Replacing Corn on Sloping Farmland by Bioenergy Crops With Optimized Harvest Frequencies: Implications for Soil and Water Conservation and Biofuel Production

Abstract

The promise of bioenergy crops includes their high productivity, suitability for marginal land, and environmentally friendly effects. Utilizing a previously calibrated Soil and Water Assessment Tool model, the effects of replacing corn with perennial bioenergy crops of Alamo switchgrass (Panicum virgatum L.) and Miscanthus × giganteus on soil erosion, biomass yield, and biofuel production potential were analyzed with varying slope gradients (0%–2%, 2%–4%, and >4%) over a 35-year period (1984–2018) across 14 zones of the Upper Mississippi River Basin (UMRB). Simulated results showed that the average annual soil erosion increased from upstream to downstream zones across the UMRB. Notably, Miscanthus produced approximately twice as much biomass as switchgrass in upstream zones with higher latitudes, with these differences diminishing in downstream zones due to their temperature preference. The single-harvest scenario for switchgrass annually in all 14 zones and the two-harvest scenario for Miscanthus in upstream Zones A–G and single-harvest scenario for downstream Zones H–N were identified as the optimal harvest frequencies. In contrast to corn land use, switchgrass and Miscanthus reduced soil erosion by more than 90% for the selected high-risk slope gradients under the optimized harvest frequencies. Furthermore, both Miscanthus and switchgrass substantially reduced organic N, nitrate N, and total N losses across all zones. Among these optimized scenarios, Miscanthus emerged as a better alternative to corn for selected sloping farmland, owing to its superior biofuel production (9,101 L ha⁻¹) and total biofuel price (4.16 billion US$). These findings provide insights into transitioning from corn to perennial bioenergy crops in the sloping farmland of the U.S. Corn Belt, promoting sustainable biofuel production while mitigating environmental burdens.