Forage potential of selected grasses in the southern high plains

On the southern High Plains, the supply of irrigation water from the Ogallala aquifer is decreasing, and pumping costs are increasing. Livestock production on forages can decrease water requirements and increase profitability. Forages that are productive and adapted to the climate of the southern High Plains are needed, and evaluation of these forages for production and nutritive value is important to the design of livestock grazing systems. Thus, 18 entries and advanced breeding lines of perennial cool-season grasses were evaluated for persistence, biomass production, and nutritive value under hay-cut or grazing management and limited (300 mm) irrigation over a 3 yr period. Grasses were established at the Texas Tech University Northeast Lubbock County Field Laboratory in small plots with four replications in a randomized block design. Hardinggrasses (Phalaris aquatica), tall fescues (Festuca arundinacea), smooth bromegrasses (Bromus inermis), tall wheatgrasses (Thinopyrum ponticum), and western wheatgrasses (Pascopyrum smithii) persisted well after 3 yr, whereas intermediate wheatgrass (Thinopyrum intermedium) stands declined. Biomass production averaged 6.5 Mg ha-1 (range 3.6 to 8.8 Mg ha-1) annually for all forages and was generally greatest for tall wheatgrass followed closely by hardinggrasses and Mediterranean tall fescues, and was least for smooth bromegrasses and intermediate wheatgrasses. Biomass production was generally greater in spring than autumn for wheatgrasses, but was greater in autumn than spring for tall fescues. Grazing steers selectively avoided tall wheatgrasses and western wheatgrasses until other forages were grazed. Forage nutritive value was generally greater for tall fescue, hardinggrass, and smooth bromegrass, and less for western wheatgrass and tall wheatgrass. Nutritive value was generally greater for grazed than non-grazed forage harvested as hay. Concentration of CP, ADF, and acid-insoluble lignin were more favorable in spring than autumn, but total nonstructural carbohydrate concentrations tended to be greater in autumn. ‘Jose’ tall wheatgrass may present a risk for grass tetany in spring with a K/(Ca + Mg) ratio (meq/meq) above 2.2. Mediterranean tall fescues exhibited low K/(Ca + Mg) ratios in spring suggesting below average risk for grass tetany. Copper and Zn were deficient in the plants for ruminant nutrition, but smooth bromegrass had greater Cu concentrations than other forages. Sodium concentration was sufficient in hardinggrass and tall wheatgrass to meet requirements for ruminants. Mineral concentrations often differed between Mediterranean and temperate fescues.

Ten species and entries of perennial warm-season grasses were established in a randomized block design with four replications to evaluate persistence, biomass production, and nutritive value under hay-cut management and limited irrigation. Sorghum almum (Sorghum almum), johnsongrass (Sorghum halipense), and kleingrass (Panicum coloratum) established the first year. Establishment required 2 yr for other grasses. Establishment was most difficult for eastern gamagrasses (Tripsacum dactyloides), big bluestem (Andropogon gerardii), and little bluestem (Schizachyrium scoparium). Most grasses persisted during the trial, but sorghum almum did not persist after 2 yr. Annual biomass production averaged 10.7 Mg ha-1 for all grasses (range 2.1 to 17.1 Mg ha-1). Annual biomass production was least for big bluestem, little bluestem, and sorghum almum, and differed little among other grasses. Kleingrass was generally greater in nutritive value than other grasses, whereas other grasses were similar.

Two forage-livestock grazing systems were evaluated for mineral concentrations in forage and mineral status of grazing steers. Mineral relationships between forage and the steers were examined. Trial 1 included pastures of ‘WW-B. Dahl’ (Bothriochloa bladhii), rye (Secale cereale) and wheat (Triticum aestivum). All forages were deficient in Ca, Cu, and Zn for ruminant nutrition, and ‘WW-B. Dahl’ also was deficient in S and P. Only Cu deficiency in the forage translated to a deficiency in the grazing steers, and a Mn deficiency also was detected in steer blood serum. Forage was adequate in Mn, thus, net Mn absorption seemed insufficient. Trial 2 consisted of a native grass mixture of blue grama (Bouteloua gracilis), buffalograss (Buchloe dactyloides), green sprangletop (Leptochloa dubia), and sideoats grama (Bouteloua curtipendula). The mixture was deficient in P, S, Cu, and Zn for ruminant nutrition. Serum minerals did not indicate deficiency but tended to decrease by the end of the grazing season. Greater K in blood serum of steers that had grazed ‘WW-B. Dahl’ than steers that grazed the native grass mixture correlated with greater K in ‘WW-B. Dahl’ than the native mixture. Greater S in blood serum of steers that had grazed the native pasture than steers that grazed ‘WW-B. Dahl’ was associated with greater forage S in the native mixture. Several species of warm- and cool-season perennial grasses were identified that show promise for forage production on the southern High Plains with limited irrigation. Characteristics of the grasses that include persistence, biomass production, and nutritive value were determined that will help producers make informed decisions when incorporating these grasses into the design of their grazing system.