Photos: R.J. Kremer.

Soil Biological Health in Organic and Conventional Vegetable Production

Bob KremerUniversity of Missouri

kremerr@Missouri.edu

SOIL HEALTHComplex idea - many definitions are

proposed; it is “an evolving concept”

“Soil health focuses on the living, dynamic nature of soil that functions by incorporating the biological attributes of biodiversity, food web structure, ecosystem functioning and the intimate relationships of soil microorganisms with plants and animals” Kremer, 2016

Five Main Functions of Soil (All interactive):

Organic Matter Formation

Water Infiltration, Filtration, Storage

Atmosphere Modification (CO2, NxO, CH4 concentrations)

Habitat for Microorganisms

Medium for Plant Growth

Washington (Tokul ‘gravelly loam’)

Important biological attributes of �healthy soils�are influenced by vigorously growing plants

Soil Health Indicators:•Soil Microbial Diversity (Biodiversity)

•Soil Carbon Content & Quality -- Plant root contributions• (SOM ≈ 58% C)

Rhizobacteria on plant root surface metabolize plant-derived C and interact with plant.5000X magnification

Crimson clover provides Carbon and Nitrogen to soils

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Transformation of solar energy to available Carbon thru photosynthesis

Bacteria colonizing root surface = ‘rhizobacteria”

Metabolize exuded C Synthesize plant growth substances and aid soil structure

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Example of Structural Diversity:

Soil Microbial Diversity (Soil Biodiversity) - variety of living microorganisms at species, inter-species and intra-species levels in soil ecosystem- Key to soil functionality -• �Consortia� required to complete many biological processes

Fungi

Bacteria

Algae

Nematode

Earthworms

Bacteriophage (virus)

Bacteriophage (virus)

Bardgett,R.D. & W.H. van der Putten. 2014. Belowground biodiversity and ecosystem functioning. Nature 515:505-511.

Operational food webs are essential for optimum environmental functioning and “ecosystem services”

The Soil Food Web

Vulnerable to management

Soil Organic Matter (SOM) Components

Plant residues

Bacteria

Fungi Actinobacteria

SOM

CO2

Integration of biological structural diversity AND functional diversity

“SOM Quality” essential for adequate soil microbial diversity

High microbial diversity is critical:

Soluble OC“root exudates”

Involvement of “microbial consortia”

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MaizeHybrid

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“Conventional Management”SOC ≈ 12.5 g/kg soil

SOM = 2.18%

Organic Transition ManagementSOC ≈ 19.5 g/kg soil

SOM = 3.41%

Osage County, MO 2016Boone County, MO 2016

Active Carbon - Rhizosphere soils - V10 growth stageUp to 60% more AC in organically managed soils

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MC-1 MC-2

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Inorganic fertilizer

activity of microbial communities

Organic materials

N min

�. . . . . . chemical fertilizers may feed the plant, but organic fertilizers feed the soil.�Amy Stewart. 2004. The Earth Moved.

Deplete SOM(?)

Reduce fungi

Release P, S, K

Growth regulators

Mobilize Fe, Cu, Zn

Pathogen suppression

Stress tolerance

Improve soil health

Multifunctional Benefits of Organic Amendment

Potential losses

Physical Chemical

Biological

Soil Health is a Comprehensive Assessment Based on Sensitive Indicators Representing all Soil Properties

However, the complexity of soil hinders standardization of soil health measurements

• Bulk density*• Aggregate stability*• Pore size distribution

Water-filled pore space*• Water-holding capacity*• Water-infiltration rate• Soil compaction• Topsoil depth

“Tier 1 Soil Health Indicators”•Soil Organic Matter (C)*•Active C•Soil pH*•Electrical conductivity (EC)*•Cation excange capacity•Available P*•Exchangeable K*•Sodium absorption ratio*

• Microbial biomass C*• Microbial community structure (Biodiversity)• Microbial activity

Soil enzyme activity (i.e., glucosidase*)Soil respiration (Decomposition rate)

• Potentially mineralizable N (PMN)*• Soil disease suppressiveness• Nematode assessment• Earthworm assessment• Glomalin content

*Indicators typically used in soil health index models – datasets compiled for these indicatorsIndicators depicted as red font are measured frequently based on current large database

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Furthermore, Few Biological Indicators are included in Soil Health Tests- Minimal Routine Analyses and Difficulty for Field Measurement

Soil respiration (CO2 efflux) - indicator of biological activity (SQI 2001)Draeger Tube - color change shows relative amount CO2(appropriate conversion factor(s) allow calculation of soil microbial biomass C)

Microbial biomass => indicates potential ‘turnover’ rate relative to amount of N mineralized - tends to decline under degradation

Solvita “Soil Life Kit” - gel indicator color change (24-hr incubation),

qualitative indicator of respiration; expensive

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Dominant organisms in the soil with widely known importance are not considered in popular soil health assessment models

