Ontogenesis and nutritive value of warm-season perennial bunch grasses

Understanding the dynamics of nutritive values in warm-season perennial bunch grasses with change in ontogenesis is essential to managing their use as forage for livestock or cellulosic bioenergy feedstock. Accumulated growth (not previously harvested) of Alamo lowland and accession 9065018 upland switch grass ( Panicum virgatum ), Lometa Indian grass ( Sorghastrum nutans ), Earl big bluestem ( Andropogon gerardii ), San Marcos eastern gama grass ( Tripsacum dactyloides ) and Haskell sideoats grama ( Bouteloua curtipendula ), all native to the southern Great Plains of North America, as well as Selection 75 Klein grass ( Panicum coloratum ), originating in southern Africa but selected in North America, was harvested every 28 d for 3 yr, commencing 1 yr after establishment. Growth stage, crude protein (CP) and in vitro dry matter disappearance (IVDMD) over 48 h were evaluated at each date. Some entries, such as Haskell, San Marcos and Selection 75, initiated reproductive growth earlier in the growing season and had higher nutritive value [up to 119 g CP/kg dry matter (DM) and 630 g IVDMD/kg DM] at seed set than those reproducing later in the season. Nutritive value of San Marcos and Selection 75 responded to autumn rainfall with resurging nutritive value (over 100 g CP/kg DM and over 600 g IVDMD/kg DM), whereas others did not. These nuances in nutritive value may be useful in manipulating species composition and season of utilization for grazing bunch grasses, especially when incorporated into opportunistic harvests of bioenergy feedstock.