Deep soil carbon after 44 years of tillage and fertilizer management in southern Illinois compared to forest and restored prairie soils

No-till (NT) management can reduce soil erosion and increase soil carbon (C) in agricultural systems, but there is less certainty regarding deeper soil and how long-term tillage and fertilization practices compare to other land-use systems. The objective of this study was to quantify tillage and fertilizer management effects after 44 years (20 years in continuous corn [Zea mays L.] and 24 years in corn-soybean [Glycine max L.] rotation) on bulk density and soil C concentrations and stocks to a 1 m (3.3 ft) depth in a somewhat poorly drained Bethalto silt loam near Belleville, Illinois, and compare to nearby forest and restored prairie soils. Four tillage (moldboard plow, chisel tillage [ChT], alternate tillage, and NT) and five fertilizer (no fertilization control, nitrogen [N]-only, N + N-phosphorus-potassium [NPK] starter, NPK + NPKstarter, and NPK broadcast) treatments showed bulk density was lower in NT than moldboard plow treatments in 0 to 15 (0 to 6 in) and 25 to 50 cm (10 to 20 in) depths. Complete NPK treatments generally resulted in higher C stocks than N-only and control treatments from 0 to 25 cm (0 to 10 in), but no differences were detected from 25 to 100 cm (10 to 39 in) or 0 to 100 cm (0 to 39 in) due to fertilizer. No-till management increased C stocks compared to tillage treatments for 0 to 15 cm (0 to 6 in) and was greater than the ChT treatment for 0 to 100 cm (0 to 39 in). No-till/NPK maintained greater cumulative soil C stocks to 1 m than either undisturbed forest soils or restored prairie soils. Additionally, NT/NPK had the maximum soil C increase over time of 0.36 Mg C ha^-1 y^-1 (0.16 tn C ac^-1 yr^-1) for the top 15 cm (6 in) over 44 years.