Phosphorus accumulation in manure-impacted Spodosols of Florida

Accumulation of phosphorus (P) in soils receiving long-term application of manure has been linked with degradation of water quality in nearby streams and lakes. The objective of this research was to determine the amounts and depth distribution of phosphorus (P) in Florida Spodosols used for dairies and beef ranches, and to relate them to various soil chemical parameters. L and areas of both active and abandoned dairies were sampled based on estima ted cattle density. High cattle-density areas of both the active and abando ned dairies, i.e., the intensive and holding areas, had mean total phosphor us (TP) concentrations in the surface horizon (A) of 2500 mg kg(-1) and 750 mg kg(-1), respectively compared to 30 mg kg(-1) in the native area, i,e., an area largely unimpacted by animals and humans. The dairy and beef cattl e pastures and the forage areas (low cattle density areas) had a mean TP co ncentration of 114 mg kg(-1). Concentrations of TP in the E, Bh, and Bw soi l horizons were also greater in the high cattle density areas than in the l ow cattle density areas or in the native areas. Water-soluble P concentrati ons (WSP) were higher in all soil horizons of the high cattle density areas compared to the low cattle density areas and the native areas. Water-solub le P concentrations in the surface horizons of the high cattle density area s averaged 3.4% of TP which suggests that a substantial amount of P could b e transported either vertically or laterally with subsurface drainage. Doub le acid-extractable P (DAP) concentrations, which could be used as an indic ator of potentially leachable P, were considerably higher than WSP concentr ations and averaged lover all land-uses) 42, 44, 57 and 31% of TP for the A , E, Bh, and Bw horizons, respectively. The association of WSP, DAP, and TP with the soil chemical parameters measured in this study showed a varied r elationship with double acid-extractable Ca and Mg and oxalate-extractable Fe and Al. Overall, these results show the accumulation of large amounts of P in high cattle density areas. Significant amounts of this P were in form s that are potentially leachable, i,e., WSP and DAP. Higher concentrations of all P forms in the subsurface horizons (E, Bh, Bw) of high cattle densit y areas confirm the downward transport of P in these manure-laden Spodosols . (C) 1999 Elsevier Science B.V. All rights reserved.