Using Soil Fertility Practices to Solve Problems on Your Farm

Laurie Drinkwater

Cornell University

NOFA-VT, January 19, 2010

Soil ecology: Plant-microbe interactions

Break-out session

Management strategies and tools for problem solving

Soil fertility has consequencesat multiple levels

Animal & human health

Soil management: Nutrient availability, SOM dynamics, microbial community (pathogens, competitors, symbionts, decomposers), the soil physical environment

Crop health, yield,food quality

Plant community (weeds)

Arthropod community (herbivores, predators,

parasitoids)

Challenges to organic nutrient management

Nutrient release: Complex living and environmental processes

We can only estimate the capacity of soils to provide nutrients

Don’t know the amount of nutrients being added (soil amendments, N-fixation)

Uncertain about the proportion of nutrients that will be released from these residues

o

Biological processes & dynamic soil traits

Organic matter

additionsIncrease soil

life & diversity

Decomposition

Nutrients

release

Plant growth

Biological processes & dynamic soil traits

Organic matter

additionsIncrease soil

life & diversity

Decomposition

Nutrient

release

AggregationPore structure

improved

Humus

formation

Disease

suppression

Improved tilth

Plant growth

F = fungal hyphae

RH = root hair

M = mucigel

Dense bacterial colonization

Rhizosphere =Plant-soil interface

Rhizosphere

Plant

Soil

Microbes

The rhizosphere

o

How do plants influence soil microbial community composition?

Soil from a 50-year corn field

+

Legume and grasses commonly used as cover crops; crops grown in rotation with corn.

Greenhouse-grown replacement plants in corn-soil.

Corn (∆) and no plant (ƒ) treatments were used to determine the

baseline microbial community.

ƒ

ƒ

ƒ

ƒ∆

∆

∆

∆

Soil microbial diversity after six weeks

0

20

40

60

80

100

120

140

160

180

200

corn

Soy

bea

n (m

o.)

vetch

Italian Rye

gras

s

buck

whea

t

alfalfa

Soy

bea

n (d

o)

Whe

at

Tritica

le

no plant

Mic

rob

ial d

iversit

y in

dex

Series3

Series2Series1

Unique species

Present in Corn and other plants

Common in all samples (common soil microbe)Maul and Drinkwater, 2010

Plant microbial interactionsand soil fertility

1. Plants influence soil microbial community composition in a very short time frame.

Decomposition

ORGANIC RESIDUE

HUMUS

NUTRIENT RELEASE

(NH4+, PO4

=, SO4=)

HEAT

CO2

PRIMARY

DECOMPOSERSbacteria

fungi

mineralization

assimilation

humification

0

2

4

6

8

10

12

100%

219%

308%

so

il-d

eri

ved

CO

2(g

C p

ot-

1)

Plants and SOM

decomposition

Wheat doubled and

soybean tripled

SOM decomposition

rates.

Cheng, W., SSSA 2002.

Nitrogen cycling is TEN times greater in the rhizosphere compared to bulk soil.

(Firestone, 2004)

Roots and mineralization of SOM

Bacteria, fungi

C

N

P

C,N,PGrazer

Ni, Pi

C,N,PPredator

Ni, Pi

Clarholm, 1985; Ingham et al., 1985; Ferris, 1998, Chen and Ferris, 1999.

Food web in the rhizosphere: Plays a key role in delivering plant nutrients

o

NP

Swarm of protozoa grazing on red fluorescent bacteria

Bringhurst et al. (2001) PNAS

Plant microbial interactionsand soil fertility

1. Plants influence soil microbial community composition in a very short time frame.

2. Plants stimulate microbes to breakdown organic matter and release nutrients like nitrogen.

3. Grazers in the rhizosphere play a key role in releasing these nutrients to the plant.

o

Soil from conventional and organic plots after 18 years of management

ORGCNV

Modified after P. Puget-1997

Incorporation

of plant residues

& roots (POM)

Colonization &

microbial growth

Aggregate formation:

trapping of POM

Biodegradation:

decline of microbial activity

Loss of

aggregate

stability

Aggregate Formation and Stabilization

Roots secrete carbon: ExudatesSugars, amino acids, enzymes

Rhizosphere microbes also secrete sticky compounds and promote aggregate formation adjacent to roots increasing drought tolerance.

o

Rhizosphere and aggregation:lupin and wheat.

Crop Aggregate stability

(MWD, mm)

Microbial biomass C

(ug g-1)

Fungal hyphae (m g-1)

Active

bacteria

(no. x 109)

Lupin 0.49 320 1224 8.1

Wheat 0.30 300 310 5.8

Haynes and Beare, Soil Biol. Biochem. 29:1647-1653, 1997.

0

10

20

30

40

50

60

%

Occluded POM

0

25

50

75

100

%

Free POM

Shoot-derived C

Root-derived C

Fate of vetch C

Loss of C in particulate organic matter fraction occurs within one growing season

AT T0 about 50% of root-derived C is present as O-POM & C loss from this pool proceeds at a

slower rate

Puget and Drinkwater 2001

May 121997

Oct 71997

May 18

1998

Oct 28

1998

Plant microbial interactionsand soil fertility

1. Plants influence soil microbial community composition in a very short time frame.

2. Plants stimulate microbes to breakdown organic matter and release nutrients like nitrogen.

3. Grazers in the rhizosphere play a key role in releasing these nutrients to the plant.

4. Cover crops, and legumes in particular, promote aggregate formation and improve soil tilth.

• Soil ecology: New understanding of plant-microbe interactions

• Break-out session

– Is there a fertility-related problem or challenge you are currently facing?

