Download Using Soil Fertility Practices to Solve Problems on Your Farm Laurie Drinkwater

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 consequences
at multiple levels
Animal &
human health
Crop health, yield,
food quality
Arthropod community
(herbivores, predators,
parasitoids)
Plant community
(weeds)
Soil management: Nutrient availability, SOM
dynamics, microbial community (pathogens,
competitors, symbionts, decomposers), the soil
physical environment
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
additions
Increase soil
life & diversity
Decomposition
Nutrients
release
Plant growth
Biological processes & dynamic soil traits
Organic matter
additions
Increase soil
life & diversity
Disease
suppression
Pore structure
improved
Decomposition
Aggregation
Humus
formation
Improved tilth
Plant growth
Nutrient
release
Rhizosphere =
Plant-soil
interface
F = fungal hyphae
RH = root hair
M = mucigel
Dense bacterial
colonization
Rhizosphere
The rhizosphere
Plant
Microbes
Soil
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.
ƒ
∆
∆
ƒ
∆
ƒ
∆
ƒ
Greenhouse-grown replacement plants in corn-soil.
Corn (∆) and no plant (ƒ) treatments were used to determine the
baseline microbial community.
Soil microbial diversity after six weeks
200
Microbial diversity index
180
160
140
120
100
80
60
40
20
Maul and Drinkwater, 2010
So
pl
an
t
no
Tr
iti
c
al
e
t
he
a
W
yb
ea
n
(d
o)
lfa
al
fa
w
he
at
bu
ck
s
gr
as
Ry
e
It
al
ia
n
ve
tc
h
So
yb
ea
n
co
(m
o.
rn
)
0
Series3
Unique species
Present in Corn and other plants
Series2
Common in all samples (common soil microbe)
Series1
Plant microbial interactions
and soil fertility
1. Plants influence soil microbial community
composition in a very short time frame.
Decomposition
ORGANIC RESIDUE
HEAT
CO2
PRIMARY
DECOMPOSERS
bacteria
fungi
mineralization
assimilation
humification
HUMUS
NUTRIENT RELEASE
(NH4+, PO4=, SO4=)
Plants and SOM
decomposition
soybean tripled
SOM decomposition
rates.
soil-derived CO2 (g C pot-1 )
Wheat doubled and
12
10
6
219%
4
2
0
Cheng, W., SSSA 2002.
308%
8
100%
Roots and mineralization of SOM
Nitrogen cycling is TEN times
greater in the rhizosphere
compared to bulk soil.
(Firestone, 2004)
Food web in the rhizosphere: Plays a
key role in delivering plant nutrients
N
P
Ni, Pi
C
Ni, Pi
Bacteria, fungi
N
o
P
C,N,P
Grazer
C,N,P
Predator
Clarholm, 1985; Ingham et al., 1985; Ferris, 1998, Chen and Ferris, 1999.
Swarm of protozoa grazing on red fluorescent bacteria
Bringhurst et al. (2001) PNAS
Plant microbial interactions
and 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
CNV
ORG
Aggregate Formation and Stabilization
Incorporation
of plant residues
& roots (POM)
Colonization &
microbial growth
Aggregate formation:
trapping of POM
Loss of
aggregate
stability
Biodegradation:
decline of microbial activity
Modified after P. Puget-1997
Roots secrete carbon: Exudates
Sugars, amino acids, enzymes
o
Rhizosphere microbes also secrete sticky compounds and
promote aggregate formation adjacent to roots increasing
drought tolerance.
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
Wheat
0.49
0.30
320
300
1224
310
8.1
5.8
Haynes and Beare, Soil Biol. Biochem. 29:1647-1653, 1997.
100
Fate of vetch C
Free POM
75
%
Root-derived C
Shoot-derived C
50
25
Loss of C in particulate organic
matter fraction occurs within one
growing season
0
60
AT T0 about 50% of root-derived C
is present as O-POM & C loss
from this pool proceeds at a
slower rate
Occluded POM
50
40
%
30
20
10
0
Puget and Drinkwater 2001
May 12
1997
Oct 7
1997
May 18 Oct 28
1998 1998
Plant microbial interactions
and 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 plantmicrobe 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 plantmicrobe 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
Biological community:
plant growth, size and
composition of soil
community
Nutrient
cycling:
N, P, S
Soil organic
matter
Hydrology
Soil structural
properties:
aggregation,
water holding
capacity, water
infiltration
SOIL ORGANIC MATTER CONTINUUM
Easily decomposed
Resistant to decomposition
ORGANIC MATTER CONTINUUM
Easily decomposed
green manure
compost
Resistant to decomposition
Soil Organic Matter Fractions
ORGANIC
RESIDUES
Living
Active
SOM
Recently dead
Dead but protected
Very dead
(Passive)
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
N fixation decreases as soil N fertility
increases
Fixed N
Soil N pool
Compost N additions
o
Nitrogen fixation
The response of N fixation to soil fertility varies,
depending on availability of P and N
P, other nutrients
no longer limiting
P, other nutrients
are limiting
N availability increases,
N fixation is inhibited
Increasing soil fertility
lb N/ac from soil (for rye) or air (for vetch)
Fields with greater soil fertility had
reduced N fixation
120
2 low N fields
2 high N fields
80
40
v. low
vetch
Biomass, NDFA
estimated
0
rye
vetch vetch
alone, alone, in mix,
N from N from N from
soil
air
air
rye
vetch vetch
alone, alone, in mix,
N from N from N from
soil
air
air
high available soil nitrogen
rye
vetch vetch
alone, alone, in mix,
N from N from N from
soil
air
air
rye
vetch vetch
alone, alone, in mix,
N from N from N from
soil
air
air
low soil available nitrogen
How do non-legumes impact N fixation?
Fixed N
N fix
Soil nitrogen
Competition for soil nutrients.
How do non-legumes impact N fixation?
Fixed N
N fix
Soil nitrogen
N fixation rates on NE organic farms
are
greater
in
mixes
Proportion of N coming from nitrogen fixation in monocultures
versus mixes for Field Pea and Vetch on Northeast Organic Farm
fields
100%
80%
60%
40%
20%
1
2
3
4
5
6
7
8
13 rye/vetch fields
9
10
11
12
mix
alone
mix
alone
mix
alone
mix
alone
mix
alone
mix
alone
mix
alone
mix
alone
mix
alone
mix
alone
mix
alone
mix
alone
alone
mix
0%
13
Cowpea fixed more N when intercropped
w/Japanese millet
% N from
fixation
Total N
fixed
(lbs/ac)
Cowpea
39
37
Cowpea + Japanese
millet
72
59
Cowpea +
SorgumSudan
56
26
Cover crop species
Forage soybean could not compete
with either grass species
% N from
fixation
Total N fixed
(lbs/ac)
Forage soybean
67
88
Forage soybean + Japanese
millet
82
28
Forage soybean +
SorgumSudan
90
35
Cover crop species
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
Tools for quick estimates of green
manure nitrogen inputs
Relationship between Biomass Index (% cover x height) and total N
uptake for Red Clover biomass
250
200
R2 = 0.62
150
N in aboveground
biomass (kg/ha)
100
50
0
0
500
1000
1500
2000
Biomass index (% cover x height cm)
2500
3000
Compost pile sampling protocol
Biological processes & dynamic soil traits
Organic matter
additions
Increase soil
life & diversity
Disease
suppression
Pore structure
improved
Decomposition
Aggregation
Humus
formation
Improved tilth
Plant growth
Nutrient
release
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: USDAOrganic Program,
NRI/Managed
Ecosystems, NE
SARE