|Wagger, Michael - NORTH CAROLINA STATE UNI|
Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 17, 2008
Publication Date: January 15, 2009
Citation: Burns, J.C., Fisher, D.S., Wagger, M.G. 2009. Animal and Pasture Production of 'Coastal'and 'Tifton 44' bermudagrass at three nitrogen rates. Agronomy Journal. 101:32-40. Interpretive Summary: This study provides a timely assessment of the response of bermudagrass to increasing N application rates when utilized as pasture. Bermudagrass responds to N in both nutritive value concentration and in dry matter production. The per animal and per hectare productivity was addressed for both Coastal and Tifton 44 bermudagrass, both adapted and grown across the mid-Atlantic Area. Further, assessment was made of the nature of the pasture canopy offered in terms of morphological (leaf, stem, and dead) characteristics, the diet selected by the grazing animal and it nutritive value relative to the pasture on-offer. Finally the soil was characterized for pH, inorganic and total N, and for its carbon status. Tifton 44 was of greater nutritive value than Coastal, as reflected in greater steer average daily gain. Coastal and Tifton 44 had similar productivity under grazing and N application had a major impact on increasing stocking rate and consequently animal and pasture productivity. Soil inorganic N was well below the safe guidelines for drinking water at the highest N rate evaluated. These data provide a guide on which to assess the recent high cost of N weighed against the added pasture productivity relative to the value of the harvested beef.
Technical Abstract: Nitrogen fertilizer is an important input for bermudagrass [Cynodon dactylon (L.) Pers.] production across the Southeastern USA but return in the quality and quantity of pasture produced for fertilizer invested must be carefully tested. This 3-yr experiment compared grazing animal performance and pasture productivity of ‘Coastal’ and Tifton 44’ Bermudagrass with three annual nitrogen application rates of 101, 202 and 303 kg of N ha-1 on a Cecil clay loam soil. Characteristics of the ingested forage were also evaluated. Herbage mass (to soil surface) differed for Coastal and Tifton 44 (T44) (26.1 and 23.4 Mg ha-1;P < 0.01) but was similar among N rates. Steer average daily gain was greater for T44 (0.63 kg d-1 vs. 0.57 kg d-1; P < 0.01) and increased (P = 0.05) with increased N application. Cultivars were similar in weight gain ha-1 (884 kg) and in effective feed units (EFU) (4735 kg ha-1) but weight gain per hectare and EFU increased with N application. Soil inorganic N was similar between Coastal and T44 plots (mean = 7.9 mg L-1). After 3 yr of grazing a N rate by soil depth interaction occurred for inorganic N, with the greatest concentration at 0-15 cm (11.1 mg L-1) for the 101 N rate but at the 30-60 cm depth (14.7 mg L-1) for the 303 N rate. Both bermudagrass cultivars and steers responded to the 303 N rate. Residual soil inorganic N concentrations were well below ground water standards.