– Do you have an example of a soil fertility management practice/strategy that is working well on your farm?

• Management strategies and tools for problem solving

o

• Soil ecology: New understanding of plant-microbe interactions

• Break-out session

– Is there a fertility-related problem or challenge you are currently facing?

– Do you have an example of a soil fertility management practice/strategy that is working well on your farm?

• Management strategies and tools for problem solving

o

Soil organic

matter

Biological community:

plant growth, size and

composition of soil

community

Soil structural

properties:

aggregation,

water holding

capacity, water

infiltration

Hydrology

Nutrient

cycling:

N, P, S

SOIL ORGANIC MATTER CONTINUUM

Easily decomposed

Resistant to decomposition

ORGANIC MATTER CONTINUUM

Easily decomposed

green manure

compost

Resistant to decomposition

Soil Organic Matter Fractions

Living

Recently dead

Dead but protected

Very dead

(Passive)

ORGANIC

RESIDUES

Active

SOM

Optimizing biological N fixation

Why legumes in organic systems?

Legume cover crops are the primary source of new N

Build SOM and improve soil health

Contribute to active cycling of N and P in soil

Promote aggregate formation

Legumes can access P that is stored in soil and transfer it into active SOM for subsequent cash crops

Nitrogen fixation is regulated by a complex set of factors

Environmental

Biological

–Plant, microbe species

–Symbiosis

–Community (+ and –)

–Plant-microbe-soil interactions

http://www.csuchico.edu/bccer/Ecosystem

Environmental factors that impact N fixation

Climate and soil fertility

Nitrogen availability impacts N fixation rates

Phosphorus is also important. P limitation can reduce growth of N fixing plants

Micronutrients are also important--Molybdenum (Mo) and cobalt (Co) are involved in biological N2-fixation

pH--N fixation is inhibited in acid soils

Soil aeration: N fixation is energy intensive, high oxygen demand

Soil N pool

Fixed N

N fixation decreases as soil N fertility increases

Compost N additions

o

The response of N fixation to soil fertility varies, depending on availability of P and N

Increasing soil fertility

Nitro

ge

n fix

atio

n

P, other nutrients

are limiting N availability increases,

N fixation is inhibited

P, other nutrients

no longer limiting

0

40

80

120

rye

alone,

N from

soil

vetch

alone,

N from

air

vetch

in mix,

N from

air

rye

alone,

N from

soil

vetch

alone,

N from

air

vetch

in mix,

N from

air

rye

alone,

N from

soil

vetch

alone,

N from

air

vetch

in mix,

N from

air

rye

alone,

N from

soil

vetch

alone,

N from

air

vetch

in mix,

N from

air

high available soil nitrogen low soil available nitrogen

lb N

/ac f

rom

so

il (

for

rye)

or

air

(fo

r vetc

h)

v. low

vetch

Biomass, NDFA

estimated

2 high N fields

2 low N fields

Fields with greater soil fertility had reduced N fixation

N fix

Soil nitrogen

Fixed N

How do non-legumes impact N fixation?

Competition for soil nutrients.

How do non-legumes impact N fixation?

N fix

Soil nitrogen

Fixed N

Proportion of N coming from nitrogen fixation in monocultures

versus mixes for Field Pea and Vetch on Northeast Organic Farm

fields

0%

20%

40%

60%

80%

100%

alo

ne

mix

alo

ne

mix

alo

ne

mix

alo

ne

mix

alo

ne

mix

alo

ne

mix

alo

ne

mix

alo

ne

mix

alo

ne

mix

alo

ne

mix

alo

ne

mix

alo

ne

mix

alo

ne

mix

1 2 3 4 5 6 7 8 9 10 11 12 13

13 rye/vetch fields

N fixation rates on NE organic farms are greater in mixes

Cowpea fixed more N when intercropped w/Japanese millet

Cover crop species% N from fixation

Total N fixed

(lbs/ac)

Cowpea 39 37

Cowpea + Japanese millet 72 59

Cowpea + SorgumSudan 56 26

Forage soybean could not compete with either grass species

Cover crop species% N from fixation

Total N fixed (lbs/ac)

Forage soybean 67 88

Forage soybean + Japanese millet 82 28

Forage soybean + SorgumSudan 90 35

Optimizing use of legumes

•Need to balance compost additions to avoid suppressing N fixation

•Legumes are a great complement to compost

•Mixes showed less variation across farms– good strategy

•Challenging to balance weed suppression and N fixation

Keep track additions and removals

Relationship between Biomass Index (% cover x height) and total N

uptake for Red Clover biomass

R2 = 0.62

0

50

100

150

200

250

0 500 1000 1500 2000 2500 3000

Biomass index (% cover x height cm)

N in aboveground

biomass (kg/ha)

Tools for quick estimates of green manure nitrogen inputs

Compost pile sampling protocol

Biological processes & dynamic soil traits

Organic matter

additionsIncrease soil

life & diversity

Decomposition

Nutrient

release

AggregationPore structure

improved

Humus

formation

Disease

suppression

Improved tilth

Plant growth

Thank-you

Acknowledgements

Lab group: Ann Piombino, Jennifer Gardner, Meagan Schipanski, Steven Vanek, Christina Tonitto, Julie Grossman, Burtie van Zyl, Megan Gregory, many, many field and lab assistants. We thank the many farmers who contributed to this research.

Funding: USDA-

Organic Program,

NRI/Managed

Ecosystems, NE

SARE