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ARS Home » Northeast Area » Beltsville, Maryland (BARC) » Beltsville Agricultural Research Center » Adaptive Cropping Systems Laboratory » Research » Publications at this Location » Publication #332282
Title: Evaluation of the agricultural policy environmental extender (APEX) for the Chesapeake Bay Watershed

Author
item Timlin, Dennis
item CHUN, JONG-AHN - Korea University
item Meisinger, John
item KANG, KWANGMIN - University Of Maryland
item Fleisher, David
item STAVER, KEN - University Of Maryland
item Daughtry, Craig
item Russ, Andrew - Andy

Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/28/2019
Publication Date: 5/30/2019
Citation: Kang, K., Timlin, D.J., Meisinger, J.J., Daughtry, C.S., Russ, A.L., Fleisher, D.H., Jeong, J., Staver, K. 2019. Evaluation of the agricultural policy environmental extender (APEX) for the Chesapeake Bay Watershed. Agricultural Water Management. 221:477-485.

Interpretive Summary: The Agricultural Policy Extender Model (APEX) is a farm scale model and simulates interactions between agricultural management practices and ecosystem processes important to conservation efforts including nutrient and soil transport, soil water balances, pesticides and crop growth. This model has been used to evaluate the effects of cropland management practices on water quality within the Chesapeake Bay Watershed. The simulation results of models such as APEX can be somewhat uncertain since it is impossible to calibrate the model and completely characterize all the environmental and biological properties that affect simulation results. We tested APEX to see how well it could predict observed values of corn yields and soil water content measured in a small watershed located in the larger Chesapeake Bay region without additional calibration of model parameters. The model predicted the observed data well using parameters provided with the model by the developers and researchers employing it for use in the Chesapeake Bay watershed. The results of this study provides additional confidence that the APEX model can realistically represent crop and soil processes in the Chesapeake Bay Watershed. This information will be of interest to scientists, agricultural managers and policy analysists interested in understanding how agricultural practices impact the environment and agricultural productivity.

Technical Abstract: The Agricultural Policy/Environmental Extender (APEX) is a complex mechanistic simulation model designed to evaluate agricultural management strategies and effects on yields, water and soil quality, and resource use. It is one of the main models used in the Conservation Effects Assessment Project (CEAP) assessment program and has been employed to evaluate the effects of conservation practices in the Chesapeake Bay Watershed (CBW). APEX is normally parameterized for each application using selected datasets from the region. The application area is usually very large and not all areas may be represented by the calibration. Additional tests of the model can improve confidence in the results. The objective of this study is to evaluate the performance of APEX for corn yields and water balance using current parameters developed for the CBW. This study used observations from the OPE-3 site (Optimizing Production Inputs for Economic and Environmental Enhancement) which located at the US Department of Agriculture, Henry A. Wallace Agricultural Research Center, Beltsville, Maryland, USA. Data from the OPE-3 site consists of water content at various layers, corn yields, and ET covering the period from 1998 to 2013. The results for total water in the soil profile (to 100 cm) showed that simulated water amounts were about 4.4 cm higher than observed, but the trends were very similar to observed. The statistical error analysis of R-square, Nash-Sutcliffe (NS) efficiency coefficient and Root Mean Square Error (RMSE) are 0.59, 0.51 and 0.21 cm/day, respectively. Simulated yields were 4.6 t/ha lower than measured, but the trends were also very similar to measured. APEX estimation of ET looks reasonable trend to observed ET in OPE-3 site; the model R-square, NS and RMSE are 0.56, 0.41 and 4.49 mm/month, respectively. The results of this study showed that model performance of yield estimation and water balance was acceptable when using datasets for which no calibration was carried out.