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ARS Home » Midwest Area » Bowling Green, Kentucky » Food Animal Environmental Systems Research » Research » Publications at this Location » Publication #329935
Title: Evaluation of the TBET model for potential improvement of southern P indices

Author
item FORSBERG, ADAM - University Of Georgia
item RADCLIFFE, DAVID - University Of Georgia
item Bolster, Carl
item MITTELSTET, AARON - University Of Nebraska
item STORM, DANIEL - Oklahoma State University
item OSMOND, DEANNA - North Carolina State University

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/3/2017
Publication Date: 3/9/2017
Citation: Forsberg, T.A., Radcliffe, D.E., Bolster, C.H., Mittelstet, A., Storm, D.E., Osmond, D. 2017. Evaluation of the TBET model for potential improvement of southern P indices. Journal of Environmental Quality. doi:10.2134/jeq2016.06.0210.

Interpretive Summary: IA phosphorus index is a commonly used tool for evaluating risk of phosphorus loss from agricultural fields. These tools were designed to require minimal input and expertise to run and thus are much less complicated than traditional models. While commonly used throughout the US, very few of these indices have been tested for accuracy. Because data are limited for evaluating phosphorus indices, many index developers are comparing their index output with more sophisticated models such as the Texas Best Management Evaluation Tool. For this to be a valid method for evaluating a phosphorus index, however, requires that the model being used produces accurate estimates of field-scale phosphorus loss over a wide range of conditions. In this study we compared predictions of field-scale phosphorus loss from TBET with measured phosphorus (P) loss data to determine the accuracy of the model on agricultural fields in the southern US. Overall, the calibrated TBET model seemed to perform better where sediment and particulate P losses were high compared to situations where sediment losses were low and most of the P was lost as dissolved P.

Technical Abstract: Due to a shortage of available phosphorus (P) loss data sets, simulated data from a quantitative P transport model could be used to evaluate a P-index. However, the model would need to accurately predict the P loss data sets that are available. The objective of this study was to compare predictions from the Texas Best Management Evaluation Tool (TBET) against measured P loss data to determine whether the model could be used to improve three P-Indices in the South. Field-scale measured P loss data from study sites in AR, GA, and NC were used to assess the accuracy of TBET for predicting field-scale loss of P. We found that event-based predictions using an uncalibrated model were generally poor. These predictions improved with calibration and TBET predictions of runoff were successful (NSE = 0.3) in two out of three states during calibration and in all three states during validation. However, sediment predictions were imprecise and dissolved P predictions under-estimated losses. Total P predictions using the calibrated model were a matter of getting the right answer for the wrong reasons in AR and GA, over-predicting sediment loss and under-predicting dissolved P loss resulted in reasonably good predictions of total P loss. Overall, the calibrated TBET model seemed to perform better where sediment and particulate P losses were high compared to situations where sediment losses were low and most of the P was lost as dissolved P.