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1	Soil structure and C sequestration under no tillage management Gayoung Yoo* and Michelle M. Wander Department of Natural Resources and Environmental Sciences University of Illinois
2	Variable no tillage influences by sites No tillage (NT) does not always increase C sequestration.
3	Background
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5	Soil structure and SOM dynamic models
6	Site description
7	Objectives Investigate soil CO₂ evolution patterns where tillage practices have had varied influences on SOC Characterize site- and treatment-based differences in soil physical factors that might control C dynamics Determine whether the soil structural quality explains differences in SOC mineralization
8	Experimental methods Soil CO₂ efflux measurement Li Cor 6400 (from 2000 to 2002) Environmental variables Soil temperature, soil moisture, penetration resistance (PR), bulk density, and pore size distribution Statistical method ANOVA using PROC MIXED Non-linear regression using PROC NLIN (SAS Institute)
9	Seasonal mean and specific C mineralization
10	Soil physical parameters
11	Correlation coefficients
12	Development of Q10 equation Basic Q10 model with soil temperature and gravimetric water contents Soil CO₂ evolution = (b + rSWC)Q10 ^(Ts-10)/10
13	Pore size distribution
14	Least limiting water range (da Silva et al., 1994; Topp et al., 1994)
15	The calculation of LLWR: Pedotransfer functions (da Silva and Kay, 1997)
16	Mean LLWRs
17	LLWR and SOC mineralization
18	Summary and Conclusions Inherently high protective capacity soils High clay content, high SOC, high macroporosity, low BD, low LLWR Not likely to be affected much by practices that alter structure Intermediate protective capacity soils Medium clay content, medium SOC, medium macroporosity, high BD and LLWR Physical properties can be altered to affect biological activity and C sequestration by tillage practice
19	Acknowledgement I would also like to thank Todd Nissen, Verónica Rodríquez, Inigo Virto, and Iosu Garcia for their invaluable assistance in the field. Special thanks to Emily Marriott, Ariane Peralta, and Carmen Ugarte for their helpful discussion, editing, and advice.