SOM management: have your cake and eat
it too
Michelle M. [email protected]
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 fertility1850s
• 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
Theoretical functions describing the influence of soil quality on yield response and input use efficiency:
Ya= initial or optimal stateYb= 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-1; M: Amended with manure, lime and phosphorus since 1904,
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.
Inputs
None
Man
ure
Man
ure+
NPK
MNPK
HNPK
Cor
n Y
ield
(K
g/ha
)
1255
2510
3766
5021
6276
7531
8786
10042
11297
Continuous CornCorn-SoybeanCorn-Oat-Hay
Inputs
1 2 3 4 5 6 7
Yie
ld
20
40
60
80
100
120
140
160
180
200Y
Yb
Ya
YcYd
a) b)
U MMPS
UNPKMNPK
HNPK
Mea
n H
arve
sted
Mas
s 19
67-2
000
(kg
ha-1
)
2000
3000
4000
5000
6000
7000
8000
9000
10000
U MMPS
UNPKMNPK
HNPK
Mea
n C
orn
Yie
ld 1
967-
2000
(kg
ha-1
)
2000
4000
6000
8000
10000
12000
a b
Continuous CornCorn SoybeanCorn Oats Hay
Continuous CornCorn SoybeanCorn Oat Hay
N Balance (Inputs- N harvested)
U M MPSUNPK
MNPKHNPK
-50
0
50
100
150
200
CCCSCol 73
N (
kg h
a-1)
c
Mean Harvested MassYield response to inputs
Inputs
*
U MMPS
UNPKMNPK
HNPK
pH
5.0
5.5
6.0
6.5
7.0
U MMPS
UNPKMNPK
HNPK
P (
lbs
ac-1
)
0
25
50
75
100
U MMPS
UNPKMNPK
HNPK
K (
lbs
ac-1
)
200
225
250
275
300
325
350
375
400
CCCOCOH
U MMPS
UNPKMNPK
HNPK
SO
C (
g C
kg-
1 so
il)
15
20
25
30
35
U MMPS
UNPKMNPK
HNPKN
test
s (m
g N
kg-
1 so
il)
150
200
250
300
350
U MMPS
UNPKMNPK
HNPK
PO
M (
g C
kg-
1 so
il)
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
CCCSCOH
What would Liebig think?
Nutrient cycling through organic reservoirs
During transition one accumulates nutrient stocks held in and supplied from an organic matter reservoir
Fundamental shift of decomposer community to the left
Low N availability High N availability
Adapted from Schimel and Bennett, 2004
Organic N
NH4+
Plants and microbes actively
compete
NH4+
Limited competition, net mineralization becomes
active
NO3-
Pro
po
rtio
n o
f N
tak
en u
p
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
Biologically Active SOM
Physically Active SOM
Chemically Reactive And Humified SOM
Nutrient Supply
Disease Suppression
Erosion Resistance
Water Holding Capacity
INPUTS
Cation Exchange
Pesticide Sorption, Efficacy
NH4+Plants and microbes actively compete and partner
NO3
NH4
Limited competition,
Net mineralization
important
Organic N
A. Simple agronomic systems that rely on inorganic N/ P and are frequently C limited
C. Natural and diversified systems that are C rich and N/P limited
B. Diversified systems that are C and N/P rich
Grand unified field theory
King et al., 1934
“..the manure increases the number and activities of competitive org-anisms which inhibit the growth and development of the root rot fungus.”
Biologically active matterassociated with nutrient supply or microbial growth
Physically active or sequestered matter associated with substrate accessibility and soil structure
Chemically active or inactive matterexplains or influences material persistence and it’s chemical reactivity including exchange and sorption-de sorption properties.
All SOM is not created equal
• 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
Active Fractions
Particulate (Macro) Organic Matter
Sensitive to management
Indicator of root inputs
Stabilizes macro aggregates
Positively related to soil N supply
Substrate supporting biological growth
MNR LEG CNV
mg
C (L
F) g
soi
l-1
1.00
1.25
1.50
1.75
2.00
2.25
MNR LEG CNV
mg
N (L
F) g
soi
l-1
0.06
0.07
0.08
0.09
0.10
MNR LEG CNV
mm
ol C
O2
g L
F C
day
-1
0.00
0.05
0.10
0.15
0.20
Wander et al. 1996
Rotation, POM
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
systemsEmily 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
Stepwise multiple regression
Dependent variable†
Model adjusted R2 value
Partial R2 values‡
MAT MAP % clay % silt age
All systems
SOC 0.788*** 0.211 n.s. 0.514 0.086 n.a.
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.
Organic systems
SOC 0.851*** 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. 0.639
Diagnostic for soil condition
Low N availability High N availability
PO
M Q
uan
tity
an
d Q
ual
ity
High Proportion of SOC
Lower C/N ratio
Mgt:Organic matter: the meat and the bone
Rapid decomposition Sugars
Cellulose
Proteins
Hemicellulose
Lignin
HumusSlow dec
omposition
Cover crops
Compost
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 animalsIllustration from National Geographic
• 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 non-offensive odor
• Weed seeds, pathogens killed
• No time restrictions
Raw Manure Composted Manure
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
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