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Evaluation of the APEX Model to Simulate Runoff Quality from Agricultural Fields in the Southern Region of the United States
Author(s) -
RamirezAvila John J.,
Radcliffe David E.,
Osmond Deanna,
Bolster Carl,
Sharpley Andrew,
OrtegaAchury Sandra L.,
Forsberg Adam,
Oldham J. Larry
Publication year - 2017
Publication title -
journal of environmental quality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.888
H-Index - 171
eISSN - 1537-2537
pISSN - 0047-2425
DOI - 10.2134/jeq2017.07.0258
Subject(s) - surface runoff , agriculture , apex (geometry) , environmental science , hydrology (agriculture) , water quality , geography , geology , ecology , archaeology , mathematics , geometry , geotechnical engineering , biology
The Agricultural Policy Environmental eXtender (APEX) model has been widely applied to assess phosphorus (P) loss in runoff water and has been proposed as a model to support practical decisions regarding agricultural P management, as well as a model to evaluate tools such as the P Index. The aim of this study is to evaluate the performance of APEX to simulate P losses from agricultural systems to determine its potential use for refinement or replacement of the P Index in the southern region of the United States. Uncalibrated and calibrated APEX model predictions were compared against measured water quality data from row crop fields in North Carolina and Mississippi and pasture fields in Arkansas and Georgia. Calibrated models satisfactorily predicted event‐based surface runoff volumes at all sites (Nash‐Sutcliffe efficiency [NSE] > 0.47, |percent bias [PBIAS]| < 34) except Arkansas (NSE < 0.11, |PBIAS| < 50) but did not satisfactory simulate sediment, dissolved P, or total P losses in runoff water. The APEX model tended to underestimate dissolved and total P losses from fields where manure was surface applied. The model also overestimated sediments and total P loads during irrigation events. We conclude that the capability of APEX to predict sediment and P losses is limited, and consequently so is the potential for using APEX to make P management recommendations to improve P Indices in the southern United States. Core Ideas Calibrated APEX reasonably predicted runoff in no‐tillage and conventional tillage fields. APEX was unsatisfactory in predicting sediment losses, especially from pasture fields. P loss was inadequately predicted, especially in fields with surface applied manure. Adding a surface manure P pool to APEX could improve P model predictions. Improving P model predictions allow it to be used to refine southern region P Indices.