Interseeding alfalfa into native grassland for enhanced yield and water use efficiency

Livestock productivity of semiarid, native grassland is potentially enhanced by interseeding alfalfa (Medicago sativa L.), but little is known of the impact on forage and N yield and water use. Two hay-type cultivars, ‘WL 440HQ’ (WL), ‘NuMex Bill Melton’ (NuMex), and grazing-type ‘Falcata’–‘Rhizoma’ blend (FR) were interseeded into mixtures of four native-grass species in fall of 2015, at 36- and 71-cm row spacing as high- and low-density plantings, respectively. Plots were harvested periodically over 3 yr. Evapotranspiration (ET) was estimated based on rainfall and changes in soil water volume and used to calculate water use efficiency (WUE, kg of forage mass m⁻³ of ET). Alfalfa–grass mixtures produced 35% more forage mass and 96% greater N yield than the grass-only stands. Narrow-row alfalfa produced greater total forage mass than wide-row for the first 2 yr (P <.05), but no difference between row spacings occurred by Year 3. Cultivars NuMex and WL produced greater forage mass than the short-statured FR, especially at high density (P <.05). Alfalfa–grass mixtures increased WUE by a mean of 25% over the grass-only stands. There was no difference between row spacings for WUE, weed biomass, and weed N mass (P >.05). The alfalfa–grass mixtures reduced weed biomass by 43% over the grass-only stands. Interseeding alfalfa at wide row spacing enhanced forage productivity, WUE, and weed suppression relative to grass-only stands at lower seed cost than at narrow row spacing. Adapted hay-type alfalfa cultivars can be used to improve native-grass pastures in rainfed, semiarid environments.