Use of Physical Properties to Predict the Effects of Tillage Practices on Organic Matter Dynamics in Three Illinois Soils Gayoung Yoo,* Todd M. Nissen, and Michelle M. Wander ABSTRACT This work builds on a previous study of long-term tillage trials that found use of no-tillage (NT) practices increased soil organic carbon (SOC) sequestration at Monmouth, IL (silt loam soil) by increasing the soil’s protective capacity, but did not alter SOC storage in DeKalb, IL (silty clay loam), where higher clay contents provided a protec- tive capacity not affected by tillage. The least limiting water range (LLWR), a multi-factor index of structural quality, predicted observed soil CO 2 efflux patterns. Here we consider whether LLWR can predict sequestration trends at a third site, Perry, IL (silt loam soil) where SOC content is lower and bulk density is higher than in previously considered sites, and determine whether pore size characteristics can help explain the influence use of NT practices has had on SOC se- questration at all three locations. At Perry, LLWR was again related with differences in specific soil organic carbon mineralization rates (RESP sp ) (2000–2001). Reduced RESP sp rates explain increases in SOC storage under NT management observed only after 17 yr. Trends in RESP sp suggest use of NT practices only enhance physical protec- tion of SOC where soil bulk density is relatively high (approximately 1.4 g cm 23 ). In those soils (Monmouth and Perry), use of NT manage- ment reduced the volume of small macropores (15–150 mm) thought to be important for microbial activity. Physical properties appear to determine whether or not use of NT practices will enhance C storage by increasing physical protection of SOC. By refining the functions used to compute the LLWR and our understanding of the interac- tions between management, pore structure, and SOC mineralization, we should be able to predict the influence of tillage practices on SOC sequestration. D ESPITE MANY REPORTS that use of no-tillage (NT) practices sometimes fails to increase soil organic carbon (SOC) sequestration relative to conventionally tilled (CT) counterparts (Dick et al., 1991; Paustian et al., 1995; Angers et al., 1997; Needleman et al., 1999), efforts to understand why tillage impacts on SOC stor- age vary by sites are relatively rare. In many fine- textured soils, use of NT practices has increased SOC contents in the surface at the expense of SOC stored within the rooting zone (Wander et al., 1998; Kay and VandenBygaart, 2002). This observation is common especially when C inputs from crops are reduced under NT management as a result of lowered yield or when soil erosion is not a major concern (Hussain, 1997; Alvarez et al., 1998; Yang and Wander, 1999). When crop yield does not account for differences in the SOC content of soils maintained under NT and CT manage- ment, studies have considered the effects of tillage on SOC mineralization (Alvarez et al., 1995; Dick et al., 1991; Angers et al., 1997; Karunatilake et al., 2000). Tilled soils are generally reported to have greater CO 2 evolution rates than soils under NT management be- cause tillage modifies the decomposition environment by aerating the soil, breaking up soil aggregates, and incorporating residues into the soil profile (Beare et al., 1994; Fortin et al., 1996; Lee et al., 1996; Prior et al., 1997; Six et al., 2002). However, soil CO 2 evolution from the NT soils has been found to be equal to, or greater than, that from the CT soils during the growing season where the accumulation of SOC in the surface of NT soils has enhanced infiltration and water holding capac- ity (Blevins, 1984; Linn and Doran, 1984; Hendrix et al., 1988; Follett and Schimel, 1989; Alvarez et al., 1995; Franzluebbers et al., 1995). Specific carbon mineralization rates (RESP sp : CO 2 mineralized expressed per unit SOC) can be used to evaluate how readily SOC is mineralized. The quantity and quality of organic substrates and the surrounding environment will all influence this variable. Soil RESP sp has been used to predict the protective capacities of soils when the soils being compared have had similar con- tents of labile SOC (Franzluebbers and Arshad, 1997). Protective capacity has also been used to explain ele- vated RESP sp in soils where labile C stocks are relatively reduced. For example, Rice and Garcia (1994) observed higher RESP sp in soil obtained from a burned than from an unburned prairie. They associated lower RESP sp with greater physical protection of C in the unburned prairie and attributed this to structural integrity. Franzluebbers et al. (1995) observed higher RESP sp from a conven- tionally tilled soil than from a soil maintained under no-tillage management. Again, lower RESP sp was asso- ciated with greater physical protection of SOC. Soil RESP sp may be used as a tool to help predict SOC sequestration capacity. Yoo and Wander (2006) investi- gated two sites where the use of CT and NT practices for over a decade had previously been reported (Wander et al., 1998) to have had variable effects on SOC se- questration. In the site where use of NT management increased SOC contents relative to the CT treatment, sea- sonal mean SOC mineralization rate and RESP sp were greater from soils under CT than NT management. In the site where use of NT practices failed to increase SOC storage, there was no difference in mean SOC mineral- ization rate or RESP sp of the CT and NT treatments. G. Yoo, Korea Environment Institute, 613-2 Bulgwang-Dong, Eunpyeong- Gu, Seoul, 122-706 Korea. T.M. Nissen, Office of Multilateral Trade Affairs, Room 3828 HST, Department of State, Washington, DC 20520. M.M. Wander, Department of Natural Resources and Environmental Sciences, University of Illinois, S406 Turner Hall MC 047, 1102 South Goodwin Avenue, Urbana, IL 61801. Received 7 June 2005. *Corre- sponding author (gyyoo@kei.re.kr). Published in J. Environ. Qual. 35:1576–1583 (2006). Special Submissions doi:10.2134/jeq2005.0225 ª ASA, CSSA, SSSA 677 S. Segoe Rd., Madison, WI 53711 USA Abbreviations: CT, conventional tillage; LLWR, least limiting water range; NT, no tillage; RESP sp , specific soil organic carbon mineraliza- tion rate; SOC, soil organic carbon. Reproduced from Journal of Environmental Quality. Published by ASA, CSSA, and SSSA. All copyrights reserved. 1576 Published online July 6, 2006 Published online July, 2006