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ARS Home » Midwest Area » Columbia, Missouri » Cropping Systems and Water Quality Research » Research » Publications at this Location » Publication #312741
Title: Multi-site evaluation of APEX for crop and grazing land in the Heartland region of the US

Author
item Baffaut, Claire
item NELSON, NATHAN - Kansas State University
item SENAVIRATNE, ANOMAA - University Of Missouri
item BANDHARI, AMMAR - Kansas State University
item VAN LIEW, MIKE - University Of Nebraska
item UDAWATTA, RANJITH - University Of Missouri
item LORY, JOHN - University Of Missouri

Submitted to: Annual International SWAT Conference
Publication Type: Proceedings
Publication Acceptance Date: 12/5/2014
Publication Date: 12/18/2014
Citation: Baffaut, C., Nelson, N., Senaviratne, A., Bandhari, A., Van Liew, M., Udawatta, R., Lory, J. 2014. Multi-site evaluation of APEX for crop and grazing land in the Heartland region of the US. Annual International SWAT Conference. P. 73.

Interpretive Summary: The Agricultural and Policy Environmental Extender (APEX) is capable of estimating edge-of-field water, nutrient, and sediment transport and is used to assess the environmental impacts of agricultural management practices. The program requires hundreds of input parameters that describe the field and control how processes are simulated. Current parameterization practice is to adjust some of these parameters based on the comparison of simulated flow and water quality with measured data, which requires resources and data that are not always available. The objective of this study was to compare annual simulated flow, sediment and phosphorus transport under two parameterization strategies: a best professional judgment (BPJ) parameterization based on readily available data and a fully calibrated parameterization based on site specific soil, weather, event flow and water quality data. The analysis was conducted using data from 19 sites at four different locations representing conditions ranging from well to poorly drained soils and agricultural systems covering row crop under different tillage systems and grazing systems. Although the BPJ model performance for flow was acceptable, calibration using site specific data improved it. Acceptable simulation of sediment and total phosphorus transport was obtained only after full calibration at each site. Given the unacceptable performance of the BPJ approach, we are now developing a regional set of parameters for Missouri, Iowa, Nebraska and Kansas as an alternative approach to expand the utility of APEX to locations where data for full calibration are not available.

Technical Abstract: The Agricultural and Policy Environmental Extender (APEX) is capable of estimating edge-of-field water, nutrient, and sediment transport and is used to assess the environmental impacts of management practices. Current practice is to fully calibrate the model for each site simulation, which requires resources and data that are not always available. The objective of this study was to compare annual model performance for flow, sediment and phosphorus transport under two parameterization schemes: a best professional judgment (BPJ) parameterization based on readily available data and a fully calibrated parameterization based on site specific soil, weather, event flow and water quality data. The analysis was conducted using data from 19 sites at four different locations representing hydrologic conditions ranging from well to poorly drained soils and management systems covering row crop under different tillage systems and grazing systems. Regional model performance was based on the Nash Sutcliffe efficiency (NSE), the coefficient of determination (r2) and the regression slope between simulated and measured annualized loads for all site years. Although the BPJ model performance for flow was acceptable (NSE = 0.4), calibration improved it (NSE = 0.8). Acceptable simulation of sediment and total phosphorus transport (NSE = 0.3 and 0.8, respectively) was obtained only after full calibration at each site. Given the unacceptable performance of the BPJ approach, we are now developing a regional APEX parameterization as an alternative approach to expand the utility of APEX to locations where data for full calibration are not available.