The sustainable management of fertilizer and manure P to minimize fres
hwater eutrophication requires identification of soil P levels that ex
ceed crop P requirements and have the potential for P enrichment of ru
noff. Although several states have established such P levels, insuffic
ient data are available to theoretically justify them. Thus, this stud
y investigates the relationship between the concentrations of P in run
off and in soil. Surface samples (0-10 cm) of 10 oklahoma soils were p
acked in 0.15 m(2) boxes, incubated for 7 d with poultry litter (0-20
Mg ha(-1)) to obtain a range in Mehlich-3 P contents (7-360 mg kg(-1))
, and received five 30-min rainfalls applied at 1-d intervals. The con
centration of dissolved, bioavailable, and particulate P in runoff was
related (r(2) > 0.90; P < 0.1) to the Mehlich-3 P content of surface
soil (0-1 cm), with regression slopes ranging from 2.0 to 7.2, increas
ing as soil P sorption maxima increased (r(2) = 0.93). Two soils of 20
0 mg kg(-1) Mehlich-3 P supported a dissolved P concentration in runof
f of 280 mu g L(-1) (San Saba clay; fine, montmorillonitic, thermic Ud
ic Pellustert) and 1360 mu g L(-1) (Stigler silt loam; fine, mixed, th
ermic Aquic Paleudalf). Thus, relationships between runoff and soil P
will have to be soil specific for use in management recommendations. A
single linear relationship described the dependence of dissolved (r(2
) = 0.86) and bioavailable P (r(2) = 0.85) on soil P sorption saturati
on. The added complexity of the P saturation approach may limit its ap
plication; however, the approach integrates the effect of soil type wi
th soil P content to better estimate the potential for P loss in runof
f than soil P alone.