Submitted to: Journal of Soils and Sediments
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/5/2003
Publication Date: 12/15/2003
Citation: Sigua, G.C. 2003. Soils and environment of grazed pasture ecosystems in subtropical United States: Trends and research results. Journal of Soils and Sediments. 3(4):258-260.
Interpretive Summary: Throughout the southeastern United States, grazinglands have considerable variability in soils, climate, and growing season, which not only affect the types of forage that can be grown, but also the overall biodiversity, management, and temporal/spatial nutrient dynamics. In the southeastern United States, particularly, Florida, most of the grazing areas are located on coastal plain (flatwood) soils. Flatwood soils comprise about 51% of Florida soils and are dominated by forestry, beef cattle, citrus, vegetable, and dairy operations. The dominant soils are aquouds, aquents, and aquepts. Because the land is flat and poorly drained, most of the runoff occurs when the water table is close to the surface during the rainy season, June to October. During that time, runoff can be high in the area because the soils are sandy spodosols, which have low nutrient retention capacity, especially phosphorus (P), causing high P losses to occur. Beef cattle operations have been suggested as one of the major sources of non-point source P pollution that is contributing to the degradation of water quality in lakes, reservoirs, rivers, and ground-water aquifers. Our long-term monitoring could provide answers about the nutrient cycling and turnover in systems involving legumes-grass mixtures and the efficiency of fertilizer use. Knowledge of the relationship of temporal and spatial changes in soil nutrient levels may provide insights for improved grazing management, which could be both economically and environmentally prudent. For this reason, soil fertility levels over a 15-year period (1988-2002) were compared to evaluate the long-term effects of differing fertility (P or no P) and management treatments (grazed only or grazed and hayed) on soil P and other crop nutrients in subtropical pastures planted with bahiagrass or rhizoma peanut-mixed grass association. During the past 15 years, average soil test values for P, K, Ca and Mg have declined by about 32%, 51%, 61% and 58%, respectively, but this decline varied with pasture management.
Technical Abstract: Beef cattle producers throughout the United States need better forage management systems to reduce input costs and protect environmental quality. This is particularly true in the 11 million hectares classified as grazingland in the subtropical (23.5 - 30oN Lat) United States due to climatically mediated dependence on tropical forages. Throughout the southeastern United States, grazinglands have considerable variability in soils, climate, and growing season, which not only affect the types of forage that can be grown, but also the overall biodiversity, management, and temporal/spatial nutrient dynamics. In the southeastern United States, particularly, Florida (FL), most of the grazing areas are located on coastal plain (flatwood) soils. The average soil test values for P, K, Ca and Mg of subtropical beef cattle pastures in south central FL have declined by about 12%, 37%, 50% and 30%, respectively, during the past 15 years. Phosphorous levels in the grazed only bahiagrass pastures were essentially unchanged after 15 years without P fertilization. Potassium levels have also remained unchanged indicating that K fertilization rates have been adequate to maintain the levels present in 1988. This occurs because grazing, for most part, recycles most the nutrient back into the forage system. The combination of grazing in spring and haying in early fall can be considered a good pasture management (i.e., BMP) in maintaining nutrient balance in the pasture fields, thereby avoiding a potential negative impact on the environment. Over the next decade, forage-based livestock systems still will be implicated as major contributors to deteriorating water quality, particularly for phosphorous in fertilizers and manures impacting surface and ground water quality. The traditional importance of pure economic considerations in decision making now must be balanced with societal concerns as to how livestock production will impact environmental quality. Forage-beef cattle research programs must adopt an integrated approach that will lead to the development of appropriate sustainable pasture management technologies. The scope of this problem will necessitate strong collaborative work across numerous disciplines and locations.