soil structure and c sequestration under no tillage management

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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. - PowerPoint PPT Presentation

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  • Soil structure and C sequestration under no tillage managementGayoung Yoo* and Michelle M. WanderDepartment of Natural Resources and Environmental SciencesUniversity of Illinois

  • Variable no tillage influences by sitesNo 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.

  • BackgroundNo tillConventional till

  • SOIL STRUCTUREINPUTCrop yieldOUTPUTSoil erosionmicrobesSOCSoil waterSoil temp.

  • Soil structure and SOM dynamic models

  • WaterBalanceSubmodel

    ActiveSOM

    SlowSOM

    PassiveSOM

    Residues

    PlantGrowthSubmodel

    CO2

    CO2

    CO2

    CO2

    CO2

    SOMSubmodel

    Climate

    Soils

    Topography

    Management

    Century model

    f (sand)

    f (clay)

  • Site description DeKalbPoorly drainedDrummer silty clay loamMonmouthSomewhat poorly drainedMuscatine silt loamTreatmentsNT : no tillageCT : conventional tillageRandomized complete block design 3 blocks Fixed effect: site, till Random effect: year, date

  • ObjectivesInvestigate 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

  • Experimental methodsSoil CO2 efflux measurementLi 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 Means, estimated with least square means, within site or tillage not followed by the same letter were significantly different at P < 0.05.

    EffectSoil temp.-----oC------- SiteDeKalb18.85aMonmouth18.24a TillageNT18.54aCT18.55a

  • Correlation coefficients

    Soil tempSoil waterPRBDSpecific C min rates

    Soil temp10.03-0.010.310.27***Soil water1-0.19*-0.30*-0.34***PR10.30--0.06BD1-0.16Specific C min rates1

  • Development of Q10 equationBasic Q10 model with soil temperature and gravimetric water contentsSoil CO2 evolution = (b + r*SWC)*Q10 (Ts-10)/10

    R2 (validation)0.670.31

  • 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)

  • Least limiting water range(da Silva et al., 1994; Topp et al., 1994)Bulk density (g cm-3)1.11.5Volumetric water content (cm3 cm-3)0.20.5

  • The calculation of LLWR: Pedotransfer functions (da Silva and Kay, 1997)wetdry(1-Db/2.65) 0.1

  • Mean LLWRs

    wpsr

    0.347 c0.346 c0.353 c0.322 b

    0.212 b0.276 b0.196 a0.243 a

    LLWR

    0.032 a0.059 a

    0.083 b0.141 c

  • LLWR and SOC mineralization

  • Summary and ConclusionsInherently high protective capacity soilsHigh clay content, high SOC, high macroporosity, low BD, low LLWRNot likely to be affected much by practices that alter structure

    Intermediate protective capacity soilsMedium clay content, medium SOC, medium macroporosity, high BD and LLWRPhysical properties can be altered to affect biological activity and C sequestration by tillage practice

  • Acknowledgement

    I would also like to thank Todd Nissen, Vernica Rodrquez, 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.

    Today, I would like to share our efforts to investigate the soil structure and C sequestration under no tillage management. No tillage practice are widely believed to increase C sequestration by reducing SOM decay rates and reducing soil erosion. Iowa farm bureau assumes that fields converted to NT practice will sequester 0.5 to 1 ton of CO2/acre every year. This is despite the fact that many studies have found that use of NT practices does not increase SOC sequestration. Such findings are common for fine textured, poorly drained soil erosion particularly where erosion is not a major factoror where yields under NT have been reduced.This study was based on previous long-term research that reported that the use of NT practice for 10 years resulted in increase in SOC storage in one site, but not, in other sites. Here I show you results from a pair that we investigated in detail.This schematic summarized our thinking about controls over sequestration in our system.

    To explain the inconsistent tillage impact on SOC storage, we considered C balance between C inputs and outputs. We can assume inputs are equal since we know that there was no difference in average crop yield from 1989-2002 in NT or CT plots at either site. We also can assume soil erosion is negligible because fields were quite level. So, our efforts emphasized factors influencing SOC mineralization. Microbial C mineralization is primarily influenced by soil temperature and soil water content, both of which are under the influence of soil structure. Soil structure also influences the accessibility of C to microbes. Tillage practice influence SOC dynamics by modifying this soil structure through incorporating residues in the profile, breaking the aggregates, and aerating the soil.Despite its importance, soil structures influence on SOC turnover is not considered by most SOC dynamic models. Only information about primary particles, including sand and clay contents, are included as rate modifying factors. Our experiment has been conducted at two sites since 1985 where No tillage (NT) and conventional tillage, which includes moldborad and chisel plowing, are the main treatments.The trial is located at DeKalb where soil is poorly drained silty clay loam, and at Monmouth, where the soil is a somewhat poorly drained, silt loam. Randomized complete block design was used. Site and till are fixed effects and year and dates are random effects.This study has three objectives.Soil CO2 efflux was measured using Li Cor 6400 biweekly during the growing season before tillage in 2000, from planting to after tillage in 2001, and every two months from January to September in 2002.

    On the same dates of soil CO2 efflux measurement, soil temp, gravimetric water content, and penetration resistance in the depth of 0-30 cm were measured. Bulk density was measured two times per year right after planting and harvest. Soils used for pore size distribution were collected in the 0-30 cm as intact cores in spring before tillage, 2001. We used a modified suction plate method within the pressure range of 20 kPa ~ -1 kPa.

    Statistical analysis was performed using PROC mixed for ANOVA and Proc NLIN for non linear regression.

    We took the seasonal mean of C mineralization rate and results show that in DeKalb, there was no difference in mean CO2 evolution rate between NT and CT soils. In Monmouth, CT soil had significantly higher CO2 evolution rate compared to NT soil. These trends were consistent with SOC storage reported previously. Specific C mineralization rates, defined as mean C mineralization rate divided by SOC contents, provide information about the availability of SOC to microbes. We assume higher specific C min indicate low physical protection of SOC. Results show that specific C min rates were lower in DeKalb than in Monmouth, regardless of tillage practices. Whereas in Monmouth, SOC under the NT soil was more protected from decomposition compared to the CT soil. To follow up on this observation, we characterized site- and tillage-based effects on soil physical factors that might influence SOC mineralization patterns. For soil temperature, there was no significant effect of site or till. For soil water contents, DeKalb had significantly higher soil water content than Monmouth and there was no tillage influence on it. Monmouth had higher bulk density than DeKalb and soil under NT practice have higher bulk density at both sites. Penetration resistance was also higher under NT than CT treatments. Data of bulk density and penetration resistance imply that soils under NT treatment might have been compacted at both sites.

    Penetration resistance was higher in DeKalb than in Monmouth although bulk density was lower at DeKalb, indicating that this parameter is very dependent on soil texture and moisture.Using all 3 years data, we found that specific C min rates are positively correlated with soil temperature and negatively correlated with soil moisture. Negative correlation between soil water and C mineralization indicates that excess water limits SOC decomposition in our sites. Soil physical measure, bulk density and penetration resistance, was not directly related to C mineralization. Subsequent analysis focused on the interaction between soil water content and soil structure.

    To quantify the results from correlation, a basic Q10 equation was developed using nonlinear regression with data from the first two years, 2000 and 2001. These are the values for parameters; 63% of total variations in soil CO2 evolution rates could be explained by this Q10 model. Please note the relatively low degree of fit indicates that there are factors other than soil temp and moisture influencing C mineralization. Data from 2002 were used for validation of the developed Q10 equation. An interesting result from this analysis is the different explanatory power of this equation at DeKalb and Monmouth. The Q10 equation had higher explanatory power in DeKa

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