The science and management

The Furrow

soil biology

of

Joel Gruver

WIU Agriculture

j-gruver@wiu.edu

Is conventionally

managed soil a

biological ghost

town?

Even soils receiving intensive tillage

and chemical inputs contain billions of

bacteria per gram of soil

Phil Brookes

Microherd

The soil beneath our feet may be teeming with a hundred

times more species of bacteria than previously thought,

according to biologists in New Mexico, US.

Measuring the bacterial biodiversity of soil is difficult

because only a few species can be cultured, according to

Jason Gans of the Los Alamos National Lab.

Fortunately, biologists can also estimate biodiversity

using a technique called DNA reassociation. This involves

chemically unzipping the two strands of all the bacterial

DNA in a sample, mixing them up and seeing how long

they take to join up again with matching partners.

SSSA

Their results reveal that there are a few

very common species in soil but lots of rare

species. "There is a very large number of

low abundance species," says Gans. So

many rare species, in fact, that the estimate

of bacterial biodiversity rises to ~ 1 million

species per gram of soil.

How much of the C in these corn stalks

will return to the atmosphere within 1

year?

> 75%

This is not possible without an active

microbial community

Corn

yie

ld

1950

30 b/a

150 b/a

A

B

C

Which trajectory for

SOM is most common

in the US?

How is it possible for

residue levels to

increase > 3x without

building SOM?

Broadbalk continuous wheat experimentData modelled by RothC-26.3 (solid lines)

0

20

40

60

80

100

1820 1840 1860 1880 1900 1920 1940 1960 1980 2000 2020

Year

Organic C in soil

(t C ha-1) Farmyard manure annually

Unmanured

NPK

Why has the NPK program

resulted in so little increase in

SOM?

So

il C

(to

ns/h

a)

unfertilized

The manure and NPK systems are both producing > 100 bu/a wheat

The current OM level in a soil is a

result of the long-term balance

between organic inputs and outputs

The current OM level in a soil is a

result of the long-term balance

between organic inputs and outputs

Yield enhancing practices will not build

SOM if OM outputs increase at a

comparable rate to OM inputs

Organic outputs

”But with the removal of water through furrows, ditches, and

tiles, and the aeration of the soil by cultivation, what the

pioneers did in effect was to fan the former simmering fires…

into a blaze of bacterial oxidation and more complete

combustion. The combustion of the accumulated organic

matter began to take place at a rate far greater than its annual

accumulation. Along with the increased rate of destruction of

the supply accumulated from the past, the removal of crops

lessened the chance for annual additions. The age-old process

was reversed and the supply of organic matter in the soil began

to decrease instead of accumulating.”

William Albrecht – 1938 Yearbook of Agriculture

Drainage + Tillage + Lime + N + harvest = Accelerated loss of SOM

20 years of similar tillage and total organic

input but different types of organic inputs

manure

cover crops

crop residues crop residues

How do these soils differ ??

Rodale Institute Farming Systems Trial

http://www.grdc.com.au/growers/gc/gc48/conference1.htm

The development of

crumb structure is

a key step in

retaining SOM

Granular crumb structure Poor structure

We are well aware that a poorly

balanced diet for humans results in

heart disease, tooth decay,

obesity… what are the

consequences of feeding soil a

“white bread” diet?

White bread diet for soil = very little diversity of organic inputs

Acute

root

disease

Chronic root

malfunction

VS.

Unfortunately this is the

norm in agriculture

today :-<

Dramatic effect of steam

sterilization and compost on

growth of pepper plants

http://picturethis.pnl.gov/im2/8208417-5cn0/8208417-5cn.jpg

The digestive

capacity of soil

microorganisms

greatly exceeds

organic inputs to

soils.

accumulate at all

in soil?

