Table 2.

Carbon debt payback times under different scenarios of conversion of Conservation Reserve Program (CRP) grassland to annual cropping systems at a site in southwest Michigan

	Carbon debt payback time: years
Agronomic management	Conventional tillage	Permanent no-till
Continuous corn	123 (43)	40 (11)
Corn–soybean rotation	89 (26)	29 (5)

The management system noted follows a first-year conversion of grassland to no-till soybeans as noted in Fig. 1. Projections are based on observations made during the establishment year plus projections of historical productivity and greenhouse gas fluxes from nearby sites under conventional tillage and permanent no-till rotations. Carbon debt payback times include coproduct offsets (SI Text). SEs (in parentheses) are based on the propagation of errors associated with the various components of carbon debt.