Ona Report… (Continued from page 12)
heights. In addition, bahiagrass is resilient to frequent harvests because it has a significant proportion of the total mass (approximately 50%) allocated to reserve structures (roots and rhizomes) below ground. Those structures allow the plant to regrow, even with little leaf area remainingaftergrazingorharvest. When increasing N fertilization
is not an economic option, rotational grazing may enhance the productivity of bahiagrass pastures. Research conducted at the Range Cattle Research and Education Center, Ona, FL compared two grazing frequencies on four bahiagrass cultivars. Pensacola, Argentine, Tifton 9, and Riata plots were fertilized with 60 lb N/acre in the spring and grazed at 2 or 4 weeks intervals during 2010. Cows grazed the plots for approximately12hoursandwere removedwhenthestubbleheight reached 3 inches. Cows were returnedtoplotsafter2or4weeks of rest to simulate two rotational grazing frequencies. Tifton 9 and Riata plants were taller and had a slight greater herbage mass than Pensacola and Argentine during the growing season. In the fall, none of the cultivars produced enough forage to be grazed at 2 weeks intervals. The dry and early cold weather experienced in the fall 2010 limitedherbagemassproduction
ofallcultivars.Althoughtherewas onlyaslightdifferenceinherbage
a c c u m u l a t i o n among cul t ivars, grazing frequency significantly affected production. Plots grazed at 4 weeks had 30% greater forage production (Table 2) than those grazedevery2weeks. Sunlight is the major source of energy for photosynthesis and herbage production. Warm-seasongrasses reach the optimum production when the leaves are able to intercept approximately 95%of
thesunlight.Thebahiagrass plots grazed at 4 weeks were able to intercept 91% of the sunlight. Plots grazed at 2 weeks onlyintercepted64%. Inaddition, the plots grazed at 2 weeks had fewer tillers than plots grazed at 4 weeks intervals,whichcouldresult in fewer plants per area and an opportunity for weeds. No stand decreaseswereobservedduring the first year of the research; however, thedecreaseinnumber of tillers may be an indication of poor persistence and future stand decline. Tifton 9 and Riata had more upright growth and were more sensitive to frequent andintense harvest afterathree- year study in Gainesville. Bottom line, bahiagrass production can be improved by allowing longer
restingperiods.Thus, it isbeneficial to rotate the animals, even if they are in an extensive grazing system with low N fertilization levels. It is unlikely that the 30%
increase in forage production wouldincreasetheaveragedaily gain of the animals; however, it will likelyallowincreasedstocking ratesandimprove gain per acre. Ingeneral,1.0to1.5lbof forage
(dry matter) perpoundof animal liveweightexposedtothepasture provides adequate forage for cow-calf pairs. For example, considering that 1.5 kg DM / kg liveweight is recommended, if the pastureisgrazedcontinuouslyand has 1,000 lb forage DM, it would be necessary approximately 1.5 acres to provide sufficient forage for a 1500 lb cow-calf pair. The same pasture, if grazed rotationally, could potentially have 1,300 lb DM, and only 1.15 acres would be necessary to support the same cow-calf pair during the growing season. The extra forage produced could also be excluded from grazing andharvestedashayorhaylage. If you have any questions on
bahiagrassgrazingmanagement, please contact Joe Vendramini,
jv@ufl.edu.
Table 1. herbage mass and nutritive value of warm-season grasses harvested in the summer. Item
HM,lb/acre 13,050 CP, %
9.6
ADF, % NDF, %
45.2 68.6
Digestibilty % 59.1
2600 12.9 37.3 63.6 56.3
Height 6 11
3670 12.0 40.5 71.7 61.7
L1
320 12.6 39.1 63.2 67.0
3870 12.5 36.3 65.7 60.1
Herbage Mass 4 14 / THE FLORIDA CATTLEMAN / MAY 2011
1200 1600
4600 11.6 40.5 72.2 58.4
Tiller Density 850 1103
3090 12.9 37.8 67.5 63.2
Elephantgrass Bahiagrass Stargrass Mulato Limpograss Jiggs Coastcross 2 Tifton Florakirk 85
2970 10.2 27.0 58.0 63.9
Frequency
(weeks) 2
(Inches) (%)
64 91
(b DM/acres) (perfilhos/sq meter)
Digestibility (%)
54 51
3800 11.6 40.1 71.4 58.0
Table 2. Grazing frequency effects on forage production and nutritive value of four bahiagrass cultivars. Grazing
CP (%)
10 13
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