Irrigated cool‐season grasses are needed in the Southern High Plains to extend grazing provided by winter wheat (Triticum aestivum L.) pasture and native range. Little information is available concerning their N requirements in relation to irrigation water application. The main objective of this study was to determine the N and water requirements for sustained high production of tall fescue (Festuca arundinacea Schreb.) and smooth bromegrass (Bromus inermis Leyss.). ‘Fawn’ tall fescue and ‘Southland’ smooth bromegrass were grown on Pullman clay loam (fine mixed thermic, Torrertic Paleustoll) under fertilizer N rates of 0, 168, 336, 504, and 672 kg ha‐1year‐1 on three water regimes. The N source was NH4NO3 except in a companion study in which feedlot manure was used. In one year of the 3‐year study when all irrigation treatments could be compared, adequately watered (W‐2) and fertilized (672 kg N/ha) tall fescue yielded 15.2 metric tons/ha, whereas similarly treated smooth bromegrass yielded 12.0 metric tons/ha. With moderate water (W‐I) and adequate N, however, smooth bromegrass yielded 6.9 and tall fescue yielded 5.2 metric tons/ha. With moderate water distributed for cool‐season forage production (W‐3), respective yields of similarly fertilized tall fescue and smooth bromegrass were 11.9 and 10.9 metric tons/ha. Also in 1976, first cuttings produced 77, 62, and 82% of total seasonal yields on W‐l, W‐2, and W‐3 plots, respectively. Over the 3‐year period, yield increases were almost directly proportional to the amount of N applied through 336 kg/ha. Yield increases per kg of applied N (to 336 kg/ha) were 12.1, 24.1, and 17.9 kg on W‐l, W‐2, and W‐3 plots, respectively. Feedlot waste, at N rates equivalent to those applied as‐ NH4NO3, was about one‐half as efficient as NH4NO3 in increasing yields. In the Southern High Plains, the most efficient irrigation management for tall fescue and smooth bromegrass is for early spring production with subsistence irrigation for the rest of the year.
Eleven grain sorghum (Sorghum bicolor L. Moench) hybrids were grown in the field and growth chamber. Leaf blade samples were assayed by in vitro and in vivo procedures for nitrate reductase activity (NRA) to i)termine NRA of the hybrids, ii) examine relationships between NRA and grain and N yields, and iii) determine whether NRA of growth chamber‐grown plants are indicative of those of field‐grown plants. Among hybrids, differences in yields of grain, dry matter, and grain protein and in in vitro NRA were significant though comparatively small. Seven hybrids had similar N input: accumulation ratios while four had lower ratios. This variation in N input:accumulation ratios, precludes the use of NRA, as assayed here, as a criterion for screening grain sorghum cultivars for N accumulation ability. Also, NRA values of young growth chamber‐grown plants were not indicative of those of field‐grown plants.
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 arundinacea Schreb.) and smooth bromegrass (Bromus inermis Leyss.) forage in the Southern High Plains. ‘Fawn’ tall fescue and ‘Southland’ smooth bromegrass were grown on Pullman clay 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 in 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 in irrigation. Although smooth bromegrass was superior to tall fescue in 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 in 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 in fertilizing for maximum production of high quality forage.
Yields of irrigated alfalfa (Medicago sativa L.) are lower on Pullman clay loam than on more permeable soils in the same climatic area. The objectives of this study were to determine (i) the residual effect of thoroughly mixing the soil profile on alfalfa growth and production, and (ii) the amounts and timing of irrigations required for maximum alfalfa production on modified and unmodified soil profiles.Alfalfa was grown under three profile modification treatments (thoroughly mixing the soil profile to 0‐, 90‐, or 150‐cm depth) on Pullman clay loam. For the first 3 years, all plots were either irrigated similarly (1970 and 1972) or unmodified plots were irrigated twice between harvests when necessary (1971). During the next 3 years, we expanded the study to include three irrigation treatments (two 10.2‐cm, one 17.8‐cm, or two 15.2‐cm irrigations between harvests). During the first 3 years, when single irrigations were applied between harvests, profile modification increased dry‐matter yields 40% (90‐cm modified) to 60% (150‐cm modified) over those for the unmodified check. However, with two irrigations between harvests, effects of modification were less marked.In the second phase of the study, with two 10.2‐cm irrigations between harvests, profile modification increased yields 30% (14.1 to 18.4 metric tons/ha). On 90‐cm modified soil, 3‐year average yields were 16.6, 18.3, and 20.1 metric tons/ha with one 17.8‐, two 10.2‐, or two 15.2‐cm irrigations between harvests, respectively. Respective yields on 150‐cm modified soil were 17.4, 18.5, and 18.6 metric tons/ha.Yields, water intake rates, bulk densities, and surface elevations showed that profile modification treatments made in 1964 were still effective 12 years later.
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