ARS | Publication request: Do Plot Studies Generate “Directionally” Correct Assessments of Field Level Phosphorus Losses?

Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 4, 2010
Publication Date: September 1, 2010
Repository URL: http://hdl.handle.net/10113/46001
Citation: Smith, D.R., Pappas, E.A. 2010. Do Plot Studies Generate “Directionally” Correct Assessments of Field Level Phosphorus Losses? Journal of Soil and Water Conservation. 65(5):289-297.

Interpretive Summary: There has been a tremendous amount of research in recent years to determine how management at the field level will impact water quality. The vast majority of this research has been conducted at the plot (i.e. approximately 20 sq ft) scale. We conducted this research to determine if plot scale research could be used to determine differences in phosphorus transport from fields that were managed differently. Soluble phosphorus and total phosphorus losses were generally “directionally” correct, meaning that plots that had greater phosphorus losses were located in the fields with greater phosphorus losses. The impact of this research is that it appears to validate the use of plot scale data to evaluate how management practices affect phosphorus transport at the field scale.

Technical Abstract: The National P Research Project (NPRP) coordinated a tremendous amount of research at the plot scale to assess the influence of nutrient management on P transport at the fields scale. The objectives of this research were to determine of plot scale rainfall simulations could be used to assess P transport from fields that were managed differently. Plots were constructed within the management zone, but adjacent to monitored fields. Phosphorus transport at the field scale from throughout the growing season were compared to confidence limits established by the rainfall simulations, and a secondary analysis compared values from individual storms to the rainfall simulations. Soluble P (SP) and total P (TP) loads were generally directionally correct, but the values obtained from plots were not necessarily similar to those observed at the field scale. Precipitation normalized loads for SP and TP were the most similar metric when comparing values from the plot to the field scale (i.e. more field scale values fell within the 95% confidence limits set by the plot data than the other metrics). Using cumulative field scale data from each year or the mean values from storms by year did not appear to change the results of this study. This study would appear to confirm that the management decisions based on the NPRP are most likely to be sound, and will probably lead to improved quality of runoff water from fields. Precipitation normalized loads appears to be a metric that may provide additional insight into P transport at various scales.