Cover crop screening trials - Bradford Farm - 1997

Soil Health Impacts of Cover CropsBob Kremer & Kristen Veum

USDA-ARS & University of Missouri

AcknowledgmentsUniversity of Missouri Soil Health Lab

Dr. David HammerDr. Russ DresbachDonna Brandt

University of Missouri Bradford Research & Extension Center

Tim ReinbottKerry Clark

Missouri USDA-NRCS Soil Health Team

USDA-NRCS Chariton County MO Field Office

University of Missouri Soil & Plant Test Lab

University of Missouri Agroforestry Center

MMI Laboratories, Athens, GAWard Laboratories, Kearney, NE

Dr. Keith Goyne, SEASDr. Randy Miles, SEASDr. Ann Kennedy, USDA-ARS, Pullman, WA

Cover Crops X Soil HealthBiodiversity in a hypothetical block of field soil --Spring oats + berseem clover mixture

Source: Reganold et al. 1990.

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

•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.

Crimson clover provides Carbon and Nitrogen to soils

Example of Structural Diversity:

Soil Microbial Diversity (Soil Biodiversity)[biodiversity = most valuable property of any ecosystem; E.O Wilson, 1999]

Biodiversity • Provides numerous pathways for primary production and ecological

processes (i.e., nutrient cycling) • Many processes require multiple organisms (“Consortia”) for completion• Alternative pathways available if one is disturbed • Ecosystem stability and resistance to stress• Microbial biomass may withstand stress; diversity may be reduced

Fungi

Bacteria

Algae

Nematode

Berg & Smalla, 2009

Soil Microbial Structure and Biological Functions (“Functional Diversity”) Influenced by Plant Roots

Rhizodeposition - 20-60% photosynthate released into rhizosphere (depending on plant)

Extensive root systems of some native prairie plants

Source: Conservation Research Institute

Ideal “functional diversity” in healthy soil provided the diverse microbes necessary for efficient nutrient cycling

Note: Example for only one of the numerous functions microbes mediate in soils

Cover Crops & Maintenance of Soil Organic Matter -“organic matter in the soil may be considered our most important national resource”- Albrecht, 1938.

Living Cover Crops

Actively growing roots deliver C and nutrients to rhizosphere microorganisms

*Greater retention of root C increases C sequestration compared with cash crop residue incorporation (Puget & Drinkwater 2001)

Microbial functions enhanced: nutrient transformations; decomposition; plant growth regulator synthesis; aggregate formation; degrade/inactivate synthetic chemicals

Active rhizobia & mycorrhizae symbiosis; associative N fixation

Cover Crop Residues

Organic matter inputs, building microbial biomass

Provide mineralizable nutrients; active decomposition

Increased microbial diversity; potential pathogen & weed suppression

Improved soil aggregate stability

Increased number, diversity, activity of soil micro-, macro fauna

SOM Components

Crop residueCrop residue

BacteriaBacteria

FungiFungiActinobacteriaActinobacteria

SOMSOM

CO2

Kremer & Kussman, 2011

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

4.50

5.00

2002

20

03

2004

20

05

2006

20

09

2010

20

11

2012

% Soil O

rgan

ic M

aer

Kura Clover

Fescue

Tilled Crop

Kura clover stand in alleys young pecan orchard in September 2006

Soil health indicator: Soil organic C (Soil organic matter)Perennial Cover Cropping with Kura Clover as Alley Crop in Pecan

Chariton County, MO

Soil organic matter consists of at least 3 pools of organic matter

Passive SOM500 – 5000 yrsC/N ratio 7 – 10

Active SOM1 – 2 yrs

C/N ratio 15 – 30

Slow SOM15 – 100 yrs

C/N ratio 10 – 25

• Recently deposited organic material• Rapid decomposition• 10 – 20% of SOM

• Considered most sensitive OM indicator of soil health

• Intermediate age organic material• Slow decomposition• 10 – 20% of SOM

• Very stable organic material• Extremely slow

decomposition• 60 – 80% of SOM

12

13

0

20

40

60

80

100

120

140

160

Grass buffer Agroforestry Row Crop

Act

ive

C (g

/m2)

aa

b

Active Carbon content for three management systems on Mexico sil, Northeast Missouri. Veum, 2011

[little information on active C contents in cover crop management systems]

Treatments with high biomass and continuous root systems contribute to higher AC and biological activity.

