Animal and Pasture Productivity of ‘Coastal’ and ‘Tifton 44’ Bermudagrass at Three Nitrogen Rates and Associated Soil Nitrogen Status

Abstract

electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher.T he productivity of grazing systems in the mid-Atlantic Region has been improved by the incorporation of the perennial warm-season (C 4 ) hybrid bermudagrasses (Gross et al., 1966;McLaren et al., 1983;Burns et al., 1984). Th e long-term productivity of bermudagrass, as measured by dry matter yield, depends on both N fertilization (Burton et al., 1963;Evers, 1985;Th om et al., 1990;Osborne et al., 1999, andJohnson et al., 2001) and defoliation frequency (Clapp et al., 1965;Ethredge et al., 1973). In grazing systems, the high yield potential of bermudagrass can only be realized through effi cient forage utilization. In a recent study on a Piedmont soil in the upper South with high N fertility (347 kg ha -1 ), Burns and Fisher (2008) compared steer daily gain and the productivity of Coastal and T44 bermudagrass at three herbage masses (HM). During the growing season, HM, when cut to the soil surface, was 2.36 Mg ha -1 for the short, 4.08 Mg ha -1 for the medium and 5.25 Mg ha -1 for the tall grazing treatments. Th ey reported least steer average daily gain (0.40 kg) from the short HM (2.36 Mg ha -1 ) and greatest (0.64 kg) from the medium HM (4.08 Mg ha -1 ) treatment. On the other hand, pasture productivity, as measured by eff ective feed units (EFU) or total digestible nutrients per unit area, was greatest (6.39 Mg ha -1 ) for the short HM and declined linearly being least (4.45 Mg ha -1 ) for the tall HM. Th e greatest EFU produced from the short HM refl ects a high degree of pasture utilization but sacrifi ced daily gain. Th eir data indicates that bermudagrass is well used when HM is maintained up to about 4.0 Mg ha -1 .Information for the Piedmont is not available on the response of bermudagrass to a range of N application rates managed at HM favorable to daily animal performance, and for eff ective forage utilization. Further, the movement of inorganic N in the soil profi le when applied generously to bermudagrass pastures has not been well assessed. Th e objectives of this experiment were to: (i) compare the daily animal response and pasture productivity of Coastal and T44 bermudagrasses over a range of N rates, (ii) determine N concentrations of the pasture canopy and of the animals' diet at increased N fertility, and (iii) determine the associated N (total and inorganic) status of the soil profi le aft er 3 yr of applying high rates of elemental N. MATERIALS AND METHODSTh e experiment was initiated in 2000 and conducted for 3 yr at the North Carolina Agricultural Research Service Reedy Creek Road Field Laboratory located in Raleigh, NC. Pastures (0.24 ha) were originally established in 1991 in a randomized complete block design with three pastures each of Coastal and T44 in two replicates. In the summer preceding this experiment the area was uniformly fertilized and the forage removed every 3 to 4 wk as hay. Th e pastures of each cultivar were rando...

Steer Performance and Pasture Productivity among Five Perennial Warm‐Season Grasses

“…In the Piedmont of North Carolina, steers grazing Tifton 44, compared with Coastal, gained weight at similar rates (0.55 kg d −1 ) at similar N fertility when stocked at 13.1 steers ha −1 (Burns and Fisher, 2008). When N rates varied (101–303 kg ha −1 ), the average daily gain (ADG) increased linearly for both cultivars but was greater for Tifton 44 (0.63 kg d −1 ) than Coastal (0.57 kg d −1 ; Burns et al, 2009). Although the stocking rate increased with increasing N rate, stocking rates were similar between cultivars, averaging 13 steers ha −1 .…”

Observations of High Nitrate Concentrations in Forage Bermudagrass during Severe to Exceptional Drought Years

“…Similarly, these model parameters were then used in Equation (6) to calculate the probability of HR [P(HR)] concentrations of NO 3 in the sample submissions for each growing season category.…”

“…Moreover, these observations indicate that NO 3 may accumulate in bermudagrass to a much higher level than previously thought. Of the published work that reports NO 3 concentration in forage bermudagrass [6]- [9], the highest reported level was 8350 mg NO 3 kg −1 [8]. The degree to which drought stress influences NO 3 concentrations in forage bermudagrass will need to be assessed in well-designed field trials.…”

“…Further, bermudagrass is highly efficient at using N and most of the nitrate reductase activity occurs in its roots [4]. Though this may reduce its risk in accumulating toxic concentrations of NO 3 [5], there is sufficient evidence to suggest that toxic NO 3 levels in bermudagrass do frequently occur [6]- [10]. However, it is unclear how frequent one might expect to find bermudagrass forage samples to be high in nitrates, especially during severe to exceptionally severe drought.…”

Effects of Applying Nitrogen on Yield of Introduced Perennial Summer Grass Cultivars in Oklahoma

“…Much research has been conducted examining differences among cultivars of these species (4,5,7,8,15), but under a single N rate. By contrast, much work has compared N fertilizer rates, but usually on a single variety (1,2,6,7,10,13,14).…”