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A critical evaluation of the Kentucky phosphorus index

Bolster, Carl H.
Transactions of the Kentucky Academy of Science. 2011 v.72 no.1 pp. 46
Natural Resources Conservation Service, agricultural management models, agricultural soils, fertilizer rates, losses from soil, nonpoint source pollution, nutrient management, phosphorus, phosphorus fertilizers, risk, soil erosion, waterways, Kentucky
The U.S. Department of Agriculture's Natural Resource Conservation Service (USDA-NRCS) is currently revising its 590 Nutrient Management Conservation Standard. As part of this revision, USDA-NRCS is considering requiring states to test the accuracy of their phosphorus (P) indices using either measured P loss data or simulated P loss data generated from process-based models. The objective of this study was to critically evaluate the KY P index by comparing index output with simulated P loss data obtained from a validated P loss model. Furthermore, the general formulation of the index was evaluated against current research on the processes controlling P transport in the environment. Results suggested that in some areas the index does a good job in assigning P loss risk; however, this analysis also showed some important deficiencies in the index, primarily the neglect of important factors known to affect P loss (e.g., soil erosion and P application rates) and how the different factors in the index are weighted. To reduce the amount of P that is exported from agricultural fields to waterways within Kentucky, resources should be devoted to revising the KY P index to address these limitations as well as developing long-term monitoring sites where the P index and more process-based models can be evaluated against measured P loss data.