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Title: Eastern Gamagrass Management for Pastures in the Mid-Atlantic Region: II. Diet and Canopy Characteristics and Stand Persistence

item Burns, Joseph
item FISHER, DWIGHT - US Department Of Agriculture (USDA)

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/10/2009
Publication Date: 1/25/2010
Citation: Burns, J.C., Fisher, D.S. 2010. Eastern Gamagrass Management for Pastures in the Mid-Atlantic Region: II. Diet and Canopy Characteristics and Stand Persistence. Agronomy Journal. 102:179-186

Interpretive Summary: Eastern gamagrass, when established in narrow rows (15 cm), provided adequate ground cover for utilization as pasture. Pastures were successfully grazed using both continuous and rotational stocking. Pasture of EG were predominately green leaf (78.2%), regardless of stocking management. The bunch-type growth habit of EG, however, prevents development of a dense sward. Consequently, leaf management of EG pastures is an important aspect of achieving desirable steer performance, maintaining pasture productivity and ensuring stand survival. Maintaining an average pasture height of 38 cm, or a mean forage mass (FM , 10-cm stubble) of about 1100 kg ha-1 was associated with steer gains of 0.90 kg d-1 and was superior to gains of 0.57 kg d-1 from well managed, continuously stocked Coastal bermudagrass. To retain reasonable longevity of EG stands, pastures should not be continuously defoliated below about 20 cm. The longevity of EG pasture stands can be extended by less intense defoliation, however, steer daily gains will likely decline because of the open canopy characteristics and animal grazing behavior. Total and digestible leaf mass dominated the canopy with a linear (P < 0.01) increase with increasing FM (278 to 1393 kg ha-1 and 194 to 922 kg ha-1). The two rotational treatments had similar proportions of leaf, stem, head, and dead fractions and were of similar nutritive value. The diet selected from the continuously stocked treatments were similar in IVTOD (751 g kg-1), CP (151 g kg-1) and NDF (654 g kg-1) whereas the diet selected from the rotational treatment differed (P = 0.05) being greater in IVTOD (791 g kg-1) and least in NDF (624 g kg-1). Eastern gamagrass stands declined from being initially similar (60.3% basal cover) among all treatments to 29.8 % basal cover after 4 yr of grazing. Stands declined linearly (P = 0.09) with decreasing FM (34.5 % for Tall vs. 11.5% basal cover for Short) and rotationally stocked pastures were similar to the Tall treatment (35.5% basal cover). Eastern gamagrass pasture, if stocked continuously, should be grazed at about 38 cm to obtain desirable steer ADG and retain acceptable stand longevity. Rotationally stocking of the pastures may prolong stand longevity with a small sacrifice in steer ADG.

Technical Abstract: Eastern gamagrass [Tripsacum dactyloides (L.) L.], a native warm-season perennial grass, lacks evaluation for use in grazing systems. Our objective was to test eastern gamagrass (EG) in a 4-yr experiment to estimate forage mass (FM) that maximizes steer performance and pasture productivity. Pasture canopy characteristics, diet selection by grazing steers, and stand persistence from EG continuously grazed at Short, Medium, and Tall heights and two rotationally stocked treatments were compared with continuously stocked ‘Coastal’ bermudagrass [Cynodon dactylon (L.) Pers.]. The EG had proportionally more green leaf (78.2 vs. 24.5%), less stem (4.4 vs. 45.2%), less heads (0.4 vs. 5.6%) and similar dead tissue (17.0 vs. 24.8%). Plant fractions were similar in proportion among EG treatments. Digestible leaf mass was greater in EG than in bermudagrass (P < 0.01; 713 vs. 292 kg ha-1) and dominated the EG canopies with a linear (P < 0.01) increase in leaf mass with increasing FM (194 to 922 kg ha-1). Diets were similar in IVTOD (738 g kg-1), CP (151 g kg-1), and NDF (654 g kg-1) when continuously stocked but greater (P < 0.01) in IVTOD (791 g kg-1), and least in NDF (624 g kg-1) from the rotation. Stand declined linearly (P = 0.09) with decreasing FM (Tall = 34.5 and Short = 11.7% basal cover) but was similar between the two rotational systems (35.5%). Continuously stocking EG at about 38 cm gave greatest steer daily gain but rotations may prevent declines in stands with some sacrifice in gains.