405 JULY/AUGUST 2017—VOL. 72, NO. 4 JOURNAL OF SOIL AND WATER CONSERVATION Maninder K. Walia is a postdoctoral fellow in the Department of Agronomy and Plant Genetics at the University of Minnesota, Morris, Minnesota. Sara G. Baer is a professor in the Department of Plant Biology and Center for Ecology at South- ern Illinois University, Carbondale, Illinois. Ron Krausz is a director at Belleville Research Center in the Department of Plant, Soil, and Agricul- tural Systems at Southern Illinois University, Carbondale, Illinois. Rachel L. Cook is an assis- tant professor in the Department of Forestry and Environmental Resources at North Carolina State University, Raleigh, North Carolina. Deep soil carbon after 44 years of tillage and fertilizer management in southern Illinois compared to forest and restored prairie soils M.K. Walia, S.G. Baer, R. Krausz, and R.L. Cook Abstract: 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 + NPK starter , 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. Key words: bulk density—carbon stocks—fertilizer—forest soils—prairie restored soils—tillage Since the 1960s, no-till (NT) systems have been shown to be effective in the mid- western Corn Belt for corn (Zea mays L.) and soybean (Glycine max L.) production, soil moisture conservation, and soil loss reduction (Moody et al. 1961; Triplett Jr. et al. 1963, 1968; Free at al. 1963; Pimentel et al. 1995; Derpsch 1998). No-till sys- tems in agriculture have also been proposed as an alternative to replace intensive tillage systems to sequester soil carbon (C) and to improve soil properties (Blanco-Canqui et al. 2009; Ogle et al. 2012). Soils under NT remain undisturbed and crop residue remains on the soil surface increasing soil organic matter, thus encouraging C accumulation, conserving soil moisture, and allowing for establishment of subsurface macro- and micropores (Dao 1996; Deen and Kataki 2003; Olson et al. 2005; Grandy et al. 2006; Gál et al. 2007; Ussiri and Lal 2009), stable aggregate formation (So et al. 2009; Kumar et al. 2012a), and greater soil quality indi- ces like microbial and earthworm activity (Karlen et al. 1994). Tillage has been attributed as the pri- mary cause of soil C oxidation and emission of carbon dioxide (CO 2 ) (Reicosky and Lindstrom 1993; Reicosky 1997; Al-Kaisi and Yin 2005). Kern and Johnson (1993) estimated historical soil C losses of 16% in the top 30 cm (12 in) after cultivation for major field crops in the contiguous United States. Conversion to NT has potential for soil C sequestration (Lal et al. 1998; Liebig et al. 2005; Franzluebbers 2005; Franzluebbers and Follett 2005; Kumar et al. 2012b). Based on 67 long-term experiments across the globe, conversion of a conventional tillage system to NT could result in a 0.57 ± 0.14 Mg C ha –1 y –1 (0.25 ± 0.063 tn C ac –1 yr –1 ) sequestration rate in top 30 cm (12 in) soil depth (West and Post 2002), but NT affects both the concentration and the distribution of soil C within the soil profile (Sundermeier et al. 2005; Ogle et al. 2012). A meta-analysis of 69 paired experiments showed overall that conversion from conventional tillage to NT changes the distribution of soil C, but not necessarily the total amount down to 40 cm (15.7 in) (Luo et al. 2010). Fertilization additions can also lead to increases in soil C content (Rasmussen et al. 1980; Janzen 1987; Glendining and Powlson 1991; VandenBygaart et al. 2003), but responses of nitrogen (N) fertilization on soil C are highly variable (Campbell et al. 1991; Janzen et al. 1998; Khan et al. 2007). Neff et al. (2002) showed that N additions accel- erated decomposition of the light fraction of soil C, but tended to further stabilize soil in heavier fractions. Campbell and Zentner (1993) reported that to maintain soil organic matter, apart from controlling soil erosion, sufficient N must be applied to the system to compensate for that removed in the grain. Conversion of agricultural land into native vegetation (forests or prairies) is often cited as an effective means to restore soil C (Post and Kwon 2000; Conant et al. 2001). Martens et al. (2003) suggested that conver- sion of former agricultural land to pasture and forest ecosystems is an option for mit- igation of increased atmospheric CO 2 based on a 130-year study showing that forest and pasture land use significantly retained more soil C than cropping systems by 46% and 25%, respectively. In contrast, the study con- ducted in Wisconsin found that the annual average soil organic C (SOC) sequestration doi:10.2489/jswc.72.4.405 Copyright © 2017 Soil and Water Conservation Society. All rights reserved. www.swcs.org 72(4):405-415 Journal of Soil and Water Conservation