Soil structure and C sequestration under no tillage management

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. • Soils are fine textured and poorly drained where soil erosion is not a major factor or yield under NT is reduced.

3. Wander et al., 1998 Background No till Conventional till

4. Soil CO2 efflux Tillage OUTPUT Soil erosion INPUT Crop yield SOC microbes Soil temp. Soil water SOIL STRUCTURE

5. Soil structure and SOM dynamic models

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

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 † Means, estimated with least square means, within site or tillage not followed by the same letter were significantly different at P < 0.05.

11. Correlation coefficients

12. Development of Q10 equation • Basic Q10 model with soil temperature and gravimetric water contents • Soil CO2 evolution = (b + r*SWC)*Q10 (Ts-10)/10

13. A A A B B B Pore size distribution † Least square means within site not followed by the same letter were significantly different at P < 0.05. Nissen et al. (unpublished data)

14. θfc Field capacity at -0.01 Mpa (Haise et al., 1955) LLWR θsrSoil resistance of 2 Mpa (Taylor et al., 1966) 0.1 0.5 θafpAir-filled porosity of 10 % (Grable and Siemer, 1968) θwpWilting point at -1.5 Mpa (Richards and Weaver, 1944) Least limiting water range(da Silva et al., 1994; Topp et al., 1994) 0.5 Volumetric water content (cm3 cm-3) 0.2 1.1 1.5 Bulk density (g cm-3)

15. The calculation of LLWR: Pedotransfer functions (da Silva and Kay, 1997) wet (1-Db/2.65) – 0.1 dry

16. Wet limit Dry limit 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.