Submitted to: Journal of Soil and Water Conservation Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 9, 2004
Publication Date: January 20, 2005
Citation: Harmel, R.D., Torbert III, H.A., Delaune, P.B., Haggard, B.E., Haney, R.L. 2005. Field evaluation of three phosphorus indices on new application sites in Texas. Journal of Soil and Water Conservation Society. 60(1):29-42. Interpretive Summary: With the expansion of the poultry industry and increased litter application to agricultural lands, management tools are needed to limit negative environmental impacts associated with excessive nutrients such as phosphorus (P) and nitrogen (N) in water. The focus of this study is the evaluation of three variations of one such tool, the Phosphorus Index or the P Index, which was developed to determine areas susceptible to excessive phosphorus loss. To accomplish this goal, we determined P Index values using the Texas, Arkansas, and Iowa methods for four pasture and six cropland fields and compared to them to measured phosphorus losses before and after poultry litter application. In the fallow year, the P Indices did not accurately represent P loss; however, when litter application began and soil P levels increased, the performance of all three P Indices improved. The P Index methods did perform relatively well in ranking the fields based on P losses. In words, fields that had high P index values tended to have relatively high P losses. Results indicated that the three P Indices accomplished their purpose of estimating the relative susceptibility of fields to excessive P loss.
Technical Abstract: The phosphorus (P) Index was developed to address nonpoint source P losses from agricultural fields. The ability of three P Indices (Arkansas, Iowa, and Texas) to estimate P loss potential was evaluated over three years on ten new litter application sites in the Texas Blackland Prairie. Water quality monitoring on pasture and cultivated watersheds was initiated in 2000 prior to poultry litter application and continued after litter was applied in 2001 and 2002. In the fallow year, the P Indices did not accurately represent P loss; however, when litter application began and soil P levels increased, the performance of all three P Indices improved. Even though considerable variability existed, P Index values were correlated to P loss. Phosphorus Index values also correlated well with both average and maximum annual dissolved P concentrations in runoff. Results indicated that the three P Indices accomplished their specified purpose of estimating the relative susceptibility of fields to excessive P loss.