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Title: Steer Performance and Pasture Productivity of Caucasian Bluestem at Three Forage Masses

item Burns, Joseph
item Fisher, Dwight

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/20/2010
Publication Date: 4/20/2010
Citation: Burns, J.C., Fisher, D.S. 2010. Steer Performance and Pasture Productivity of Caucasian Bluestem at Three Forage Masses. Agronomy Journal. 102:834-842.

Interpretive Summary: Caucasian bluestem stands were readily established and pastures effectively utilized by steers. Canopy heights of about 14, 32 and 40 cm resulted in forage mass (FM) levels of 1.42, 2.31 and 2.75 Mg ha-1 and resulted in similar steer ADG (mean = 0.76 kg) when continuously stocked. Pasture at the Short canopy height, however, produced greatest weight gains ha-1 averaging 817 kg ha-1 when stocked at 9.7 steer ha-1. Pastures grazed at the 32 and 40 cm mean canopy heights were stocked with fewer cattle (7.8 and 7.0 head ha-1, respectively) to maintain the FM and produced less gain ha-1. Pasture productivity (calculated as effective feed units) was greatest for Short FM averaging 4,025 kg ha-1 and declined linearly to 2806 kg ha-1 for the Tall FM. Masticate data indicated that steers were able to select a diet that was greater in IVTOD (761 g kg-1) and CP (110 g kg-1) than the mean of the offered canopies (IVTOD = 638 and CP = 80 g kg-1), but less than the leaf fraction alone (IVTOD = 832 and CP = 116 g kg-1). Further, the differential between selected diet and diet on offer increased with increasing FM. The similarity of ADG among the canopy heights is attributed to a lack of FM and subsequently dry matter intake at the shortest canopy height. Ground cover, representing stand persistence, was greatest at 70% for the Short FM and declined linearly to 22.8% for the Tall FM. Consequently, close continuous defoliation was beneficial and would be an objective in production systems. Caucasian bluestem has potential as a warm-season pasture for the mid-Atlantic Region. Its productivity, however, is limited mainly to mid-May through mid-September. Although this period interfaces well with the general growth curve for adapted cool-season perennial grasses, the land devoted to Caucasian bluestem will be non-productive for much of the year. The interseeding of Caucasian bluestem in the fall with a cool-season annual for either a harvested forage (removed in late March) or grazing in late winter may have merit in a production system.

Technical Abstract: The introduced perennial, warm-season grass, Caucasian bluestem [Bothriochloa caucasia (Trin.) C.E. Hubbard ‘Caucasian’], appears to be adapted to the Mid-Atlantic region. This 4-yr experiment compared animal and pasture productivity of Caucasian bluestem over three canopy heights designated as Short (14.6 cm), Medium (32.2 cm) and Tall (39.8 cm). The relationship of canopy height to diet and canopy characteristics was also evaluated. The soil was a Cecil clay loam (fine, kaolinitic, thermic Typic Kanhapludult). Pastures were continuously stocked using variable stocking and grazed from mid May through mid September. Forage mass (FM) (harvested to a 2.5-cm stubble), increased linearly (P = 0.04) averaging 1.42, 2.31 and 2.75 Mg ha-1 for the Short, Medium and Tall canopy heights. Steer average daily gain was similar among FM treatments (0.76 kg) but weight gain decreased linearly (P < 0.01) from Short to Tall (from 817 to 518 kg ha-1). Increasing FM was associated with a quadratic decrease (P = 0.04) in stocking rate (from 9.7 to 7.8 steers ha-1) and animal days (from 1019 to 700 day ha-1) and a linear decrease (P = 0.02) in effective feed units (from 4025 to 2806 kg ha-1). Stand counts increased linearly (P = 0.05) from the Tall to the Short FM (from 22.8 to 70.0%) with the Tall providing openings for potential weed invasion. Caucasian bluestem is a warm-season grass that can be heavily stocked and provide good quality forage for summer grazing in the mid-Atlantic region.