Phosphorus loading from dairies and beef ranches in the Lake Okeechobe
e watershed and the subsequent movement of the P into the drainage wat
ers is a major factor influencing the eutrophication of Lake Okeechobe
e. The soils of this area are mainly Spodosols with the watertable lyi
ng between surface and spodic horizons for extended periods each year.
In this study, the quantity of total P (TP) within the soil profile (
A, E, Ph and Bw horizons) of dairies and beef ranches in the Lake Okee
chobee basin was determined to evaluate the magnitude of P loading in
these soils. The effect of cattle density was evident in TP concentrat
ions throughout the soil profile. In the A horizon, mean TP concentrat
ions were 1680, 165, and 34 kg P ha-l for high, low, and nonimpacted a
reas, respectively. The same trend, although at lower concentrations,
was evident in the E, Bh, and Bw horizons. The quantity of P considere
d to be potentially mobile under leaching conditions (water-soluble P,
Mehlich I extractable or NH4Cl extractable), also followed similar tr
ends as the TP concentrations. Based on chemical fractionation data, n
early 80% of TP in the A horizon of the highly impacted soils may be c
onsidered leachable. We calculated that about 4000 kg P ha(-1) would b
e available for leaching in the soil profile of the high intensity are
as immediately adjacent to the dairy barns. This ''labile P'' appears
to be solubilized slowly over a long period of time (likely several ye
ars). There seems to be no natural mechanism whereby the P is stabiliz
ed through the formation of minerals, and even if such processes do ta
ke place, a vast amount of P still remains in a form in which it is re
adily transported along with the drainage water. The A and E horizons
had poor P retention capacities while the retention capacity of the Bh
horizon varied with the soil type, Myakka greater than or equal to Im
mokalee > Pomello. Due to the low P-retention capacity in the upper ho
rizons of these soils, there is potential for significant subsurface l
ateral P transport.