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Using Soil Fertility Practices to Solve Problems on Your Farm
Laurie Drinkwater
Cornell University
NOFA-VT, January 19, 2010
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Soil ecology: Plant-microbe interactions
Break-out session
Management strategies and tools for problem solving
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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)
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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
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Biological processes & dynamic soil traits
Organic matter
additionsIncrease soil
life & diversity
Decomposition
Nutrients
release
Plant growth
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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
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F = fungal hyphae
RH = root hair
M = mucigel
Dense bacterial colonization
Rhizosphere =Plant-soil interface
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Rhizosphere
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Plant
Soil
Microbes
The rhizosphere
o
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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.
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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∆
∆
∆
∆
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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
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Plant microbial interactionsand soil fertility
1. Plants influence soil microbial community composition in a very short time frame.
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Decomposition
ORGANIC RESIDUE
HUMUS
NUTRIENT RELEASE
(NH4+, PO4
=, SO4=)
HEAT
CO2
PRIMARY
DECOMPOSERSbacteria
fungi
mineralization
assimilation
humification
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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.
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Nitrogen cycling is TEN times greater in the rhizosphere compared to bulk soil.
(Firestone, 2004)
Roots and mineralization of SOM
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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
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Swarm of protozoa grazing on red fluorescent bacteria
Bringhurst et al. (2001) PNAS
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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
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Soil from conventional and organic plots after 18 years of management
ORGCNV
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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
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Roots secrete carbon: ExudatesSugars, amino acids, enzymes
Rhizosphere microbes also secrete sticky compounds and promote aggregate formation adjacent to roots increasing drought tolerance.
o
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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.
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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
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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.
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• 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
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• 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
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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
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SOIL ORGANIC MATTER CONTINUUM
Easily decomposed
Resistant to decomposition
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ORGANIC MATTER CONTINUUM
Easily decomposed
green manure
compost
Resistant to decomposition
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Soil Organic Matter Fractions
Living
Recently dead
Dead but protected
Very dead
(Passive)
ORGANIC
RESIDUES
Active
SOM
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Optimizing biological N fixation
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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
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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
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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
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Soil N pool
Fixed N
N fixation decreases as soil N fertility increases
Compost N additions
o
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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
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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
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N fix
Soil nitrogen
Fixed N
How do non-legumes impact N fixation?
Competition for soil nutrients.
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How do non-legumes impact N fixation?
N fix
Soil nitrogen
Fixed N
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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
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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
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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
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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
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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
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Compost pile sampling protocol
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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
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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