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

4

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

28

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

38

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?

QUESTIONS?Reinbottt@Missouri.edu

573-884-7945