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Title: Regional distribution of soil phosphorus across congregation-grazing zones of forage-based pastures with cow-calf operations in Florida

Author
item Sigua, Gilbert
item MYER, ROBERT - North Florida Research & Education Center
item Coleman, Samuel
item MACKOWIAK, CHERYL - North Florida Research & Education Center
item ADJEI, MARTIN - Range Cattle Research Center
item Chase, Chadwick - Chad
item Albano, Joseph

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/3/2011
Publication Date: 6/29/2011
Citation: Sigua, G.C., Myer, R.O., Coleman, S.W., Mackowiak, C., Adjei, M., Chase, C.C., Albano, J.P. 2011. Regional distribution of soil phosphorus across congregation-grazing zones of forage-based pastures with cow-calf operations in Florida. Journal of Environmental Protection. 2(3):408-417.

Interpretive Summary: Although several studies have documented livestock concentration effects on soil properties under controlled conditions, the effects of animal congregation management that control phosphorus cycling and distribution have not been sufficiently evaluated and reported. Lack of a clear relationship between grazing practices and phosphorus dynamics may be attributed to inherent soil variations, depth of soil sampling, and insufficient evaluation of phosphorus distributions within pasture system. The objectives of this study was to evaluate whether cattle congregation sites such as water troughs and shade areas, typical on most Florida ranches, are more phosphorus-rich and therefore contribute more soluble phosphorus to surface and groundwater supply than in other pasture locations. Soil samples were collected at increasing distance from congregations structures (water troughs and shades) in established (>10 yr), grazed beef cattle pastures located in three Florida regions (north, Marianna; central, Brooksville; and south, Ona). Results from this study suggest that congregation zones in pastures with beef cattle operations are sufficiently not phosphorus-rich to contribute significant phosphorus to surface and groundwater supply under Florida conditions. Average phosphorus in all three-pasture locations did not exceed the crop requirement threshold of 50 mg P kg-1 and the water quality protection threshold of 150 mg P kg-1. Averaged across years, phosphorus concentrations and soil phosphorus saturation of the congregation zones were comparable with soil phosphorus and soil phosphorus saturation in the grazing zones of all the three regions. The degree of soil phosphorus saturation in the pastures were also below the environmental threshold of phosphorus saturation (DPS = 60%), suggesting that phosphorus buildup and/or release is not a predicament anywhere in the pasture, including the congregation zones. These results may have significant implications for the transport of phosphorus to surface waters and our ability to predict and model losses of phosphorus from congregation zone or grazing zone of pastures with cow-calf operations.

Technical Abstract: The arrangement of supplemental feed, water, shelter, and their concurrent interactions with topographic features may influence the distribution of animals and their simultaneous use of pasture’s resources. Grazing can accelerate and alter the timing of nutrient transfers, and could increase the amount of nutrients cycled from soils to plants. The effects of grazing and/or congregation management that control phosphorus cycling and distribution have not been sufficiently evaluated. The objectives of this study were: (a) to determine whether cattle congregation sites typical on most Florida ranches, represented by water troughs and shaded areas, are more phosphorus-rich and may contribute more soluble phosphorus to surface water run-off and groundwater than other pasture locations; and (b) to assess the regional distribution of Mehlich-1 extractable soil phosphorus (MP) across congregation-grazing zones of forage-based pastures with cow-calf operations in Florida. Soil samples were collected at increasing distance from congregations structures (water troughs and shades) in established (>10 yr), grazed beef cattle pastures located in three Florida regions (north, Marianna; central, Brooksville; and south, Ona). Samples were collected in the fall and spring of 2005, 2006, and 2007, respectively; following a radial (every 90 degrees) sampling patterns away from the center of the congregation structures. Mehlich-1 extracted soil phosphorus concentrations were significantly (p=0.001) affected by the interaction of pasture locations and pasture zones. Averaged across years, phosphorus concentrations and soil phosphorus saturation in the congregation zones were comparable (p=0.05) with soil phosphorus values and soil phosphorus saturation in the grazing zones at all three Florida regions. Average MP at all three pasture locations did not exceed the crop requirement threshold of 50 mg P kg-1 and the water quality protection threshold of 150 mg P kg-1. Results of the study suggest that congregation zones in pastures with beef cattle operations in all three regions of Florida are not phosphorus-rich, and therefore may not contribute additional phosphorus to Florida surface and groundwater supplies.