2019 ASA Southern Regional Branch

February 03 - 05, 2019

Alfalfa (Medicago sativa L.) can enhance the supply of high-quality forage when interseeded into native warm-season grassland in the Southern High Plains (SHP). Alfalfa is a high water-using species; therefore, a possible trade-off between soil-water depletion and forage quality of the sward merits study. The objective was to determine the effect of interseeding alfalfa on crude protein (CP) and digestible organic matter (DOM) yield and to calculate the water footprint (WF, kg of evapotranspiration per kg of CP or DOM) of CP and DOM yields at two planting densities. Evapotranspiration was estimated as the difference between precipitation and the change in soil water storage in the root zone. Alfalfa presence reduced the WF (P < 0.001) with respect to CP and DOM yields by 56 and 30%, respectively, relative to control. The increased CP and DOM concentrations in forage mixtures compared to grass-only control (P < 0.0001) improved the WF. Hay-type alfalfa cultivars NuMex Bill Melton (NM) and WL 440HQ (WL) enhanced the forage mixture quality to a greater extent than grazing-type Falcata-Rhizoma (FR) blend, mainly driven by greater alfalfa DM production. Evidence of N transfer from alfalfa to companion grasses was observed through increased N content of the grass component in the mixture over grass-only control. Among cultivars, WL mixtures were more nutritious than NM and FR, attributed to its delayed maturity and high-quality trait. Managing alfalfa in wide rows (low planting density) in mixture with native warm-season grasses can increase the efficiency of water use (lower WF) by enhancing forage quality, thereby resulting in a minimal trade-off in soil water consumption.