However, some commercial and government-supported labs are including selected microbial measurements in “Soil Health Testing Packages”

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Soil Microbial Community Structure, 2013 Organic Orchard Field StudyUsing Phospholipid Fatty Acid (PLFA) biochemical profiles (“fingerprints”)

Kremer ,Hezel, & Veum. 2015. Proc. Organic Agriculture Research Symposium (available at eOrganic.info)

Example of Soil Microbial Community (Microbiome) Assessment

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A New Paradigm for Soil Health Assessment

Adjustments to Soil Health Management based on “Soil Microbiome Analyses”

Foundation: The New Generation of Molecular Analysis Applied to Environmental Testing(Human Superorganism Microbiome Model – R. Dietert (2019)

Approaches:1. Taxonomic – measure microbial species & relative abundance based on species identification

2. Metagenomics – evaluate all microbial genes and abundance existing in soil (genomes of all species in soil representing functional properties)

3. Metabolomic – analysis or profile of all biochemicals the soil microbiome produces – a “fingerprint” of biochemicals in a given soil can inform functional capacity of that soil

This baseline information, collected using in-field DNA and biochemical detection kits, will be used to tailor treatments to adjust microbiome deficiencies caused by poor management or environmental conditions

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Microbiome Modification Strategies will be DevelopedUse of numerous soil health management approaches may be part of the strategy

Many scenarios are possible:- Microbiome shift or depletion might be restored using a cover crop rotation; or applying a

probiotic biostimulant- Stress conditions might be reduced or overcome by fortifying soil microbiome with stress-

tolerant microorganisms that promote function of critical, stress-susceptible microorganisms- Example: Under development of soil salinity problems, N-fixation in legume crops is reduced;

stress affecting the rhizobia is alleviated by prescribing a stress-tolerant plant growth-promoting rhizobacteria co-inoculated with the rhizobia, effective N-fixing root nodules are restored – Could be an interim adjustment until salinity is managed

- Co-inoculation can be a modification strategy for improving soil health and productivity

Forage legume –Saline soil control

Co-inoculation of Rhizobium + PGPR in high salt soil

Egamberdieva et al. 2013

Mycorrhizae soil health indicator Implications: Cover Crop System vs No Cover Crop

Faculty of Biology Genetics, University of Munich

Lehman et al., 2012

Increased AMF propagules specific for numerous crop host plants due to cover croppingThus cover crop management would score higher than no cover crops

Traditional management prescribed to adjust soil biological function:1. Cover crop mixes increase mycorrhizal species diversity for subsequent cash crop

Solar corridor planting arrangement set up for comparison with monoculture or “solid-planted” corn

Photo: R.J. Kremer.

Traditional management prescribed to adjust soil biological function:2. Intercropping for increasing soil microbial diversity and activity

3. Multiple beneficial functions of quality compost:Nutrient sourceSOM BuildupSource of biological activity

Kremer & Hezel. 2013. Soil quality improvement underan ecologically based farmingsystem in northwest Missouri. Renewable Agriculture and Food Systems 28:245– 254.

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The soil microbial community within organically managed systems may be more effective in mediating biological processes to achieve soil health and impact food production relative to non-organically managed sites.

It is likely that improved soil health contributes to higher quality foods compared with conventional counterparts.

*Correlation of soil health with fruit quality is a necessary next objective.References:Hezel & Kremer. 2008. Healing and building soil on

Prairie Birthday Farm. Missouri Prairie Journal 29 (3):14-20.

Kremer & Hezel. 2013. Soil quality improvement under an ecologically based farming system in northwest Missouri. Renewable Agriculture and Food Systems 28(3):245-254.

Kremer. 2014. Prairie soil health: a benchmark for better land management. Missouri Prairie Journal 35(3&4):17-19.

Kremer, Hezel & Veum. 2015. Ecologically-based management improves soil health in an organic orchard production system. Proceedings.OrganicAgriculture Research Symposium, pp. 1-4 (available at www.eOrganic)

MANAGEMENT KEYS FOR GOOD SOIL HEALTH

•REDUCE SOIL DISTURBANCE *•INCREASE PLANT DIVERSITY (Rotation, Perennial Crops)•CONTINUOUS LIVING ROOTS IN SOIL (As possible)•KEEP SOIL SURFACE COVERED AT ALL TIMES•BUILD SOIL ORGANIC MATTER• Crop Residue Management• Manure, Compost, Mulch, Biological products• Cover Crops• Integrated and Diversified Management

*Includes tillage, pesticide & inorganic fertilizer applications; drainage?

Summary

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Types and residence times of SOM components from plant and microbial cell residues

Source: Dohnalkova et al. 2017. Molecular and microscopic insights into the formation of soil organic matter in a red pine rhizosphere. Soils 2:4

Measurable soil health improvement -short term

Long-term contribution to soil health