Effects of monoculture and mixed sowing with different densities on growth characteristics and interspecific competition of Leymus chinensis and Medicago sativa

In this study, a controlled pot experiment was conducted to measure and analyze changes in growth characteristics, productivity, and competitive relationships between Leymus chinensis and Medicago sativa under different sowing methods (monoculture and mixed sowing) and densities (normal and high). The results showed that: 1) time had a highly significant effect on the plant height and growth rate of both forages (P < 0.001). The sowing method had a significant effect on the plant height growth rate and dry to fresh ratio of L. chinensis (P < 0.05), and sowing density significantly affected its plant height (P < 0.05). The sowing method and density significantly affected the plant height, growth rate, and dry to fresh ratio of M. sativa (P < 0.05). All three factors(time, sowing method, and sowing density) had a significant interaction with the plant height and growth rate of M. sativa (P < 0.05). 2) L. chinensis and M. sativa had higher plant heights under high density monoculture and high density mixed sowing, respectively, with higher growth rates at greening and harvest for L. chinensis and at tillering and harvest for M. sativa. The dry to fresh ratio of L. chinensis was higher under monoculture sowing, and that of M. sativa was significantly higher than under mixed sowing only under normal density monoculture sowing. The aboveground biomass of normal and high-density mixed sowing was 5.02% and 8.79% lower than that of monoculture sowing, respectively. 3) The interspecific compatibility between the above-ground parts of the two forage grasses was good under different density mixed sowing treatments, and the competition between the below-ground species intensified with increasing density. The competitiveness of L. chinensis was higher than that of M. sativa under different densities of mixed sowing, but it decreased with the increase of density. The results showed that monoculture sowing of L. chinensis and M. sativa was conducive to the accumulation of forage biomass, and mixed sowing was conducive to the reduction of the stem to leaf, root to shoot, and dry to fresh ratios of forages.