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Journal of Environmental Quality Abstract - Special Section: The Evolving Science Of Phosphorus Site Assessment

Southern Phosphorus Indices, Water Quality Data, and Modeling (APEX, APLE, and TBET) Results: A Comparison


This article in JEQ

  1. unlockOPEN ACCESS
    Received: May 29, 2016
    Accepted: Oct 16, 2016
    Published: July 20, 2017

    * Corresponding author(s): deanna_osmond@ncsu.edu
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  1. Deanna Osmond *a,
  2. Carl Bolsterb,
  3. Andrew Sharpleyc,
  4. Miguel Cabrerad,
  5. Sam Feagleye,
  6. Adam Forsbergd,
  7. Charles Mitchellf,
  8. Rao Mylavarapug,
  9. J. Larry Oldhamh,
  10. David E. Radcliffed,
  11. John J. Ramirez-Avilai,
  12. Dan E. Stormj,
  13. Forbes Walkerk and
  14. Hailin Zhangl
  1. a Crop and Soil Sciences, North Carolina State Univ., Raleigh, NC
    b USDA–ARS, Food Animal Environmental Systems Research Unit, Bowling Green, KY
    c Crop, Soil and Environmental Sciences, Division of Agriculture, Univ. of Arkansas, Fayetteville, AR
    d Crop and Soil Sciences, Univ. of Georgia, Athens, GA
    e Soil and Crop Sciences, Texas A&M Univ., College Station, TX
    f Agronomy and Soils, Auburn Univ., Auburn, AL
    g Soil and Water Science, Univ. of Florida, Gainesville, FL
    h Plant and Soil Sciences, Mississippi State Univ., Starkville, MS
    i Civil and Environmental Engineering, Mississippi State Univ., Starkville, MS
    j Biosystems and Agricultural Engineering, Oklahoma State Univ., Stillwater, OK
    k Biosystems Engineering and Soil Science, Univ. of Tennessee, Knoxville, TN
    l Plant and Soil Sciences, Oklahoma State Univ., Stillwater, OK
Core Ideas:
  • Southern region P Indices estimate P losses as well as water quality models.
  • APLE and TBET P-loss predictions were more similar than were results from APEX.
  • Assigning potential P-loss risk from P Indices to any given water resource is challenging.


Phosphorus (P) Indices in the southern United States frequently produce different recommendations for similar conditions. We compared risk ratings from 12 southern states (Alabama, Arkansas, Florida, Georgia, Kentucky, Louisiana, Mississippi, North Carolina, Oklahoma, South Carolina, Tennessee, and Texas) using data collected from benchmark sites in the South (Arkansas, Georgia, Mississippi, North Carolina, Oklahoma, and Texas). Phosphorus Index ratings were developed using both measured erosion losses from each benchmark site and Revised Universal Soil Loss Equation 2 predictions; mostly, there was no difference in P Index outcome. The derived loss ratings were then compared with measured P loads at the benchmark sites by using equivalent USDA–NRCS P Index ratings and three water quality models (Annual P Loss Estimator [APLE], Agricultural Policy Environmental eXtender [APEX], and Texas Best Management Practice Evaluation Tool [TBET]). Phosphorus indices were finally compared against each other using USDA–NRCS loss ratings model estimate correspondence with USDA–NRCS loss ratings. Correspondence was 61% for APEX, 48% for APLE, and 52% for TBET, with overall P index correspondence at 55%. Additive P Indices (Alabama and Texas) had the lowest USDA–NRCS loss rating correspondence (31%), while the multiplicative (Arkansas, Florida, Louisiana, Mississippi, South Carolina, and Tennessee) and component (Georgia, Kentucky, and North Carolina) indices had similar USDA–NRCS loss rating correspondence—60 and 64%, respectively. Analysis using Kendall’s modified Tau suggested that correlations between measured and calculated P-loss ratings were similar or better for most P Indices than the models.

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