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The six soil-supplied nutrients required by plants in the largest quantities are nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sulfur (S). Micronutrents (iron, copper, zinc, manganese, boron, molybdenum, and chlorine) are also essential but are used by the plant in very small amounts. The soil can supply the plant with most, if not all, of these nutrients, but often the supply of one or more of the nutrients is insufficient for optimum growth.
Nitrogen is the most important fertilizer nutrient used on grass pastures. It is the nutrient that is most likely to be deficient and therefore the one that most often results in increased forage production. Phosphorus may be deficient in some areas, but some Florida soils are high in native P. Also, some grasses may extract sufficient P from the subsoil, even when the P level in the surface soil is low. Potassium may need to be added to some pastures. The other nutrients are seldom a problem in pastures where considerable recycling of these nutrients occur. Under intensive hay or silage production, where nutrients are removed from the land, annual applications of P and K are needed. Potassium can very quickly become deficient. Calcium, magnesium, sulfur, and some micronutrients may also become deficient.
Fertilizer should usually be applied at the beginning of the growing season for the particular forage in question. Warm-season perennial grasses should be fertilized in the early spring (February to March)--this stimulates needed production at a critical time. Some pasture grasses may be given an additional application of nitrogen in June if extra forage is needed, but this is usually not the case for a beef cow/calf operation. Although bahiagrass gives little, if any, response to a late-summer/fall application, limpograss, rhodesgrass, and stargrass do. These grasses can be fertilized in the late summer or early fall to extend the grazing season or, in the case of limpograss, for stockpiling. Timely application of fertilizer can be used to increase forage yield and quality, improve stand persistence, and provide for better distribution of forage across the growing season. The producer should consider that the response obtained from an application of fertilizer is influenced by many other factors such as solar radiation, temperature, soil moisture, and grazing management. Overgrazing (excessive defoliation) limits the plants' ability to respond to the added nutrients and thereby reduces potential yield.
Some grasses, such as the stargrasses and some of the improved hybrid bermudagrasses, need to be fertilized annually or maintained in a high-fertility environment in order to maintain a good stand. On the other hand, some ranch managers with large, extensive operations may only fertilize their bahiagrass or limpograss once every three years. These grasses can persist under minimum fertility if they are not overgrazed.
Source: Chambliss, C.G., and G. Kidder. 2003. Fertilizing and Liming Forage Crops. SS-AGR-176. University of Florida Extension Service. Gainesville, FL. Available at http://edis.ifas.ufl.edu/AG179 (verified 19 August 2004).