Effect of mixed sowing of graminaceous and leguminous forages under different water regimes in Ningxia central semi-arid belt

Two leguminous forages (Medicago sativa and Astragalus adsurgens) and three graminaceous forages (Bromus inermis, Elymus dahuricus, and Agropyron cristatum) were sown separately and in six combinations in Ningxia central semi-arid belt under three water treatments, i.e. low irrigation (484 mm), intermediate irrigation (707 mm), and high irrigation (1 160 mm). Yield, the whole plant Δ13C, and photosynthetic exchange parameters were determined. The results showed that mixed sowing of graminaceous and leguminous forages could improve yield and water use efficiency (WUE) in central Ningxia when irrigated. Among the different combinations that were sowed, the highest Δ13C, yield, and WUE were recorded when Astragalus adsurgens was combined with Elymus dahuricus. There was a significant effect of water treatment on the plant height, photosynthetic physiological parameters, yield, and Δ13C of graminaceous and leguminous forages (P<0.05). The values of yield, WUE, and Δ13C were the highest in high irrigation treatmentand the lowest in low irrigation treatment. Yield and WUE were found to correlate significantly with Δ13C, leaf stomatal conductance (Gs), leaf temperature, and plant height in high irrigation treatment and in low irrigation treatment. The former can be used as an alternative selection indicator for screening high-yield combinations and the latter can be used as an alternative selection indicator for screening water-saving combinations.