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United States Department of Agriculture

Agricultural Research Service

Title: Relating Extractable Soil Phosphorus to Phosphorus Losses in Runoff

Authors
item Pote, D. - UNIV OF ARKANSAS
item Daniel, T. - UNIV OF ARKANSAS
item Sharpley, Andrew
item MOORE, PHILIP
item Edwards, D. - UNIV OF ARKANSAS
item Nichols, D. - UNIV OF ARKANSAS

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 10, 1996
Publication Date: N/A

Interpretive Summary: Phosphorus runoff from agricultural fields can cause eutrophication in lakes and rivers. Where crop and livestock producers have applied P for decades at rates exceeding crop uptake, soil P has sometimes become the main source of P in runoff. We hypothesized that soil test P (STP) correlation to dissolved reactive P (DRP) and bioavailable P (BAP) in runoff varies, depending on the extraction method. In a field study at Fayetteville, Arkansas to investigate which STP extraction method would be most useful for predicting DRP and BAP concentration and load in runoff, soil samples were taken from the 0-2 cm depth of 54 grass plots (5% slopes) on Captina silt loam. Simulated rainfall was applied at 100 mm h-1 and runoff was collected for 30 min from each plot. The concentration of DRP in total runoff ranged from 0.31 to 1.81 mg L-1, and BAP from 0.37 to 2.18 mg L-1. The r2 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 0.73 (Bray-Kurtz P1), 0.72 and 0.72 (Olsen), 0.82 and 0.82 (distilled water), 0.82 and 0.82 (iron oxide paper), 0.85 and 0.82 (acidified ammonium oxalate), and 0.77 and 0.76 (P-saturation).

Technical Abstract: Phosphorus (P) in agricultural runoff can cause accelerated eutrophication. Where livestock producers have applied P for decades at rates exceeding crop uptake, soil P has sometimes become the main source of P in runoff. We hypothesized that soil test P (STP) correlation to dissolved reactive P (DRP) and bioavailable P (BAP) in runoff varies, depending on the extraction method. In a field study at Fayetteville, Arkansas to investigate which STP extraction method would be most useful for predicting DRP and BAP concentration and load in runoff, soil samples were taken from the 0-2 cm depth of 54 grass plots (5% slopes) on Captina silt loam (fine-silty, siliceous, mesic Typic Fragiudult). The STP was extracted by six methods and the ranges of results (mg kg-1) were: 54-490 (Mehlich III), 27-592 (Bray-Kurtz P1), 25-169 (Olsen), 14-110 (distilled water), 23-170 (iron oxide paper), and 105-1131 (acidified ammonium oxalate). The P saturation of the soil ranged from 16 to 80%. Simulated rainfall was applied at 100 mm h-1 and runoff was collected for 30 min from each plot. The concentration of DRP in total runoff ranged from 0.31 to 1.81 mg L-1, and BAP from 0.37 to 2.18 mg L-1. The r2 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 0.73 (Bray-Kurtz P1), 0.72 and 0.72 (Olsen), 0.82 and 0.82 (distilled water), 0.82 and 0.82 (iron oxide paper), 0.85 and 0.82 (acidified ammonium oxalate), and 0.77 and 0.76 (P-saturation). All of these correlations were significant (p<0.001), but the high r2 values of those obtained from distilled water, iron oxide paper, and acidified ammonium oxalate extractants indicate better precision for predicting DRP and BAP concentrations in runoff.

Last Modified: 8/19/2014
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