So

why does

mat org anic ter

In the long run

…it remains largely unknown why some SOM persists for

millennia whereas other SOM decomposes readily…

Recent analytical and experimental advances have

demonstrated that molecular structure alone does not

control SOM stability: in fact, environmental and biological

controls predominate…

Nature, October 2011

The traditional concept of

large stable humus

molecules has been

rejected by most scientists

Mined humate products may

have value but are not the

same as old soil organic matter

Blackland soils of

North Carolina

Lily (1981)

> 1 million acres

Organic matter accumulates under anaerobic conditions

Impact of temperature on SOM accumulation

Brady and Weil (2002)

Temperature

Org

an

ic m

att

er

dyn

am

ics

Organic matter accumulates

in climates that support high

biomass production but limit

decomposition

Impact of temperature on plant growth

Brady and Weil (2002)

Temperature

Org

an

ic m

att

er

pro

du

cti

on

Impact of temperature on decomposition

Brady and Weil (2002)

Temperature

Org

an

ic m

att

er

co

ns

um

pti

on

Visualizing soil

habitat at biologically

relevant scales

Worm’s eye view?

Nematode’s eye view?

Visualizing soil habitat at

relevant scales

Bacteria occupy

< 5 % of soil surfaces

and < 0.1% of soil

porosity

Most of the pores where soil

microorganisms reside are either

environmentally suppressive or

lacking in suitable substrates.

Microorganisms have very limited ability to

move within the soil matrix.

As a result,

soil is a very sleepy place !

osmobiosis

anoxybiosis

thermobiosis

cryobiosis

anhydrobiosis

Most soil microorganisms are

in a dormant state

waiting…

For their prince charmings

to arrive !

Roots

Organic Amendments

Rain

There are many types of prince charmings !

Tillage

Dormant earthworm

SSSAJ 69(3) cover

Earthworm cocoons

offer much more protection

http://soils.usda.gov/sqi/soil_quality/soil_biology/images/CE8a-cocoon_LR_small.jpg

Most plants in your

soils are in a state

of dormancy

Seed dormancy

is much better

understood

than

microbial

dormancy

Who lives in the soil?

Bacteria

Fungi

Algae

Protozoa

Nematodes

Microarthropods

Enchytraeids

Earthworms

Ants, termites, spiders

Mollusks

Others: rodents, snakes,

voles, amphibians, etc.

Body size

increasing

Microflora

Mesofauna

Megafauna

Microfauna

Macrofauna

Soil organisms vary widely in size

Bacteria

Fungi

Algae

Protozoa

Nematodes

Microarthropods

Enchytraeids

Earthworms

Ants, termites, spiders

Mollusks

Others: rodents, snakes,

voles, amphibians, etc.

Microflora aka microbes

Mesofauna

Megafauna

Microfauna

Macrofauna

Most soil organisms are tiny !!!

Abundance

Soil

microbes

carry out

> 90% of all

decomposition

Soil animals have a

disproportionate impact on

nutrient cycling, energy fluxes

and plant growth

Soil animals are mobile

but have limited digestive ability

Soil microbes are relatively immobile

but have almost unlimited

digestive ability fungi bacteria

3 main types of digestive interactions

occur between soil animals and microbes

I want some

bacteria for

lunch ! Microfauna (e.g. protozoa and nematodes)

harness the microbes’s digestive abilities by

grazing on them

Microbivory

NH4+

NH4+

NH4+

NH4+

NH4+

NH4+

External

rumen

digestion

When mesofauna feed on fresh litter, their fecal

pellets contain shredded, moistened and mixed

but largely undigested residues

Reingestion of fecal pellets after a few days of

microbial activity greatly increases assimilation

Many

microarthropods use this digestive

strategy

Leaf cutter ants are a more

well known example of

external rumen digestion

Internal rumen digestion

greatly enhances utilization

of complex substrates by

soil macrofauna

Macrofauna are also

ecosystem engineers

Do roots and

macrofauna play

similar ecological

roles?

bacteria

root hair

rhizoplane

Microbial activation

Structural modification

Structural modification

Microbial activation

Navigating the rhizosphere

Rhizoplane

Endo-

Rhizosphere Ecto-Rhizosphere Root free soil

End of the rhizosphere

(Lavelle and Spain, 2001)

> 100 X

microbial

activity

Growing

Root

Aggregate

Disruption

Exudation

Release of protected

organic matter

Activation of

microorganisms

Priming

Effect

Why do roots have a priming effect?

