Morphological characteristics of water stress in mixed or unicast seeding of Vicia sativa and Secale cereal in Tibet

In this study, the effects of different degrees of water stress on mixed or unicast forage grasses were simulated by using annual grazing peas and green wheatgrass, and the responses of morphological characteristics to water stress were preliminarily investigated. The results showed that after 16 days of water stress, the soil moisture content of a pea (Vicia sativa) unicast was significantly higher than those of other mixed treatments and rye (Secale cereal) unicast (P < 0.05). Water stress affected the growth and development of forage grass, inhibited the leaf length and width of pea, and inhibited the leaf width of rye, but had little effect on the leaf length of rye. Additionally, water stress promoted root elongation. The root length of peas reached a maximum at 20 days after water stress (part of the treatment was the end of stage stress when drought causes plant death), and the root length of unicast pea was the longest (37.83 cm). The change in root length in rye was similar to that in pea. The root length of rye in JL1 (pea 25% + rye 75%) was 60.5 cm, which was significantly higher than those after other mixed treatments (P < 0.05). The drought resistance coefficient of the plant height and leaf length width was less than 1, and the root drought resistance coefficient was greater than 1, which inhibits plant growth aboveground, while the elongation and growth of underground roots were promoted. In this study, comprehensive evaluation of the drought resistance of pea and rye by the membership function method showed that the unicast pea has the strongest drought resistance, and the 3 proportionally mixed sowing designs exhibited no obvious drought resistance advantage when compared with the unicast.