Modeling conservation practices in APEX: from the field to the watershed Wendy Francesconi a, ⁎, Douglas R. Smith b , Dennis C. Flanagan c , Chi-Hua Huang c , Xiuying Wang d a International Center for Tropical Agricuture (CIAT), Av. La Molina, 1581 La Molina, Lima, Peru b Grassland, Soil and Water Research Laboratory, 808 E Blackland Rd, Temple, TX 76502, USA c National Soil Erosion Research Laboratory, 275 S Russell Street, West Lafayette, IN 47907, USA d Texas A&M University, Blackland Research and Extension Center, Temple, TX 76502, USA abstract article info Article history: Received 1 June 2014 Accepted 21 April 2015 Available online 14 May 2015 Communicated by Joseph Makarewicz Index words: Lake Erie Best management practices Tile drainage Evaluation of USDA conservation programs are required as part of the Conservation Effects Assessment Project (CEAP). The Agricultural Policy/Environmental eXtender (APEX) model was applied to the St. Joseph River water- shed, one of CEAP's benchmark watersheds. Using a previously calibrated and validated APEX model, the simu- lation of various conservation practices (single and combined) was conducted at the field scale. Seven variables [runoff, sediment, total phosphorus (TP), dissolved reactive phosphorus (DRP), soluble nitrogen (SN), tile flow, and soluble nitrogen in tile (SN-Tile)], were compared between the simulated practices. The field-scale outputs were extrapolated to the areas encompassed by the different conservation practices at the watershed scale. The speculative estimations are presented as percentage reductions compared to the baseline scenario. When single conservation practices were implemented, reductions were 39% for sediment, 7% for TP, and 24% for SN-Tile. In contrast, losses of DRP and SN increased by 5% and 57%, respectively. When the conservation practices were combined, percentage reductions increased for all variables. The total reductions for combined two and three practices were 68% and 91% for sediments, 35% and 74% for TP, 1% and 48% for DRP, -43% and 28% for SN, and 50% and 85% for SN-Tile. Negative reductions were due to the slightly higher DRP and SN loads in no-till, mulch-till, and conservation crop rotation practices, and their greater extent of incorporation at the watershed scale. Overall, the cumulative and combined effects of field conservation practices can help address the watershed's excess nutrient and sediment concerns and improve water quality. © 2015 International Association for Great Lakes Research. Published by Elsevier B.V. All rights reserved. Introduction With the goal of improving water quality by reducing sediments, nu- trients and pesticides transported from agricultural fields, agricultural programs promote conservation practices [also referred to as Best Management Practices (BMPs)]. Conservation agricultural programs are designed by the United States Department of Agriculture, Natural Resources Conservation Service (USDA-NRCS), and implemented through local Soil and Water Conservation Districts (SWCDs). Driven by public concerns of nonpoint source environmental and water quality degradation, several conservation programs have been developed as a consequence of additional funding stipulated in the 2002 Farm Bill. To evaluate the environmental impact of such programs at the watershed scale, the Conservation Effects Assessment Project (CEAP) was established (Richardson et al., 2008). Within CEAP's Watershed Assess- ment Studies, the St. Joseph River watershed in northeastern Indiana has been targeted by the Agricultural Research Service (ARS) to provide information on the environmental effects of conservation practices. So far, the evaluation of a few conservation practices at the field scale has been completed for this watershed (Francesconi et al., 2014; Smith et al., 2008, 2015a,2015b; Pappas et al., 2008). However, more research is required on the impact of single and combined conservation practices at the field and the watershed scale. Monitoring and modeling the potential benefits of conservation prac- tices at the watershed scale is challenging (Tomer and Locke, 2011). While monitoring provides empirical data, it is also time consuming and costly which limits the number of practices to be evaluated. On the other hand, modeling can simulate multiple conservation practices. However, modeling of large watersheds makes the evaluation of distinct conservation practices difficult, as landscape components are merged into single units (e.g., hydrologic response units in the Soil and Water As- sessment Tool — SWAT) (O'Donnell, 2010). Furthermore, detailed man- agement information of agricultural practices at the watershed scale is difficult to collect, and several years of monitoring data are usually re- quired for the modeling analyses to be robust. So far, various studies have been conducted to provide some accountability for the incorpora- tion of conservation practices at CEAP's targeted watersheds. The review by Richardson et al. (2008) summarizes some of these findings. Among them, monitoring results have shown the significant benefits of Conser- vation Reserve Programs (CRP), fertilizer management techniques, re- duced tillage, and wetlands for mitigating sediment and nutrient Journal of Great Lakes Research 41 (2015) 760–769 ⁎ Corresponding author. Tel.: +51 1 349 2273x112. E-mail address: W.Francesconi@cgiar.org (W. Francesconi). http://dx.doi.org/10.1016/j.jglr.2015.05.001 0380-1330/© 2015 International Association for Great Lakes Research. Published by Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Journal of Great Lakes Research journal homepage: www.elsevier.com/locate/jglr