(Lavelle and Spain, 2001)

Soil

organisms

are

concentrated

in

HOT

SPOTS !

Adapted from Coleman et al. (19??)

drilosphere porosphere

detritusphere aggregatusphere rhizosphere

middens casts

Drilosphere

Zone of

earthworm

influence

Detritusphere

surface residue zone

fungi

Clean tillage

eliminates the

detritusphere

Many soil organisms prefer to

feed at the surface

3 main

strategies for

managing soil

biology

Activation

Augmentation Conservation

Not all earthworms are sensitive to tillage…

but the ones that make vertical burrows

that connect the topsoil and subsoil are…

Earthworm functional

continuum

Epigeic Anecic Endogeic worms worms worms

Ectomycorrhizae

Arbutoid

mycorrhizae

Ericoid

endomycorrhizae

Orchid endomycorrhizae

AM endomycorrhizae

Mycorrhizal diversity

Lavelle and Spain (2001)

Most woody plants

Most herbaceous

plants including

corn and soybeans

Myco = fungus

Rhiza = root

•Many plants are

connected

underground by

mycorrhizal hyphal

interconnections.

•Mycorrhizal fungi

are not very host

specific.

Illustration by Mark Brundrett

Mycorrhizal Networks: Connecting

plants intra- and interspecifically

Mycorrhizal inoculants are available

but conservation of established networks is more important

Increase nutrient uptake

(especially P)

suppress pathogens

Mediate plant competition Improve soil structure

Glomalin

Superglue

of the soil ??

Mycorrhizae

Are you conserving the beneficial

fungi on your crop foliage?

Frogeye leafspot fungus resistance to strobilurin

chemistry a concern for Mid-South soybean growers Hembree Brandon - Mar. 2, 2011 5:36am

Add another to the growing list of weeds, insects, and diseases that have

developed resistance to the chemicals that farmers rely on to control pests and

protect yields — strobilurin-resistant Cercospora sojina, the fungus that causes

frogeye leafspot in soybeans.

The strobilurin chemistry has been widely used as a first line of defense in

preventing yield loss from Frogeye leafspot.

―There was documentation in 2010 of strobilurin-resistant Cercospora in Illinois,

Kentucky, and Tennessee,‖ Tom Allen said at the annual conference of the

Mississippi Agricultural Consultants Association.

Roots

Organic Amendments

Rain

Tillage

Biological activation strategies

Irrigation

Innovative cover cropping

is a great way to activate

your soil biology!!

Bio-strip till

attempt #1

September 2008

Radish planted on 30” rows using milo plates

in mid-August 2010

Attempt #3

Cover crop system Relative

corn yield

Volunteer oats 79%

Radishes planted on 30‖ 99%

Radishes drilled on 7.5‖ 91%

Corn following cover crop experiment in

2011 at the WIU Organic Research Farm

Corn planted on radish rows

Wheat + radish trial at the Allison farm

November 2010

3 lb/a = 2 lb/a = 1 lb/a > 0 lb/c

~ 2.5 bu/a yield boost

Is this an activation effect?

Have you tried any

biological seed

treatments?

Augmenting soil biology

Old school inoculation

http://www.beckerunderwood.com/en/pages/scienceofinoculation

VOTiVO contains a naturally occurring soil bacteria, or rhizobacteria, that live

and grow with the plant’s root system. The bacteria creating a biofilm that

becomes a living barrier limiting the number of receptor sites which could

otherwise be occupied by plant pathogens such as nematodes. Nematodes

use gaseous and solid exudates from the root as means to detect a root’s

proximity, so reduced levels of exudates can decrease the ability of the

nematodes to locate the receptor sites on the roots. The bacteria further

reduce viable nematode populations by consuming exudates, depriving

nematodes of an additional source of energy and nutrients.

competition parasitism

antibiosis induced resistance

Ask vendors to explain specifically

how their product works!

If you build it, they will come…

Do recognize this scene?

The most important biological management strategy