Harnessing the Power of Soil

Biology Dr. Mike Lehman

U.S. Dept. of Agriculture -Agricultural Research Service

Brookings, South Dakota

USDA-NRCSScience 322:49

American Academy of Microbiology (2008)

Microbes Make the Earth Inhabitable

...yet, our knowledge of soil microbial ecology borders on primitive”

In fact, “we are living in a microbial world…

Soil’s where lots of them live

Below surface microbial biomass ≈ all combined above ground biomass!

A BILLION bacterial cells per soil gram

Thousands of “species”

Microbes: The Unseen Majority

Whitman (1998)

Fungi: millionsAlgae: 10,000 - 3 million

Protozoa: up to 1 million

Nematodes: dozens

1 gram of soil

In addition to the 1 billion bacteria in one gram of soil:

Huge Diversity of the “Unseen Majority”

The Three Domains

Grow < 65ºCGrow > 80ºCGrow > 80ºC

ChlorophyllChlorophyllNo chlorophyll

No methanogensNo methanogensMethanogens

Gene System IIGene System IGene System II

80S Ribosome70S Ribosome70S Ribosome

Ester-linked lipids

Ester-linked lipids

Ether-linked lipids

Linear DNA 4 to 308 chromosomes

Circular DNA 1 chromosome

Circular DNA 1 chromosome

EukaryoteProkaryoteProkaryote

EukaryaBacteriaArchaea

Functional Diversity: the Proteobacteria

DeltaproteobacteriaS, NO2

- Oxidizers S Reducers Bacterial Predators

AlphaproteobacteriaHeterotrophsCH4, S, Fe, H2 OxidizersN2 Fixers

GammaproteobacteriaHeterotrophsNO2

-, S, Fe, H2 OxidizersN2 Fixers

BetaproteobacteriaHeterotrophsNH3, Mn, S, Fe, H2 OxidizersN2 Fixers

We live, as we have always lived, in the

“age of bacteria”

Steven Jay Gould (1996)

A Couple of Simple Questions about the Soil:

What kinds of microbes are there?

What are they doing?

Let’s Take a Look

Under the Microscope

In Culture

Less than 0.1% of the microbes present

Might not be active ones

Probably behaving differently

Now recognize the boundless extent of diversity and complexity…..

(1977) M. Alexander

(1994)(2002)

(2006)

(2011)

(2006)

Microbial & Agroecosystems

• Organic matter decomposition

• Nutrient cycling

• Soil structure

• Water management

• Symbiotic relationships

• Pathogen and pest control

2013

So, microbes do a lot of stuff, but what about my

production system?

How are they affected by

my management?

How can I favor the

beneficial types and

activities?

C3

Agricultural Systems

SustainableProduction

Conservation

Tillage

Cover Crops

Crop Rotation

Which handles the elements better?

Free Energy, Carbon, Nitrogen

Better infiltrationMore storageLess water erosionLess wind erosion

Who Likes Black Dirt?Only if you

don’t like food and cover

There’s way more food over

here

More friends

, too

And, more

hiding spots

We’re dying

over here

It’s too hot!

It’s too dry!

And I forgot my shades

& sunscreen

Not much food

And the plow took

out my fungal friends

My neighbors were washed & blown

away!

No comme

nt

Using Cover Crops to Improve the Internal

Cycling of N

inorganic soil N immobilized on-site in plant biomass

prevents loss: leaching, denitrification, volatilization

Augmented by N-fixation (leguminous cc)

Biomass N gradually mineralized to ammonium reduces losses

Ammonium oxidized to nitrate (nitrification)

Nitrogen Fixation/Mineralization

Convert Atmospheric Nitrogen to Plant Available

Timed release to following Crop

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

Clover Fallow Rye Vetch

Cover Crop Nitrogen Mineralizationmg N/cm3

T3

T2

T1

ECTOS

Arbuscular Mycorrhizal

Fungi

• More volume• Small pores• Increased uptake

(1000x surface area)

• Enzymes• Chelators• pH

AMF Make Plants

Drought-Resistant

More AMF = More Straws

Diverse AMF = More Access

Fungal Hyphae

Root

Fungal spores, hyphae, and glomalin

Photo credit: Sara Wright

AMF reduce erosion

Soil Aggregation

Soil Structure

Water Infiltration & Storage

AMF Increase Water Storage

Plus AMF No AMF

Sorghum at 22 days

Root Biomass

Shoot Biomass

Plant Diversity

HyphalLength

Soil POlson

Plant

TissueP

Van der Heijden, et al. 1998

Number of arbuscular mycorrhizal fungal species

Low #s can stress plant

Affected by: Tillage ↓ fallow; flooding ↓ rotation, host

plants ↓↑ P concentration ↓

AMF & Ag Management

Agricultural Soil

Prairie Soil0

200

400

600

800

1000

1200

1400

AMF Spores in SoilS

pore

s per

50m

l S

oil

AM

F D

ivers

ity

Cropped Field

Prairie

Boosting Native Mycorrhizae with Cover

Crops

0

5

10

15

20

25

30

35

40

45

50

AM

F P

rop

agu

les/

100

g S

oil

Cover Crops and Soil AMF Propagules: Brookings Research Farm

2009

2010

0

20

40

60

80

100

120

140

160

Cover Crops None

AM

F P

ropagule

s/100 g

soil

P < 0.01

Arbuscular Mycorrhizal Fungi (AMF), Ideal, SD, Nov 2010

cover crops: cow pea-winter pea-millet-turnip-radish

Capturing AMF Diversity with Cover Crops

1

11

10

00

0

002

3

3

4 5

Wheat

Oat Clover

Vetch

Building Soil BiotaSoil organisms need:

Food• Diverse crop rotation = diverse foods

• Continuous cover (perennials, cover crops, long-season crops) = consistent source

Habitat• Stable aggregates that are not destroyed by tillage

• Diversity of plants = diversity niches

Benefits from Soil Microbes

Soil Structure & Aggregation

Pathogen & Pest Protection

Soil Carbon N fixation

Plant Growth Promoters

Weed Suppression

Nutrient Availability

Nutrient Retention

NutrientsPest

ProtectionYield Yield

Pass-Thru Self-Sustaining

Lost Lost$ $

Progress by Multidisciplinary Research: Acknowledgement and Promotion

Dr. Shannon Osborne

Dr. Wendy Taheri Dr. David Douds

Research funding: U.S. Dept of Agriculture, Agricultural Research ServiceSouth Dakota Corn Utilization Council