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SOIL HEALTHTim Reinbott and Kerry Clark
Soil health has three main components
• Sustained biological productivity
• Environmental quality
• Plant and animal health
3
IMPORTANCE OF SOIL ORGANIC MATTER (SOM)
Kristen Veum and Robert Kremer
What is Soil Organic Matter?
SOM is derived from Plant residue (both
litter and roots) Animal remains and
excreta Living soil microbes
(microbial biomass) Over time fresh
organic material is transformed into soil organic matter
Crop ResiduesCrop Residues
BacteriaBacteria
FungiFungiActinobacteriaActinobacteria
SOMSOM
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What Destroys Organic Matter? Tilling! Whether It Is a Plow or a
Field Cultivator Loss of Organic
Matter Soil structure Soil microbial
biomass Release of CO2
Soil Erosion
Why Till? Weed Control
Loss of Organic Matter and Loss of Soil Structure
Cover Crops in 2014-Oats and Legumes
Historic Losses of Soil CarbonSimulated total soil carbon changes (0 - 20 cm depth) from 1907 to 1990 for the central U.S. corn belt and a
portion of the Great Plains (Lal et al., 1998).
30003500400045005000550060006500700075008000
Year
So
il C
(g
m-2
)
ConventionalTillage
ReducedTillage
53% of 1907
61% of 1907
8
Agriculture and SOM
20 – 40% of SOM is lost on cultivation Management effects on SOM
Tillage (disturbance) Chemical Fertilization Manure Residue Retention Crop Crop Rotation Cover Crop
9
Decline in SOC from Sanborn Field Plots showing increase following the return of residues beginning in 1950
SOM & RootsSOM is NOT just from crop residues!
10
Soil Organic Matter
58% Carbon P, S, and other
nutrients 95% of Soil Nitrogen in SOM
Cover Crops in Winter-Something Green and Growing Year Around And Feeds The Soil
Biology
Soil Life (macro)Help create soil structure and break down larger plant residues
• Earthworms• Nematodes• Beetles• Ants• Termites• Springtails
One tablespoon of soil has approximately 1 billion soil microbes:
• Bacteria: 3,000,000 to 500,000,000• Actinobacteria: 1,000,000 to 20,000,000• Fungi: 5,000 to 1,000,000• Yeast: 1,000 to 1,000,000• Protozoa: 1,000 to 500,000• Algae: 1,000 to 500,000• Nematodes: 10 to 5,000
Soil Life (micro)
This is the mass equivalent of two cows per acre that need to be fed Soil organisms
are much like cows, they need inputs of plant residues for food and energy
Specifically, they need the carbon that is contained in plant residue and soil organic matter
Feed The Bacteria, Fungi, and other LIfe
The Decay Zone: Top 0-6 inches in the Soil
• Natural ‘tillage’ by earthworms • Burrows enhance water infiltration and soil
aeration. This reduces runoff, and increases soil water storage for dry spells.
• Worms redistribute organic matter and nutrients throughout the topsoil layer.
• The soluble nutrient content of worm casts is considerably higher than that of the original soil.
Earthworms
• General saprophytic fungi (i.e., decomposers)
• Produce glomalin – glue in aggregation• Nutrient cycling! Especially hard to
decompose SOM
Fungi
Fungi Hold The Soil Together
Slake Test
Fungi Hyphae
Mycorrhiza
Bacteria bridge short distances, but fungi can work over long distances to explore and to transport nutrients thanks to their fine hyphal system.
Thus, mycorrhizas (symbioses between roots and fungi) have been very successful in evolution.
Photo: David Read
• Some cause disease• Can keep bacterial and fungal pathogens in check-
keep balance in microbe world• Bacterial feeders may dominate in tilled plots, and
herbivorous nematodes may dominate in no-till (Lenz & Eisenbeis, 2000)• Bacterial feeders may be stimulated by tillage (Wardle,
1995)
• Tillage may promote a bacterial-dominated decomposition pathway (vs. fungal), which in turn supports bacterial feeders.
Nematodes
• Have cells like bacteria and filaments like fungi –(were misclassified as fungi)
• Decompose cellulose and chitin & important in organic matter and nutrient cycling
• Tend to be drought/temp resistant• Responsible for the “earthy” smell of soil due to
geosmin• May produce special chemicals when stressed (e.g.,
under low P, N, or O2) or secondary metabolites (e.g., antibiotics), & some are pathogenic
Actinobacteria(Actinomycetes = old term)
Photo: Wikipedia
SOM Improves Soil Physical Properties
Increased aggregate stability
Increased water infiltration
Reduced runoffIncreased water holding capacity
Decreased erosionImproves aeration and macroporosity
Avoid this!Avoid this!
