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Increasing Bahiagrass Production in Low-Input Grazing Systems

May, 2011
by Joao Vendrmaini, UF/IFAS, Range Cattle REC, Ona

Warm-season grasses are the predominant forages for cow-calf operations in Florida. While warm-season grasses are more productive than most other forage plants, they require N fertilization to achieve their full potential production. Fertilizer costs have increased tremendously over the last decades; nitrogen (N) fertilizer prices have doubled in the last two years. Unfortunately, this trend is expected to continue in response to high energy demands and the decreased supply of fossil fuels. The current political instability in the middle-east is directly affecting fuel prices, resulting in even greater increases in fertilizer prices over the last few months.

Bahiagrass has inferior production and nutritive value than other warm-season grasses, such as bermudagrass and stargrass. Research conducted in Wauchula, FL compared the production and nutritive value of ten species and cultivars of warm-season grasses growing in soils with high fertility levels. Bahiagrass was the least productive, but had levels of protein and digestibility that were similar to other species and cultivars when harvested at 6 weeks regrowth interval (Table 1). Despite the inferior production, during the difficult times of high N fertilizer prices, bahiagrass is certainly a good forage species to have. Bahiagrass is more persistent than hybrid bermudagrass, stargrass, and limpograss on extensive production systems with low fertilization levels. The growing points of the bahiagrass tillers are close to the ground, which allows the plant to survive when grazed or harvested at short stubble 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 remaining after grazing or harvest.

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 approximately 12 hours and were removed when the stubble height reached 3 inches. Cows were returned to plots after 2 or 4 weeks 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 limited herbage mass production of all cultivars. Although there was only a slight difference in herbage accumulation among cultivars, grazing frequency significantly affected production. Plots grazed at 4 weeks had 30% greater forage production (Table 2) than those grazed every 2 weeks. Sunlight is the major source of energy for photosynthesis and herbage production. Warm-season grasses reach the optimum production when the leaves are able to intercept approximately 95% of the sunlight. The bahiagrass plots grazed at 4 weeks were able to intercept 91% of the sunlight. Plots grazed at 2 weeks only intercepted 64%. In addition, the plots grazed at 2 weeks had fewer tillers than plots grazed at 4 weeks intervals, which could result in fewer plants per area and an opportunity for weeds. No stand decreases were observed during the first year of the research; however, the decrease in number 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 and intense harvest after a three-year study in Gainesville. Bottom line, bahiagrass production can be improved by allowing longer resting periods. Thus, it is beneficial 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 would increase the average daily gain of the animals; however, it will likely allow increased stocking rates and improve gain per acre.

In general, 1.0 to 1.5 lb of forage (dry matter) per pound of animal liveweight exposed to the pasture provides adequate forage for cow-calf pairs. For example, considering that 1.5 kg DM / kg liveweight is recommended, if the pasture is grazed continuously and 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 and harvested as hay or haylage.

If you have any questions on bahiagrass grazing management, please contact Joe Vendramini, jv@ufl.edu.

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