Comparing ratings of the southern phosphorus indices

D.L. Osmond; M.L. Cabrera; S.E. Feagley; G.E. Hardee; C.C. Mitchell; P.A. Moore; R.S. Mylavarapu; J.L. Oldham; J.C. Stevens; W.O. Thom; F. Walker; H. Zhang

ABSTRACT:

The use of site assessment indices to guide agricultural phosphorus (P) nutrient management has been widely adopted in the United States. This study compares P-index ratings from 12 southern states (Alabama, Arkansas, Florida, Georgia, Kentucky, Louisiana, Mississippi, New Mexico, North Carolina, Oklahoma, South Carolina, Tennessee, and Texas) on fields representing three dominant southern agricultural systems: upland pasture, upland cornfield, and artificially drained field. The structure of each P-index varied enough to produce widely divergent ratings when applied to similar scenarios where individual factors (such as soil test P, poultry broiler litter application rate, or buffer absence or presence) were adjusted across a broad range of P-index input values. Variation in P-index ratings was the unique combination of each state's selected factors, weighting of the factors, and factor combination (added, multiplied, or a mixture of both addition and multiplication). Although the flexibility of and differences among the southern states' P-indices result in dramatically diverse P-index ratings for the same set of conditions, the diversity in P-index construction allows for indices designed to match individual state conditions and concerns. The substantial differences in P-index results identified in this survey highlight the need for close coordination between states in revising P-indices if they are to be applied across state lines.

Footnotes

Deanna L. Osmond is professor of soil science in the Department of Soil Science at North Carolina State University in Raleigh, North Carolina. Miguel L. Cabrera is professor of agronomy in the Department of Crop and Soil Sciences at the University of Georgia in Athens, Georgia. Sam E. Feagley is a professor of soil in the Department of Soil and Crop Science at Texas A&M University in College Station, Texas. Gene E. Hardee is a conservation agronomist in South Carolina's U.S. Department of Agriculture, Natural Resources Conservation Service in Colombia, South Carolina. Charles C. Mitchell is a professor of soil science in the Department of Agronomy and Soils at Auburn University in Auburn, Alabama. Rao S. Mylavarapu is an associate professor of soil and nutrient management in the Soil and Water Science Department at the University of Florida in Gainesville, Florida. Philip A. Moore. Jr. is a soil scientist in the Poultry Production and Product Safety Research Unit with the U.S.Department of Agriculture Agricultural Research Service in Fayetteville, Arkansas. James L. Oldham is an extension professor of soil in the Department of Plant and Soil Sciences, Mississippi State University in Starkville, Mississippi. J. Cheston Steven is an associate extension professor at Louisiana State University in Baton Rouge, Louisiana. William O. Thom is a professor of extension in the Department of Plant and Soil Science at the University of Kentucky in Lexington, Kentucky. Forbes R. Walker is an associate professor of environmental soil in the Department of Biosystems Engineering and Soil Sciences at the University of Tennessee in Knoxville, Tennessee. Hailin Zhang is a professor of nutrient management in the Department of Plant and Soil Sciences at Oklahoma State University in Stillwater, Oklahoma.
Copyright 2006 by the Soil and Water Conservation Society

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