Photo: iastate.edu
Tilled VS No-Till-We Have Destroyed Much of Our Soil Structure
LONG TERM PASTURE TILLED IN A CORN/SOYBEAN/WHEAT ROTATION
Soybean Switchgrass NT Corn Hedgerow/fescue
Fescue field0
500
1000
1500
2000
2500
3000
PLFA Analysis at Bradford Research Center
Bacteria
Actinomycetes
Fungi
Protozoa
Cropping Type
Bio
mass (
mg
/g)
No Protozoa in Corn/Soybean Rotations.Micro Organism biomass highest in perennial cover
Bradford Research Center, 2012
Soybean Switchgrass NT Corn Hedgerow/fescue
Fescue field0
50
100
150
200
250
300
350
400
450
500
PLFA Sub-categories at Bradford
Rhizobia
Arbuscular Myc-orrhizal
Saprophytes
Cropping System
Bio
mass (
mg
/g)
Soybean-Conventional-had no Mycorrihizae or Rhizobia
All organic matter in soil is not equalScientists describe 3 pools of soil organic matter **really is a continuum of decomposition
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
• Intermediate age organic material
• Slow decomposition• 10 – 20% of SOM
• Very stable organic material
• Extremely slow decomposition
• 60 – 80% of SOM
CO 2
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Results are read in a spectrometer in lab or field or from a color card
Potassium Permanganate TestKMnO4 oxidizes active carbon. The purple color of the chemical changes to pink the more active carbon there is in a soil sample.
Active Carbon in Soil Organic Matter-The Lighter the Color the
MORE Active Carbon
Active Carbon-More In Permanent Polycultures-Cover Crops More
Than No-Till
Is There A Difference in Soil Microbes With Vegetables Under Plastic or Straw?
Table 3. PLFA concentrations
Treatment Total Gram+ Gram− Actino Fungi AM Fungi Protozoa
Bare 15.07 DE 4.45 CD 3.94 DE 2.17 BC 0.42 BC 0.58 DE 0.07 B
Black Poly 13.27 E 4.10 D 3.28 E 1.87 C 0.36 C 0.48 E 0.04 B
White Poly 15.49 CDE 4.61 BCD 4.04 DE 2.20 BC 0.45 BC 0.59 CDE 0.08 AB
Rye 19.33 AB 5.48 AB 5.58 AB 2.69 A 0.61 AB 0.85 A 0.18 AB
Rye Roots 18.39 ABC 5.26 ABC 5.16 ABC 2.53 AB 0.60 AB 0.73 ABC 0.14 AB
Rye Shoots 16.72 BCD 4.90 BCD 4.51 CD 2.41 AB 0.44 BC 0.66 BCD 0.11 AB
Vetch 20.38 A 5.82 A 5.76 A 2.71 A 0.73 A 0.81 AB 0.20 AB
Vetch Roots 19.04 AB 5.47 AB 5.36 ABC 2.59 AB 0.54 BC 0.72 ABCD 0.27 A
Vetch Shoots 17.39 BCD 5.05 BC 4.77 BCD 2.46 AB 0.55 ABC 0.71 ABCD 0.13 AB
Total Soil Microbe Biomass Is Greatest Under Cover Crops, Especially
Mycorrhizae (AM Fungi) Plastic Has Much Less Than Cover Crops!!
Buyer, et al, 2010
Cover Crop Under Plastic Did Not Decompose-Less Microbial Life?
Soil Temperature-10 Degrees Higher Without Cover
Doug Peterson
When soil temp reaches. . .140° F
130° F
100° F
70° F
Soil bacteria die
100% moisture lost through evaporation & transpiration
15% moisture is used for growth 85% moisture lost through evaporation & transpiration
100% moisture is used for growth
J.J. McEntre, USDA SCS, Kerrville, TX, 1956
WATER RELATIONS
Surface crust impedes infiltration.
Open, granular surface structure enhances infiltration.
Biopores (earthworm channel) enhance infiltration.
Conventionally tilled fieldConventionally tilled field
No-till fieldNo-till field
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Aggregate Stability-Better Water InfiltrationFungal-produced glomalin helps bind aggregates
http://ed.fnal.gov/trc_new/pandp/soil_research/soil_aggregates.html
Wright, et al., 1999
From Steve Groff
Cover Crop No Cover Crop
Cover Crops Reduce Water Runoff or Increase Water
InfiltrationNo-Till With Cover Crop Took Several Hours ForWater To Run-Off
Conventionally Tilled-Within 30 Minutes of Rainfall (1.5”/hr)
Water and Soil Started Running Off
Cover Crop Residue Allows Water to Soak Into the Soil
Water Collected From Tilled (left), No-Till (middle) and No-Till With Cover Crop (right)
Flash Drought 2013
Why Was Corn With Cover Crop Bigger?