Z. Kabir, Ph.D.Soil Health Specialist for CA, NV & PIA

USDA-NRCS, Davis, CA

Arbuscular Mycorrhizal Fungi (AMF)in Soil Health Paradigm

Outline

• AMF and soil health functions• Impact of tillage practices on AMF• Effects of land fallow on AMF• Alternative to no-till practices on AMF• Combined effects of tillage & fallow on AMF• Cover crops in relation to AMF• Conclusions

Plant and Mycorrhizal Symbiotic Relationship

Carbohydrate

P & other nutrients

AMF

P Transport by AM Hyphae

Root Soil

PO4P depletion zone

2 mm 1 mm

Stele

AM hyphae

P uptake by AMF (adapted from Hayman, 1982)

Arbuscule& vesicle

100 mm

T-DNA Carrot Root and AMF

Photo:Kabir

Hypha

spore

Soil

Impact of AMF on Soil Stability

Kabir

Fall Tillage Spring Tillage

Tillage Practices

Seasonal Changes of AM Hyphae in Tillage Systems

Kabir et al.

Spring Disk Fall Plow

Apr Jun Aug Oct Apr

Seasonal and Vertical Distribution of AM Hyphae in NT and CT

0

100

200

300

400

500

600

700

1

2

3

4

05

1015

2025

Hyp

hal d

ensi

ty (c

m c

m-3

)

Growing

perio

d

Depth (cm)

NT

0

100

200

300

400

500

600

1

2

3

4

05

1015

2025

Hyp

hal d

ensi

ty (c

m c

m-3

)

Growing

perio

d

Depth (cm)

CT

Kabir, 2005

Influence of Tillage on AM Species

Scutellospora spp.

Boddington and Dodd found disappearance

Kabir et al. observed disappearance

G. aggregatum Glomus spp.

Sieverding observed 75%

G. scintillans

in plowed soil while 5% in NT

in CT

Tillage and Soil Aggregate Stability

Treatments Soil depth 0-5 cm 5-10 cm Grass 53.2a 42.2b NT 3 yr 37.7c 24.4de NT 2 yr 30.8cd 26.4de NT 1 yr 25.0de 24.8de CT 4yr 16.7f 20.8ef

Comparison of aggregate stability across treatments of no-till (NT) and conventional tillage (CT) corn at two soil depths.

Wright et al.

Intact AMF in No-till System

Williams et al. 2016

Soil Functional Zone Management

Spatial Distribution of AM Hyphae

Mid-row

Quarter-row

Row

Sandyloam soilA

ctiv

e hy

phal

leng

th (c

m c

m-3

)

50

100

150

200

250

300

Tota

l hyp

hal l

engt

h (c

m c

m-3

)

100

150

200

250

300

350

400CT RT NT

Clay soil

Row Quarter-row Mid-row Quarter-rowRow Mid-row1992 1993

Row Quarter-row Mid-row1992

Spatial Distribution of AM Hyphae in two Soils

Kabir et. al.Ag.Ecosys. & Environment

Fallow Soil Erosion

Land Fallowing

Harinikumar and Bagyaraj

40% reduction after one season of fallow

13% reduction when a non-AMF plant in rotation

In Australia, Thompson showed that mycorrhizal colonization, P, Zn uptake, yields of various crops are inversely related to the duration of the fallow. He called it a long-fallow disorder if fallow period is one year

Effect of Crop Rotation and Fallow on AMF

0 30 60 90Fallow Period (day)

Combined Effects of Tillage and Fallow

Kabir et al.Soil Biol. Biochem.

Cover Crops

AM fungi bridges Cover Crops to the Subsequent Crops

Cover crops die

AM hyphae

Cover crop plot

Fallow plot

Shoo

t P u

ptak

e (m

g)

0

1

2

3

4

5

6

20

40

60

80

100FallowOatsRyeRye & oats

Days after planting

Shoo

t dry

wei

ght (

g)

0.0

0.3

0.6

0.9

1.2

5.0

10.0

15.0

20.0

25.0

c

bb

a

c

b

a a

c

bab

a

c

b

a a

27 42

P uptake and dry weight in Cover Crops and Fallow Fields

Mycorrhizal and Non-mycorrhizal Cover Crops

BuckwheatOats Winter wheat

AM FungiNon-AM Fungi

Sweet Corn Root Colonized by Mycorrhizal Fungi

Days after planting10 20 30 40 50 60 70

Myc

orrh

izal

col

oniz

atio

n (%

)

0

20

40

60

80

100

Fallow Buckwheat Oats Winter wheat

*

*

*

*

*

*

Shoo

t P u

ptak

e (m

g)

0

5

10

15

20

25

FallowBuckwheatOatsWinter wheat

c cb

a

cc

b

a

Days after planting 14 31

Corn

sho

ot d

ry w

eigh

t (g)

0

1

2

3

4

c c ba

cc

b

a

Corn P uptake and Shoot Dry Weight

Suitable Crop Rotation

Corn following Soybean (Mycotrophic)

Corn following Canola(Non-mycotrophic)

Koide, BYU

Hyphal Length and Soil Aggregates in Cover Crops and Fallow Field

AM hyphal length (m g-1)

0 10 20 30 40 50 60

Wat

er s

tabl

e so

il ag

greg

ates

(%)

10

20

30

40

50

60

FallowRyeOatsRye + Oats

R2 = 0.39Hyphal length = 19.06 + 0.74 (%WSA)

P < 0.05

Kabir and KoidePlant and Soil

• Judicial manipulation of agronomic practices would benefit AMF survival and its benefits

• Minimal or no disturbance of soil improve AM fungal propagules and its diversity

• Mycotrophic plant in cropping systems throughout year would improve AM fungal survival and benefit to the soil and crops

Conclusions

Thank You

Ear Production of Corn in Different Cover Crops Treatments

Annual Plants P uptake

Plants take up-10-20 % applied P

AM fungi

AM Hyphae Produced Phosphatase

Koide & Kabir

Seasonal and vertical distribution of Spore in NT and CT

0

10

20

30

40

50

0

1

2

34

5

05

1015

2025Sp

ore

dens

ity (n

o. c

m-3

)

Growing

perio

d in N

T

Depth (cm)

Spor

e de

nsity

(no.

cm

-3)

0

10

20

30

40

50

0

1

2

34

5

05

1015

2025

Growin

g pe

riod

in C

T

Depth (cm)