SOIL HEALTH: continued capacity of soil to function as a vital living system whereby plant and animal growth and environmental quality is sustained; a holistic approach in which plant, animal, and human health is promoted

Site-specific – comparisons limited within a given landscape;Assessment based on management imposed within a landscape;“Inherent soil quality” is not considered

Missouri (Menfro silt loam)

Brazil (‘Oxisol’)

NOTE: Contrast “inherent soil quality” vs soil quality manipulated via management

Physical Chemical

Biological

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

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

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

• 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 indicators

Microbial Diversity-detected using Phospholipid Fatty Acids (PLFA) analysis

• Structural components of cell membranes in living organisms• Represent microbial community structure and biomass – “population fingerprint”• Indicate nutritional imbalances and environmental stress in soil microorganism

Unger et al. 2012

Functional microbial diversity

Versatility of mycorrhizae fostered by cover crops

Fungal mycelial strands extend plant roots into greater soil volume

Contact remote organic substances – mineralize P, N, S to return to plant and release for subsequent crops

Solubilize P, S, K for plant uptake

Mycorrhizae and Cover Crop Implications

Faculty of Biology Genetics, University of Munich

Lehman et al., 2012Increased AMF propagules specific for numerous crop host plants

Corn and weeds (henbit‐ left) or intercropped w/late summer cover crops (spring oat and berseem clover) –Shown ≈ 70 days after planting – Nov 2012

Cover Crop – weed suppression and soil quality effects

050100150200250300350400450

Oat Henbit Henbit (Oat)

mg root / cm3

Root density (volume)

90 days after cover crop seeding

0

20

40

60

80

100

120

umol

e pr

oduc

t/kg

soil/

hFall 2001Spring 2002Spring 2003Fall 2003Spring 2004Fall 2004Spring 2005Fall 2005

Soil dehydrogenase activityOat cover cropWeed checkLSD (0.05)=18

0

10

20

30

40

50

Wat

er-s

tabl

e ag

greg

ates

(%)

Fall 2001Spring 2002Spring 2003Fall 2003Spring 2004Fall 2004Spring 2005Fall 2005

Soil water-stable aggregatesOat cover cropWeed check

LSD (0.05)=7.0

Oats as a Cover Crop for Managing Winter Annual Weeds

Oat cover crop improved soil quality –increased soil aggregation and soil microbial activity ‐ in addition to suppressing winter annual weeds and potential SCN inoculum potential

Kremer, 2005

Soil Health root bioassays detect potential seedling pathogens associated with particular cover crop management practices – useful in adjusting management strategySchenck et al. 2013 ASA Abstracts.

Soil Health Index for Assessing Crop Management Systems can be Derived based on selected Soil Health Indicators

Example from assessment of various ecosystems within Salt River Basin (Mark Twain Lake watershed)So

il H

ealth

Inde

x

*Livestock grazing

Cover crops –

- Enhance microbial activity and SOM, improving soil health - important to sustained soil and crop productivity and maintaining the environment

- Component of Biological Soil Management that is linked to Soil Health

“Soil health is considered the major linkage between conservation management practices and achievement of major goals of sustainable agriculture”Doran et al. 1999.

STRATEGY:Cover CroppingResidue managementOrganic recyclingIntegrated biological management

SOILHEALTH

GOAL:Sustainable ProductionResource conservationEnvironmental healthPest suppression

Parr et al. 1992. Am. J. Altern. Agr. 7:5-11

Selected References

• Andrews, S.S., D.L. Karlen, and C.A. Cambardella. 2004. The soil management assessment framework: a quantitative evaluation using case studies. Soil Sci. Soc. Am. J. 68:1945-1962.

• Karlen, D.L., G.E. Varvel, J.M.F. Johnson, J.M. Baker, S.L. Osborne, J.M. Novak, P.R. Adler, G.W. Roth, and S.J. Birrell. 2011. Monitoring soil quality to assess the sustainability of harvesting corn stover. Agronomy Journal 103:288.

• Karlen, D.L., S.S. Andrews, B.J. Wienhold, and T.M. Zobeck, Soil quality assessment: past, present, and future. J. Integrat. Biosci. 6:3-14.

• Miles, R.J. and J.R. Brown. 2011. The Sanborn Field Experiment: Implications for long-term soil organic carbon levels. Agron. J. 103:268-278.

• Stiles, C.A., R.D. Hammer, M.G. Johnson, R. Ferguson, J. Galbraith, T. O’Green, J. Arriaga, J. Shaw, A. Falen, P. McDaniel, R.J. Miles. 2011. Validation testing of a portable kit for measuring an active soil carbon fraction. Soil Sci. Soc. Am. J. 75:2330-2340

• Stott, D.E., C.A. Cambardella, R. Wolf, M.D. Tomer, and D.L. Karlen. 2011. A soil quality assessment within the Iowa River South Fork Watershed. Soil Science Society of America Journal 75:2271-2282.

• Stott, D.E., S.S. Andrews, M.A. Liebig, B.J. Wienhold, and D.L. Karlen. 2010. Evaluation of β-glucosidase activity as a soil quality indicator for the Soil Management Assessment Framework (SMAF). Soil Science Society of America Journal 74:107-119.