Data from: Carbon debt of Conservation Reserve Program (CRP) grasslands converted to bioenergy production

Over 13 million ha of former cropland are enrolled in the US Conservation
Reserve Program (CRP), providing well-recognized biodiversity, water
quality, and carbon (C) sequestration benefits that could be lost on
conversion back to agricultural production. Here we provide measurements
of the greenhouse gas consequences of converting CRP land to continuous
corn, corn–soybean, or perennial grass for biofuel production. No-till
soybeans preceded the annual crops and created an initial carbon debt of
10.6 Mg CO2 equivalents (CO2e)·ha−1 that included agronomic inputs,
changes in C stocks, altered N2O and CH4 fluxes, and foregone C
sequestration less a fossil fuel offset credit. Total debt, which includes
future debt created by additional changes in soil C stocks and the loss of
substantial future soil C sequestration, can be constrained to 68 Mg
CO2e·ha−1 if subsequent crops are under permanent no-till management. If
tilled, however, total debt triples to 222 Mg CO2e·ha−1 on account of
further soil C loss. Projected C debt repayment periods under no-till
management range from 29 to 40 y for corn–soybean and continuous corn,
respectively. Under conventional tillage repayment periods are three times
longer, from 89 to 123 y, respectively. Alternatively, the direct use of
existing CRP grasslands for cellulosic feedstock production would avoid C
debt entirely and provide modest climate change mitigation immediately.
Incentives for permanent no till and especially permission to harvest CRP
biomass for cellulosic biofuel would help to blunt the climate impact of
future CRP conversion.