Phosphorus accumulation in manure-impacted Spodosols of Florida

Abstract

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. Land areas of both active and abandoned dairies were sampled based on estimated cattle density. High cattle-density areas of both the active and abandoned dairies, i.e., the intensive and holding areas, had mean total phosphorus (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 cattle pastures and the forage areas (low cattle density areas) had a mean TP concentration of 114 mg kg −1. Concentrations of TP in the E, Bh, and Bw soil horizons were also greater in the high cattle density areas than in the low cattle density areas or in the native areas. Water-soluble P concentrations (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-soluble P concentrations in the surface horizons of the high cattle density areas averaged 3.4% of TP which suggests that a substantial amount of P could be transported either vertically or laterally with subsurface drainage. Double acid-extractable P (DAP) concentrations, which could be used as an indicator of potentially leachable P, were considerably higher than WSP concentrations and averaged (over 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 relationship 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 forms 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 density areas confirm the downward transport of P in these manure-laden Spodosols.