Bermudagrass is a deeprooted, warmseason perennial grass grown throughout the South for pasture and hay. Bermudagrass is adapted to a wide variety of soils and climatic conditions and is more tolerant of frequent or intense grazing than bunchgrasses. Well-fertilized bermudagrass can provide more grazing than most other warmseason grasses. However, bermudagrass is not as productive or persistent under low fertility as other grasses.
Fertilizer is the second most important factor (behind rainfall and/or irrigation) that limits forage production of bermudagrass. Nitrogen is the nutrient that limits forage production the most. In the real world it is difficult for us to separate out rainfall and fertility.
Haying is a process that "mines" the soil. For each 1,000 pound round bale that leaves a field it takes with it about 20 lb. of nitrogen, 3 lb. of actual phosphorus, and 20 lb. of potash. Other nutrients, such as sulfur, calcium, magnesium, and micronutrients, are also removed. In many cases the soil may supply most of these nutrients, except for nitrogen, for many years. The only way to avoid nutrient deficiencies is to soil test and fertilize accordingly.
If the bermudagrass is grazed, a portion of the fertilizer nutrients are recycled as urine and manure. However, the efficiency of this recycling depends on weather and grazing management. Hot, windy days increase the amount of nitrogen that is lost back to the atmosphere. Grazing animals also tend to loaf in certain areas, such as shade, watering, and feeding areas, which concentrates the nutrients on smaller areas in the pasture. The efficiency of nutrient recycling can be improved with good grazing management. This will gradually reduce the fertilizer inputs needed, but the likelihood of maintaining production without any fertilizer is very small.
Three valuable things generally occur as the nitrogen rate increases:
- yields increase,
- crude protein of the forage increases,
- efficiency of rainfall in producing forage improves.
In addition, the increased vigor of the bermudagrass sod reduces weed competition and soil erosion.
Nitrogen is the nutrient that is utilized most efficiently by bermudagrass. Nitrogen should be applied based on a realistic yield goal. Research has shown that for each additional pound of actual nitrogen applied bermudagrass yields will increase by about 25 lb. in Oklahoma and 30 lb. in Texas. The higher value for Texas is due to the longer growing season and is an average of several locations scattered throughout the state.
Nitrogen is subject to leaching, and efficiency can be improved by splitting the applications throughout the growing season. Continued use of nitrogen will decrease the soil pH over time, and lime will be needed.
Phosphorus does not move much in the soil relative to the other nutrients and can be applied as a single application. Phosphorus can be applied in the fall if the bermudagrass is overseeded with ryegrass, small grains or legumes. Soil test recommendations should be specific to these overseeded crops because they have a higher requirement for phosphorus than the bermudagrass.
Potash is somewhat subject to leaching but not as much as nitrogen. For this reason, potash can either be applied as a single application early in the growing season or split into several applications to improve the efficiency of the fertilizer. Low soil levels of potash can lead to reduced yields, poor stands and winterkill.
When it comes to applying fertilizer materials other than nitrogen, any rule-of-thumb is poor when compared to a soil test for nutrients. Without a soil test, you may be under-fertilizing and not producing the optimum amount of forage, or over-fertilizing and spending money that could best be spent elsewhere.