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Time and Rate of Fertilizer Application for Seeded Warm-season and Bluegrass Pastures. I. Yield and Botanical Composition¹

Field studies were initiated in 1971 and continued through 1974 to evaluate the influence of time and rate of fertilizer application for both seeded warm-season and bluegrass (Poa pratensis L.) pastures. The warm-season pastures consisted of a mixture of big bluestem (Andropogon gerardi Vitman), switchgrass (Panicum virgatum L.), indiangrass (Sorghastrum nutans L.) and sideoats grama (Bouteloua curtipendula L.). Prior studies had shown that fertilization would increase production of several forage species. Yet results were often conflicting and influence of time of fertilizer application had not been investigated. Rates of fertilization ranged from O to 180 kg N/ha and from O to 34 kg P/ha. Fertilizer was broadcast in both early and late spring on established stands on Crofton silt loam, a Typic Usthorthert. Applications were repeated each year. The relationship between yields of the bluegrass to rate of applied N and P was linear in each year of the study. Higher yields were recorded when fertilizer was applied in early (15 April) compared to late (30 May) spring.

For the warm-season grasses, the relationship of yields to rate of N application was linear in 1971 and 1972 but was curvilinear in 1973 and 1974. Yields were linearly related to rate of P applied in all years except 1972. Botanical composition of the warm-season grass mixture was influenced by time of fertilization. Early spring application encouraged encroachment by cool-season species, intermediate wheatgrass (Agropyron intermedium Host.), which dominated the stand after 2 years of fertilization. Application of N rates less than 90 kg/ha in late spring did not result in encroachment. At the lower N rates, higher yields of warm-season grasses were observed when fertilizer was applied in late spring.

Key Words: Grass Fertilization • Botanical Composition • Warm-Season Prairie Grasses

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

Received for publication February 11, 1976.