|Sadler, Edward - John|
|Sudduth, Kenneth - Ken|
|Lerch, Robert - Bob|
Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/5/2011
Publication Date: 7/1/2012
Citation: Mugdal, A., Baffaut, C., Anderson, S.H., Sadler, E.J., Kitchen, N.R., Sudduth, K.A., Lerch, R.N. 2012. Using APEX to develop and validate physically-based indices for the delineation of critical management areas. Journal of Soil and Water Conservation. 67: 284-299. Interpretive Summary: Finding areas within a field that require special management because of their risk to water quality, also called critical management areas, is essential to maximize grain production and minimize environmental impacts. In this study, an index was proposed to identify these areas in a corn-soybean field characterized by a claypan, a restrictive clay layer occurring 3 to 20 inches below ground surface, and for which water quality and crop yield data were available from 1991 to 2002. A computer simulation model was used to provide estimates of crop yields and runoff as well as sediment and atrazine losses within the field. Two indices were proposed that use readily available soil and landscape parameters. These index values correlated well with measured crop yields as well as simulated crop yields and runoff, sediment loss and atrazine loss obtained from the model. Critical management areas were identified from these index values and from the model results. The indices captured 100 % of the runoff and sediment and 60 % of the atrazine critical areas identified with the simulation model. These critical areas also matched lower corn productivity areas. Management scenarios were simulated that differentiated the management of the critical areas from the rest of the field. Indices such as these for identifying areas of higher environmental risk and lower productivity could provide objective criteria for effective targeting of best management practices.
Technical Abstract: Targeting critical management areas (CMAs) within cropped fields is essential to maximize production while implementing alternative management practices that will minimize impacts on water quality. The objective of this study was to develop a physically-based index to identify CMAs in a 32-ha (79-ac) field characterized by a claypan, a restrictive clay layer occurring within the upper 30 to 50 cm (12 to 20 in), and under a corn-soybean crop rotation since 1991. Thirty-five subareas were defined based on slope, claypan depth, and soil mapping units. The Agricultural Policy/Environmental eXtender (APEX) model was calibrated and validated from 1993 to 2002 for runoff, sediment and atrazine loads measured at the outlet and crop yields throughout the field. Correlation analysis was performed between simulated output by subarea and physical parameters including claypan depth (CD), surface saturated hydraulic conductivity (Ksat) and subarea slope (SL). Two indices were developed, the Conductivity Claypan Index (CCI; CD*Ksat /SL), and the Claypan Index (CPI; CD/SL) that correlated with simulated crop yields, runoff, atrazine, and sediment loads. Together, these indices captured 100 % of CMAs for simulated runoff and sediment yield, and 60 % of CMAs for simulated atrazine in surface runoff, as predicted by APEX. These critical areas also matched lower corn productivity areas. Management scenarios were simulated that differentiated the management of the CMAs from the rest of the field. Indices such as these for identifying areas of higher environmental risk and lower productivity could provide objective criteria for effective targeting of best management practices.