SOM management:
have your cake and eat
it too
Michelle M. Wander
mwander@uiuc.edu
Natural Resouces and Environmetnal
Sciences UIUC
Organic Fertility
Soil and soil management is the
foundation of organic production.
Organic growing systems are soil
based, care for the soil and
surrounding ecosystems and
provide support for a diversity of
species while encouraging nutrient
cycling and mitigating soil and
nutrient losses.
IFOAM Norms, 2002
Modern notions of soil fertility
1850s
• Justis von Liebig disproves the ‘humus
theory’ and formulates the law of the
minimum
• Louis Pasteur proves decay is a biotic
process
“Humus benefits the
soil in three ways:
mechanically,
as a plant food,
and by fundamentally
modifying the soil
bionomics. Of the three,
this last, hitherto
largely ignored, is
probably the most
important".
Lady Eve Balfour- In "The Living Soil" 1943
Corn Yield Trends in Morrow Plots are Influenced by Soil Quality
200
YYa
180
11297
10042
8786
Corn Yield (Kg/ha)
140
Yc
Yd
120
100
80
7531
6276
5021
Continuous Corn
Corn-Soybean
Corn-Oat-Hay
3766
60
40
2510
a)
20
b)
H
N
PK
ur
N
PK
M
N
PK
M
Inputs
an
7
e
6
M
5
ur
4
an
3
N
2
e+
1255
1
on
e
Yield
160
Yb
Inputs
-1
Theoretical functions describing the influence of soil
quality on yield response and input use efficiency:
Ya= initial or optimal state
Yb= reduced input use efficiency
Yc= reduced yield potential
Yd= reduced input use efficiency and yield potential
From Cassman, K.G. PNAS. 1999, 96: 5952-5959.
 U: Unamended since 1876 seeded with 8000 plants ac ;
Amended with manure, lime and phosphorus since 1904,
 M:
 seeded 8000 plants ac-1 ;
 MPS: Amended with manure, lime and phosphorus since 1904 ,
 seeded 12000 plants ac-1 ;
UNPK:
U plots amended with NPK (200, 45, 336 lbs ac-1) since 1967,

 seeded with 24000 plants ac-1 ;
 MNPK: Former M plots are amended with NPK since 1967,
 seeded with 24000 plants ac-1;
HNPK: Former M plots amended with high NPK rates (300, 112, 560 lbs ac-1)
since 1967, seeded with 24000 plants ac-1.
Mean Harvested Mass
Yield response to inputs
10000
12000
c
b
*
8000
6000
4000
Continuous Corn
Corn Soybean
Corn Oats Hay
9000
8000
Col 73
7000
6000
5000
U
M
K
K
K
PS
M UNP NP HNP
M
100
50
4000
Continuous Corn
Corn Soybean
Corn Oat Hay
3000
2000
2000
CC
CS
150
N (kg ha-1)
10000
Mean Harvested Mass 1967-2000 (kg ha-1)
a
Mean Corn Yield 1967-2000 (kg ha-1)
200
N Balance
(Inputs- N harvested)
0
-50
U
Inputs
M PS PK PK PK
M UN
N HN
M
U
M
S K K K
MP UNP MNP HNP
What would Liebig think?
7.0
400
100
50
0
275
200
U M PS PK PK PK
M UN N HN
M
U M PS PK PK PK
M UN N HN
M
U M PS PK PK PK
M UN N HN
M
5.0
CC
CS
COH
25
20
POM (g C kg-1 soil)
35
SOC (g C kg-1 soil)
300
225
5.0
30
325
250
25
N tests (mg N kg-1 soil)
5.5
CC
CO
COH
350
75
K (lbs ac-1)
6.0
-1
P (lbs ac )
pH
6.5
375
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
15
U M PS PK PK PK
M UN N HN
M
U M PS PK PK PK
M UN N HN
M
35
0
30
0
25
0
20
0
15
0
U M PS PK PK PK
M UN N HN
M
Nutrient cycling through organic
reservoirs
During transition one accumulates nutrient stocks held in and
supplied from an organic matter reservoir
MIT
NH4+
Mineralization, Immobilization, Transformation
Proportion of N taken up
Fundamental shift of decomposer
community to the left
NH4+
Plants and
Organic N
microbes actively
compete
NH4+
Limited competition, net
mineralization becomes
active
Low N availability
Adapted from Schimel and Bennett, 2004
NO3-
High N availability
Changing the nature of nutrient cycles
NO3- & NH4
-C-NH3 , N2, & NH+4
N2O & NO3-
-C-NH3 & NH+4
Inorganic and labile P
Organic and occluded P
Inorganic and labile P
Organic and occluded
Modify Plant-Microbe Relations
• Reliance on N fixation
as a source of N
• Mycorrhyzal
associations
• Plant induced
liberation of nutrients
• General suppression
of soil borne disease
Enhance the physical ecology
• This supports the biotic community
• Promotes the efficient cycling of
matter and energy while
• helping soils and resident organisms
to resist stress
Nutrient Supply
Biologically Active SOM
Disease Suppression
INPUTS
Physically Active SOM
Erosion Resistance
Water Holding Capacity
Chemically Reactive
And Humified SOM Cation Exchange
Pesticide Sorption, Efficacy
Grand unified
field theory
NO3
A. Simple agronomic
systems that rely on
inorganic N/ P and are
frequently C limited
NH4
Organic N
C. Natural and
diversified systems
that are C rich and
N/P limited
B. Diversified
systems that are
C and N/P rich
NH4+
Plants and microbes actively compete and partner
Limited
competition,
Net
mineralization
important
King et al., 1934
“..the manure increases the number and activities of competitive organisms which inhibit the growth and development of the root rot fungus.”
