SOM management: have your cake and eat

it too

Michelle M. Wandermwander@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 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

MIT

Mineralization, Immobilization, Transformation

NH4+

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

N2O & NO3-

NO3- & NH4

-C-NH3 , N2, & NH+4

-C-NH3 & NH+4

Changing the nature of nutrient cycles

Organic and occluded P

Organic and occluded

Inorganic and labile P

Inorganic and labile 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

Brown vs Green ManureBrown 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

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

CF-C CF-N IL-N .

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

Consider

• Amendments

• Rotation

• Nutrient budgeting

• Visual assessment or tissue testing

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

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