Perennial Bioenergy Grasses Begin Rebuilding Midwest Soil Carbon Lost to Maize

Nearly two centuries of maize-based agriculture in the U.S. Midwest has halved soil organic carbon (SOC) stocks compared with tallgrass prairies native to the region. Replacing annual maize/soy cropping with perennial bioenergy grasses may partially reverse these resulting SOC deficits.

A recent Center for Advanced Bioenergy and Bioproducts Innovation (CABBI) study explored the ability of perennial bioenergy crops to restore agricultural soils to pre-cultivation prairie conditions by comparing SOC under perennial bioenergy crops planted on former corn/soy fields with maize-based annual cropping and native prairie. The study is published in the journal Geoderma.

Researchers quantified SOC stocks by depth to 1 m among native remnant prairie, maize cropping systems, and seven recently (<11 years) established perennial bioenergy cropping systems (miscanthus and switchgrass) across Illinois. They then quantified SOC stock change after five years in miscanthus and switchgrass and used carbon isotopes (δ¹³C) to determine the origin of new C entering the soil.

Across sites, average SOC stocks to 1 m depth on an equivalent soil-mass basis were 146 Mg C ha^-1 (prairie), 107 Mg C ha^-1 (miscanthus), 97.9 Mg C ha^-1 (switchgrass), and 87.7 Mg C ha^-1 (maize). SOC increased in the first five years under mature bioenergy crops at four of seven sites. δ¹³C analyses of surface depths confirmed that SOC increases were derived from miscanthus and switchgrass.

This work demonstrates the potential of perennial bioenergy crops to rebuild SOC over time, even with annual harvesting, and address the SOC deficit caused by annual maize cropping.