All SOM is not created equal
Biologically active matter
associated with nutrient supply or microbial growth
Physically active or sequestered matter
associated with substrate accessibility and soil
structure
Chemically active or inactive matter
explains or influences material persistence and it’s
chemical reactivity including exchange and sorptionde sorption properties.
Active Fractions
• Biologically active
– Plant available-N, N mineralization, Amino
sugar N
– Microbial respiration, biomass size, ratios
– Particulate organic matter
– Microbial activity, substrate decay potential
• Physically active
– Particulate organic matter
– Aggregation
– Residue
– Carbohydrates, Amino sugar N
Particulate (Macro) Organic Matter
Sensitive to management
Indicator of root inputs
Stabilizes macro aggregates
Positively related to soil N supply
Substrate supporting biological growth
Rotation, POM
2.25
-1
0.10
1.75
1.50
mmol CO2 g LF C day
mg N (LF) g soil-1
mg C (LF) g soil-1
2.00
0.09
0.08
0.07
1.25
1.00
Wander et al. 1996
0.15
0.10
0.05
0.00
0.06
MNR LEG CNV
0.20
MNR LEG CNV
MNR LEG CNV
Brown vs Green Manure
Quantity and quality of labile SOM
in organic and conventional soils
• 9 long-term farming systems trials NA
– 10 years old on average
– All include organic and conventional
systems
Emily Marriott’s M.S. thesis
Types of Farming Systems
• Conventional
– Fertility from synthetic fertilizers
– 8 sites
• Manure-based organic
– Fertility from compost or manure
– 7 sites
• Legume-based organic
– Fertility from N2 fixing legumes
– 3 sites
40
% Increase Above Conventional
Manure-Based Organic
Legume-Based Organic
a
a
a
a
30
20
a
a
a
a
a
a
10
0
TOC
TN
POM C
CF-C
SOM Fraction
POM
Sugar. N
CF-NN Amino
IL-N
Stepwise multiple regression
Dependent
variable†
Model
adjusted
R2 value
Partial R2 values‡
MAT
MAP
% clay
% silt
age
SOC
0.788***
All systems
0.211 n.s.
0.514
IL-N
0.789***
0.239
n.s.
0.450
0.123
n.a.
POM-C
0.398***
n.s.
0.420
n.s.
n.s.
n.a.
SOC
0.851***
Organic systems
0.222 n.s.
0.608
0.049 n.s.
IL-N
0.857***
0.231
n.s.
0.570
0.083 n.s.
POM-C
0.615***
n.s.
n.s.
n.s.
n.s.
0.086
n.a.
0.639
POM Quantity and Quality
Diagnostic for soil condition
High Proportion
of SOC
Low N availability
Lower C/N ratio
High N availability
Consider
•
•
•
•
Amendments
Rotation
Nutrient budgeting
Visual assessment or tissue testing
Mgt:Organic matter: the meat and the bone
Sugars
Cover crops
Cellulose
Proteins
Hemicellulose
Lignin
Compost
Humus
Oshins, 1999
Soil
Stewardship
• Tighten the nutrient cycle,
• Increase nutrient and water
use efficiency,
• Suppress diseases and
pests, including weeds,
• Resist degradation,
• Buffer environmental
onslaughts,
• Produce healthy plants,
people and animals
Illustration from National Geographic
Raw Manure
Composted Manure
• High available
nutrients: N forms,
P, K, etc.
• Heterogeneous,
high volume
• Very biologically
active
• Wet with strong odor
• Contains weed
seeds, pathogens
• 60-90 day time
restriction
• Low available
nutrients, esp. N
• Relatively
Homogeneous,
reduced volume
• Biologically stable
• Moist-dry with nonoffensive odor
• Weed seeds,
pathogens killed
• No time restrictions
Testing and budgeting
• Sample at a consistent time point
• Consistent depth
• Baseline samples
Take home message
• Soils should source organic
• The do this when inorganic amendments
are not easily available
• It is much easier to build biologically active
than physically active SOM
• Accumulation of physically active C
provides evidence that you have reduced
the type A tendencies of your soil