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This article in JEQ

  1. Vol. 41 No. 6, p. 1741-1749
    Received: Jan 6, 2012
    Published: October 16, 2012

    * Corresponding author(s): deanna_osmond@ncsu.edu
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Comparing Phosphorus Indices from Twelve Southern U.S. States against Monitored Phosphorus Loads from Six Prior Southern Studies

  1. D. Osmond *a,
  2. A. Sharpleyb,
  3. C. Bolsterc,
  4. M. Cabrerad,
  5. S. Feagleye,
  6. B. Leef,
  7. C. Mitchellg,
  8. R. Mylavarapuh,
  9. L. Oldhami,
  10. F. Walkerj and
  11. H. Zhangk
  1. a Soil Science Dep., North Carolina State Univ., Raleigh, NC
    b Dep. of Crop, Soil and Environmental Sciences, Division of Agriculture, Univ. of Arkansas, Fayetteville, AR
    c USDA–ARS, Animal Waste Management Research Unit, Bowling Green, KY
    d Dep. of Crop and Soil Sciences, Univ. of Georgia, Athens, GA
    e Dep. of Soil and Crop Sciences, Texas A&M Univ., College Station, TX
    f Plant and Soil Science, Univ. of Kentucky, Lexington, KY
    g Dep. of Agronomy and Soils, Auburn Univ., Auburn, AL
    h Soil and Water Science Dep., Univ. of Florida, Gainesville, FL
    i Dep. of Crop and Soil Science, Mississippi State Univ., Starkville, MS
    j Dep. of Biosystems Engineering and Soil Science, Univ. of Tennessee, Knoxville, TN
    k Dep. of Plant and Soil Sciences, Oklahoma State Univ., Stillwater, OK. Assigned to Associate Editor Peter Vadas


Forty-eight states in the United States use phosphorus (P) indices to meet the requirements of their Natural Resources Conservation Service (NRCS) Code 590 Standard, which provides national guidance for nutrient management of agricultural lands. The majority of states developed these indices without consultation or coordination with neighboring states to meet specific local conditions and policy needs. Using water quality and land treatment data from six previously published articles, we compared P loads with P-Index values and ratings using the 12 southern P indices. When total measured P loads were regressed with P-Index rating values, moderate to very strong relationships (0.50 to 0.97) existed for five indices (Arkansas, Florida, Georgia, North Carolina, and South Carolina) and all but one index was directionally correct. Regressions with dissolved P were also moderate to very strong (r2 of 0.55 to 0.95) for the same five state P indices (Arkansas, Florida, Georgia, North Carolina, and South Carolina); directionality of the Alabama Index was negative. When total measured P loads were transformed to current NRCS 590 Standard ratings (Low [<2.2 kg P ha−1], Moderate, [2.2–5.5 kg P ha−1], and High [>5.5 kg P ha−1]) and these ratings were then compared to the southern-Index ratings, many of the P indices correctly identified Low losses (77%), but most did not correctly identify Moderate or High loss situations (14 and 31%, respectively). This study demonstrates that while many of the P indices were directionally correct relative to the measured water quality data, there is a large variability among southern P indices that may result in different P management strategies being employed under similar conditions.

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Copyright © 2012. Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.