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Time and Rate of Fertilization on Seeded Warm-Season and Bluegrass Pastures. II. Quality and Nutrient Content¹

There is relatively limited available information to be found which pertains to the effect of fertilizer application on the quality and nutrient concentration of seeded warm-season as well as bluegrass pastures grown under more arid conditions. Therefore, this study was designed to measure the influence of the application of N and P fertilizers in early (mid-April) and late (late May) spring on the quality (protein and in vitro dry matter disappearance) and nutrient (NO₈^–-N, P, K, Ca, Mg) concentration of seeded warm-season and bluegrass (Poa pratensis L.) pastures from 1971 through 1974. Applications of N (0, 45, 90, 135, and 180 kg/ha) and P (0, 8.5, 17, 25.5 and 34 kg/ha) were repeated in each of the 4 years. Whole-plant samples were collected from each plot at harvest. These samples were analyzed for in vitro dry matter disappearance (IVDMD) and protein percentage. In addition, whole-plant samples were collected from all plots approximately 30 days after fertilizer application in both 1973 and 1974. These samples were analyzed for NO₃-N, protein-N, P, K, Ca, and Mg.

Fertilization with both N and P had no consistent effect on the IVDMD percentage of mature forage. The protein percentage of the mature forage increased linearly with rate of fertilizer N. Kentucky bluegrass forage had a higher percentage of protein than the mixture of warm season prairie grasses which consisted of big bluestem (Andropogon gerardi Vitman.), switchgrass (Panicum virgatum L.), indiangrass (Sorghastrum nutans (L.) Nash.), and sideoats grama (Bouteloua curtipendula (Michx.) Tarr.). Protein production from the bluegrass pasture was increased eight-fold by application of both N and P. There was a six-fold increase in protein production from the warm-season prairie grasses when adequate rates of both N and P were applied. The concentration of P in samples collected at harvest as well as those collected 30 days after fertilizer application increased linearly with rate of applied P in all cases.

The ratio,
, exceeded the critical value of 2.2 only when N and P were applied to the warm season grasses in early spring of 1974. The concentration of NO₃^–-N in forage from both pastures was increased by applied N but did not approach the 2,000 ppm level generally considered to be lethal to livestock.

Key Words: Fertilization • Warm-season grasses • Forage quality • Tetany ratio • Nitrate in forage

² Associate professor. Northeast Station, Univ. of Nebraska, Concord, Neb. and professors. Univ. of Nebraska, Lincoln, respectively.

Received for publication May 26, 1976.

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