Ziyi Li

Ph.D. Level Student
University of Illinois Urbana-Champaign
Advised by Dr. Kaiyu Guan

Assessing the Impacts of Crop Rotations on Crop Productivity and Environmental Sustainability in the U.S. Midwest

Corn and soybean have predominantly been cultivated in rotation in the U.S. Midwest, with the remaining corn grown as continuous monoculture. The corn-soybean rotation (CS) is widely recognized for its benefits in improving corn and soybean yield compared with continuous-cropping (CC) systems. However, the underlying mechanisms of how crop rotation and nitrogen (N) fertilizer application on agroecosystem carbon (C) and N dynamics are not fully understood. In this study, we utilized the advanced agroecosystem model, ecosys, to evaluate the impacts of CS on soil inorganic nitrogen (SIN) and soil organic carbon (SOC) dynamics compared with CC. We first validated ecosys using extensive N fertilizer trial data collated from seven Illinois sites from 1999 to 2008, as well as carbon and energy fluxes data of three flux tower sites in Illinois from 2021 to 2022. The model’s performance demonstrated ecosys’ ability to accurately capture N fertilizer-yield responses and daily net ecosystem exchange (NEE) under different rotation systems. We then extended the simulations in those seven Illinois sites to 2022 and assessed the integrated outcomes of different rotation systems based on the seven site simulations during 1999-2022. We found that: (1) soybean leaves less residue but has a higher residual N/C than corn, resulting in increased early-season soil temperature and organic N contents in the subsequent corn year. Both of these factors enhance soil mineralization and N uptake, thereby contributing to higher corn yield in CS relative to CC systems. The corn yield benefits of CS compared with CC can be compensated by adding more N fertilizer in the corn year. (2) Although the CS produced less GPP, further resulting in a reduction in long-term SOC compared with CC, it improved environmental sustainability by reducing N leaching, N2O, and NH3 emissions. (3) CS outperforms CC under higher fertilizer/corn price ratio, soybean/corn price ratio, and corn price, also the relative agronomic benefits will decrease with higher fertilizer rate. Our findings provide essential insights for understanding both the economic and environmental benefits of adopting corn-soybean rotations in the U.S. Midwestern agroecosystems.