Dh. Pote et al., RELATING EXTRACTABLE SOIL-PHOSPHORUS TO PHOSPHORUS LOSSES IN RUNOFF, Soil Science Society of America journal, 60(3), 1996, pp. 855-859
Phosphorus in agricultural runoff can cause accelerated lake and strea
m eutrophication. Where producers have applied P at rates exceeding cr
op uptake, soil P has sometimes become the main source of P in runoff.
We hypothesized that soil test P (STP) correlation to dissolved react
ive P (DRP) and bioavailable P (BAP) in runoff varies, depending on th
e extraction method. To investigate which STP extraction method would
be best for predicting DRP and BAP concentration and load in runoff, s
oil samples were taken from the 0- to 2-cm depth of 54 grass plots (5%
slopes) on Captina silt loam (fine-silty, siliceous, mesic Typic Frag
iudult). The STP was extracted by six methods and the ranges of result
s (mg kg(-1)) were: 54-490 (Mehlich III), 27-592 (Bray-Kurtz P1), 25-1
69 (Olsen), 14-110 (distilled water), 23-170 (Fe oxide paper), and 105
-1131 (acidified ammonium oxalate). The soil P saturation ranged from
16 to 80%. Simulated rain was applied at 100 mm h(-1) and runoff was c
ollected for 30 min. The concentration of DRP in total runoff ranged f
rom 0.31 to 1.81 mg L(-1), and BAP from 0.37 to 2.18 mg L(-1). The r(2
) values for STP by each extraction method correlated with runoff DRP
and BAP, respectively, were: 0.72 and 0.72 (Mehlich III), 0.75 and 0.7
3 (Bray-Kurtz P1), 0.72 and 0.72 (Olsen), 0.82 and 0.82 (distilled wat
er), 0.82 and 0.82 (iron oxide paper), 0.85 and 0.82 (acidified ammoni
um oxalate), and 0.77 and 0.76 (P-saturation). All correlations were s
ignificant (P < 0.001), but the high r(2) values of those obtained fro
m distilled water, iron oxide paper, and acidified ammonium oxalate ex
tractants indicate better precision for predicting DRP and BAP concent
rations in runoff. Correlations of STP with DRP load (range: 43.4 to 4
72.8 g ha(-1)) and BAP load (54.2 to 542.0 g ha(-1)) were not useful (
r(2) < 0.18), possibly because runoff volumes were highly variable.