Response of three warm-season grasses to varying fertility levels on five soils

Animal production in New England has been limited by inadequate forage during mid- to late summer when cool-season grasses are in summer dormancy. Big bluestem (Andropogon gerardi Vitman), indiangrass [Sorghastrum nutans (L.) Nash] and switchgrass (Panicum virgatum L.) are warm-season grasses that may be a perennial source of summer forage. Since production of these warm-season grasses would be limited to the less fertile soils of the region, a greenhouse study was conducted to examine the growth and quality of these species in five acid, infertile soils as well as fertilizer-amended soils. The soils were fertilized with limestone (L), limestone plus nitrogen (LN), limestone, nitrogen plus phosphorus (LNP), and limestone, nitrogen, phosphorus plus potassium (LNPK). Limestone was applied to adjust soils to a pH of 6.5. Fertilizer was applied at rates of 45, 117 and 111 kg/ha of N, P and K, respectively. First harvest yields were greatest for switchgrass and big bluestem, but indiangrass produced significantly greater yields than either of the other grasses in the second harvest. In both harvests, the yields of all grasses were greatest under the LNP and LNPK fertility regimes. Nitrogen, without P, did not significantly increase yields above the control treatment in the first harvest. Yield responses to P fertilization varied with soils. Although P appeared to be the limiting factor insofar as growth was concerned, the yield response from P fertilization would probably be limited without N fertilization. Indiangrass was significantly higher in crude protein and K concentration and significantly lower in Ca concentration than big bluestem and switchgrass. Phosphorus concentrations were below the recommended levels for ruminant nutrition.