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ARS Home » Midwest Area » Ames, Iowa » National Laboratory for Agriculture and The Environment » Agroecosystems Management Research » Research » Publications at this Location » Publication #430447
Research Project: Sustainable Intensification in Agricultural Watersheds through Optimized Management and Technology

Location: Agroecosystems Management Research

Title: Modeling nitrogen fluxes in a tile-drained cropping system in the midwest using an enhanced SWAT

Author
item SHAHID, MUHAMMAD RIZWAN - Iowa State University
item QI, JUNYU - University Of Maryland
item Emmett, Bryan
item Malone, Robert
item Rogovska, Natalia
item O'Brien, Peter
item Kovar, John
item Radke, Anna
item Feyereisen, Gary
item King, Kevin

Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/28/2026
Publication Date: N/A
Citation: N/A

Interpretive Summary: Corn and soybean production in the humid poorly drained Midwest U.S. is paramount on artificial (tile) drainage and crop production practices such as fertility management. Fertilizer, specifically nitrogen, costs are one of the greatest expenditures in crop production agriculture. Enhancing nitrogen use efficiency and preventing nitrogen loss is a focus of many conservation management practices. The Soil and Water Assessment Tool (SWAT) model was integrated with a new carbon/nitrogen component and shown to capture the uncertainty associated with measured nitrogen fluxes in artificially drained corn-soybean systems with and without cover crops. These findings are important to practitioners, extension specialists, conservationists, and policy makers investigating and promoting economically feasible agricultural management practices that increase nitrogen use efficiency in the Midwestern U.S., thus improving production profitability.

Technical Abstract: Artificial (tile) drainage systems are extensively implemented across the U.S. Midwest to enhance crop production in poorly drained soils; however, they also pose environmental challenges by significantly altering nitrogen fluxes within agricultural landscapes. In response, sustainable intensification strategies seek to increase agricultural productivity while reducing environmental impacts, often through improved management practices such as cover cropping and conservation tillage. Effectively evaluating the trade-offs and synergies of agricultural management practices demands advanced modeling tools capable of representing coupled biogeochemical and hydrological processes across diverse spatial and temporal scales. This study presents the first application of an enhanced version of the Soil and Water Assessment Tool (SWAT), integrated with Century/DayCent-based biogeochemical modules, to simulate both nitrate (NO3') loss and nitrous oxide (N2O) fluxes in a tile-drained corn–soybean system. The model was applied to long-term field data (2004–2010) from an Iowa site with two treatments: with and without winter rye cover crops. With careful calibration, the model closely matched observed crop yields, tile discharge volumes, NO3' drainage losses, and N2O fluxes under both winter rye cover crop and no-cover scenarios. The model simulated a ~41% reduction in NO3' leaching with cover crops, close to the observed ~50%. In contrast, effects on N2O flux varied by year and conditions, ranging from -30% to 67% (observed: -24% to 28%). Overall, the enhanced SWAT model demonstrates promise for assessing nitrogen dynamics and conservation practices in tile-drained agroecosystems. However, further refinement is required to improve the simulation of daily N2O fluxes and the complex interactions associated with cover cropping.