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ARS Home » Midwest Area » Columbia, Missouri » Cropping Systems and Water Quality Research » Research » Publications at this Location » Publication #329877
Title: Calibration of the APEX model to simulate management practice effects on runoff, sediment, and phosphorus loss

Author
item BHANDARI, AMMAR - Kansas State University
item NELSON, NATHAN - Kansas State University
item SWEENEY, DANIEL - Kansas State University
item Baffaut, Claire
item LORY, JOHN - University Of Missouri
item SENAVIRATNE, G.M.M.M. ANOMAA - University Of Missouri
item PIERZYNSKI, GARY - Kansas State University
item JANSSEN, KEITH - Kansas State University
item BARNES, PHILLIP - Kansas State University

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/16/2016
Publication Date: 12/15/2016
Citation: Bhandari, A.B., Nelson, N.O., Sweeney, D.W., Baffaut, C., Lory, J.A., Senaviratne, G., Pierzynski, G.M., Janssen, K.A., Barnes, P.L. 2016. Calibration of the APEX model to simulate management practice effects on runoff, sediment, and phosphorus loss. Journal of Environmental Quality. doi: 10.2134/jeq2016.07.0272.

Interpretive Summary: Computer simulation models are being used to compare the effects of management practices on water quality. For this purpose, they are often calibrated (i.e., input parameters are adjusted so that simulated results match monitoring data) with data specific to a management practice, and then used to test the effect of alternative management systems. However, this use of models has not been fully tested. The objective of this study is to determine if the Agricultural Policy Environmental eXtender (APEX) model, a model that simulates the effects of agricultural management on water quality, can accurately simulate runoff, sediment, total P (TP), and dissolved P (DP) loss from agricultural fields with managements that are different from the calibration data. The APEX model was calibrated with data from eight different managements at two locations (management-specific models). The accuracy of the calibrated models was then tested either with the same management used for calibration or with different managements. Location-specific models were also developed by using data from all the managements together to calibrate APEX. The management-specific models resulted in satisfactory performance when used to simulate runoff, TP and DP on a different watershed with the same management. When applied outside the calibration management, the management-specific models only met the minimum performance criteria in 1/3 of the tests. The location-specific models had better model performance when applied across all managements compared to management-specific models. We recommend that models are only applied within the managements used for calibration and suggest including data from multiple management systems for calibration when using models to assess management effects on P loss. Scientists and water resource managers and planners should be aware of these limitations.

Technical Abstract: Process-based computer models have been proposed as a tool to generate data for phosphorus-index assessment and development. Although models are commonly used to simulate phosphorus (P) loss from agriculture using managements that are different from the calibration data, this use of models has not been fully tested. The objective of this study is to determine if the Agricultural Policy Environmental eXtender (APEX) model can accurately simulate runoff, sediment, total P (TP), and dissolved P (DP) loss from agricultural fields with managements that are different from the calibration data. The APEX model was calibrated with field-scale data from eight different managements at two locations (management-specific models). The calibrated models were then validated either with the same management used for calibration or with different managements. Location-specific models were also developed by calibrating APEX with data from all the managements. The management-specific models resulted in satisfactory performance when used to simulate runoff, TP and DP within their respective systems, with r2 > 0.50, Nash-Sutcliffe efficiency > 0.30, and percent bias within ±35% for runoff and ±70% for TP and DP. When applied outside the calibration management, the management-specific models only met the minimum performance criteria in 1/3 of the tests. The location-specific models had better model performance when applied across all managements compared to management-specific models. We recommend that models are only applied within the managements used for calibration and suggest including data from multiple management systems for calibration when using models to assess management effects on P loss or evaluate P-indices.