Vd. Nair et al., FORMS OF PHOSPHORUS IN SOIL PROFILES FROM DAIRIES OF SOUTH FLORIDA, Soil Science Society of America journal, 59(5), 1995, pp. 1244-1249
Soil P fractions of current and abandoned dairy systems in South Flori
da's Lake Okeechobee watershed were evaluated to develop an understand
ing of the stability of P in this basin. Land use within the dairies,v
as classified as intensive (high cattle impacted) and pasture, forage,
or native (low cattle impacted) areas. All soils (Spodosols) were cha
racterized for labile P (1 M NE(4)Cl), Fe-Al-associated P (0.1 MNaOH),
Ca-Mg-associated P (0.5 M HCl), residual P, and organic P in the NaOH
fraction. The A horizons of the intensive areas had approximate to 9%
of total P as labile P, though most of the Ca-Mg-associated P (approx
imate to 7% of total P) in these particular systems could also be remo
ved by sequential NH4Cl extractions. Therefore, almost 80% of the P in
the surface horizons of the high cattle impacted areas had the potent
ial to move eventually with drainage water into the lake. The P in the
E horizons of the intensive areas consisted primarily of labile P and
Ca-Mg-associated P forms as well, though the total P in these horizon
s was <5% of that for the A horizons. About 80% of the total P in the
spodic (Bh) horizons was extractable by NaOH, of which only 4 to 18% w
as associated with organic matter, The total P contents for all horizo
ns of the soil profiles from the low cattle impacted areas were consid
erably less than those from the high cattle impacted areas. There were
apparently no major shifts of P to more stable P forms, with time, fo
r soils of high cattle impacted areas. Therefore, the possibility of P
release from high cattle impacted soils, even after dairies were aban
doned for more than 12 yr, cannot be ruled out.