FORMS OF PHOSPHORUS IN SOIL PROFILES FROM DAIRIES OF SOUTH FLORIDA

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.