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

Variable no tillage influences by sites No tillage (NT) does not always increase C sequestration. – Soils are fine textured and poorly drained where soil erosion is not a major factor or yield under NT is reduced.

Background Wander et al., 1998 No till Conventional till

SOIL STRUCTURE INPUT Crop yield Soil CO 2 efflux OUTPUT Soil erosion microbes SOC Soil water Soil temp. Tillage

Soil structure and SOM dynamic models

Site description DeKalb Poorly drained Drummer silty clay loam Monmouth Somewhat poorly drained Muscatine silt loam Treatments NT : no tillage CT : conventional tillage Randomized complete block design - 3 blocks - Fixed effect: site, till - Random effect: year, date

Objectives Investigate soil CO 2 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

Experimental methods Soil CO 2 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)

Seasonal mean and specific C mineralization

Soil physical parameters Soil water -----% b 22.86a 24.30a 23.6a Bulk density ---g cm a 1.39b 1.41b 1.31a † Means, estimated with least square means, within site or tillage not followed by the same letter were significantly different at P < Effect Soil temp o C SiteDeKalb18.85a Monmouth18.24a TillageNT18.54a CT18.55a Penetration resistance -- blows m b 58.83a b 59.97a

Correlation coefficients Soil temp Soil water PRBD Specific C min rates Soil temp *** Soil water1-0.19*-0.30*-0.34*** PR BD Specific C min rates 1

Development of Q 10 equation Basic Q10 model with soil temperature and gravimetric water contents – Soil CO 2 evolution = (b + r*SWC)*Q10 (Ts-10)/10 SiteQ 10 brR2R2 DeKalb Monmouth R 2 (validation)

Pore size distribution † Least square means within site not followed by the same letter were significantly different at P < Nissen et al. (unpublished data) Total poreMacropore (> 30 um) Micropore ( < 30 um) ml g -1 soil DeKalbNT0.444 a0.104 a0.334 a CT0.442 a0.109 a0.340 a MonmouthNT0.339 a0.068 a0.271 a CT0.379 b b0.294 a A B A B A B

Least limiting water range (da Silva et al., 1994; Topp et al., 1994) θ fc Field capacity at Mpa (Haise et al., 1955) θ afp Air-filled porosity of 10 % (Grable and Siemer, 1968) θ sr Soil resistance of 2 Mpa (Taylor et al., 1966) θ wp Wilting point at -1.5 Mpa (Richards and Weaver, 1944) Bulk density (g cm -3 ) Volumetric water content (cm 3 cm -3 ) LLWR

The calculation of LLWR: Pedotransfer functions (da Silva and Kay, 1997) LimitsFunctionsData input θ fc SOC, clay, bulk density θ afp bulk density θ wp SOC, clay, bulk density θ sr SOC, clay, bulk density wet dry (1-D b /2.65) – 0.1

Mean LLWRs SiteTillθ fc θ afp cm 3 cm DeKalb NT0.541 c0.379 b CT0.560 d0.412 a Monmouth NT0.427 b0.360 a CT0.411 a0.384 a Wet limit Dry limit θ wp θ sr c0.346 c c0.322 b b0.276 b a0.243 a LLWR a a b c

LLWR and SOC mineralization

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

Acknowledgement I would also like to thank Todd Nissen, Ver ó nica Rodr í quez, 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.