Sustainable management of nutrients in forage-based pasture soils: effect of animal congregation sites.

Authors: Sigua, Gilbert; Coleman, Samuel

Submitted to: Journal of Soils and Sediments
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/29/2007
Publication Date: 2/6/2007
Citation: Sigua, G.C., Coleman, S.W. 2007. Sustainable management of nutrients in forage-based pasture soils: effect of animal congregation sites. Journal of Soils and Sediments.6(4):249-253.

Interpretive Summary: Grazing animals affect the movement and utilization of nutrients through the soil and plant system, and thus affect the fertility of pasture soils. Grazing can accelerate and alter the timing of nutrient transfers, and increase the amount of nutrients cycled from plant to soil. Grazing duration, position of shade, and water resources for grazing cattle can influence the spatial distribution of soil biochemical properties including soil organic carbon , total extractable inorganic nitrogen (TIN) , and total extractable phosphorus (TP). Baseline soil samples around and beneath three congregation sites in established (>10 yr) pastures grazed by beef cattle at the United States Department of Agriculture, Agricultural Research Service (ARS), Subtropical Agricultural Research Station, Brooksville, FL, were collected in 2003, 2004, and 2005. Our reason for conducting this study was to determine whether cattle congregation sites typical on most Florida ranches, such as mineral feeders, water troughs, and shade areas are more nutrient-rich with potential to contribute more nutrients to surface and groundwater supply than in other pasture locations. The levels of soil TIN and TP were affected by the interaction of congregation sites and distance away from the center of the sites. Mineral feeders had the highest concentration of TP followed by shades and water troughs. However, the level of TP around the water troughs does not appear to change significantly with distance, averaging about 13-18 mg/kg. The levels of TIN decreased linearly with distance away from the mineral feeders from the center of the shades. Early results of the study suggest cattle congregation sites in beef cattle operations in Florida are not as nutrient-rich as anticipated, therefore are not likely major contributors of nutrients to surface and groundwater supply. Further research is continuing, including sampling at cattle congregation sites at other locations in north and south Florida.

Technical Abstract: Grazing can accelerate and alter the timing of nutrient transfers, and increase the amount of nutrients cycled from plant to soil. Grazing duration, position of shade, and water resources for grazing cattle can influence the spatial distribution of soil biochemical properties including soil organic carbon, total inorganic nitrogen (TIN), and phosphorus (TP). Our reason for conducting this study was to test whether cattle congregation sites typical on most Florida ranches, such as mineral feeders, water troughs, and shade areas are more nutrient-rich and may contribute more nutrients to surface and groundwater supply than in other pasture locations. The levels of soil TIN and TP were significantly (p less than 0.001) affected by the interaction of congregation sites and distance away from the center of the sites. Mineral feeders had the highest concentration of TP followed by shades and water troughs. The concentrations of soil TP decreased almost linearly with distance away from the center of the mineral feeders (-5.24x + 55.10; R2 = 0.92; p less than 0.001) and the shades (-6.25x + 57.21; R2 = 0.85; p less than 0.001). However, the level of TP around the water troughs (-0.25x + 16.91; R2 = 0.09) does not appear to change significantly with distance, averaging to about 13 -18 mg/kg. The levels of TIN decreased linearly with distance from the mineral feeders and from the center of the shades. A linear model can describe the relationship between TIN and distance away from the center of shades: -11.3x + 78.2; R2 = 0.95; p less than 0.001. The shaded sites (34.2 mg/kg) had either higher levels than the mineral feeders (7.2 mg/kg) or water troughs (10.1 mg/kg) sites. The higher soil TP near and around the mineral feeders can be probably attributed to the presence of phosphorus in the supplemental feeds. Higher TIN content at the shade sites are more likely due to increased defecation and urination of animals and lack of vegetation immediately adjacent to shades. The lack or total absence of vegetation within and/or near the shades had no uptake mechanism for removal of inorganic nitrogen, unlike the heavy demand for inorganic nitrogen by bahiagrass in other areas of the pasture. An accumulation of TIN immediately adjacent to shades could lead to a potential point source that would be susceptible to leaching or gaseous losses to the environment.