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Agronomy Journal Abstract -

Tall Fescue and Smooth Bromegrass. II. Effects of Nitrogen Fertilization and Irrigation Regimes on Quality1


This article in AJ

  1. Vol. 73 No. 3, p. 453-456

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  1. H. V. Eck,
  2. G. C. Wilson and
  3. Tito Martinez2



Both quantity and quality must be considered in selecting forages for livestock. This study was conducted to determine effects of N and irrigation treatments on the quality of tall fescue (Festuca arumtinacea Schreb.) and smooth bromegrass (Bromus inermis Leyss.) forage in the Southern High Plains. ‘Fawn’ tall fescue and ‘Southland’ smooth bromegrass were grown on Pullman day loam (fine, mixed thermic, Torrertic Paleustoll) under N rates of 0, 168, 336, 504, and 672 kg ha-1 year-1/ on three water regimes: W-l, a moderate (about 50-cm) and W-2, an adequate (about 100-cm) irrigation water level, both distributed for season-long production, and W-3, a moderate (about 60-cm) irrigation level distributed for cool-season forage production. Forage was harvested and analyzed for N, P, K, Ca, Mg, NO3- and in vitro dry matter disappearance (IVDMD). Nitrogen fertilization increased N, K, and NO3--N in both forages. The increased K levels increased the K/(Ca + Mg) ratios. Less marked effects of N included slight increases in IVDMD in both grasses, increases in Ca and Mg, and decreases in P in tall fescue but not in smooth bromegrass forage. The total N and NO3--N were lower and the Ca and Mg were higher to forage from W-2 than in that from W-l and W-3. With N rates through 336 kg/ha, NO3--N remained below the 2,000-ppm level considered harmful to livestock. Forage P and IVDMD were not affected by differences to irrigation. Although smooth bromegrass was superior to tall fescue to N, K, and Ca concentrations and in IVDMD, N fertilization at levels high enough to produce satisfactory yields increased the K/(Ca + Mg) ratios to levels considered critical for induction of grass tetany. With pure stands of smooth bromegrass, supplemental feeding of Mg would be necessary. Tall fescue contained more Mg than did smooth bromegrass, and its K/(Ca + Mg) ratios were favorable. Without P fertilization, feeding supplemental P would be necessary with both forages. Surface-applied feedlot waste, at N rates equivalent to those applied as NH4NO3, was less than one-half as efficient as NH4NO3 to increasing N to forage, but it increased P to levels satisfactory for nutrition of mature cows. Both irrigation adequacy and grass species must be considered to fertilizing for maximum production of high quality forage.

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