1)  Briefly summarize your professional experience related to soilscience/soil management (you may want to share a resume/CV).

2) How have you acquired your current knowledge of soil science ? Pleasediscuss any of the following that have made a significant contribution(academic coursework, internships, on-the-job experience, books, journals, conferences, mentoring)

3) Describe a memorable experience in the field that taught you somethingabout soil.

4) How have soil science principles/technologies changed during yourcareer?

5) What activities/opportunities would you recommend for undergraduatestudents to discover if a career similar to yours is appropriate for them?

6) From your experience, what tillage practices do you find to be the mostbeneficial for corn and soybean production?

Interview projects – Due May 5 (transcript and ~ 1 page reaction)

Biologically active

SOM

SOM is a complex mixture

Living organisms

Recent residues

Recalcitrant SOM

Adapted from Magdoff and Weil (2003)

HUMUS

“The microherd”

Phil Brookes

Generally makes up 1-5% of SOM

Plow layer ~ 2 million lbs/acre

3% of 2 million = 60,000 lbs

3% of 60,000 = 1,800 lbs

General rule of thumb for corn

grain, stover and roots each comprise ~1/3rd of the OM produced by corn

How much OM is returned to the soil by a 200 bushel corn crop?

200 bushels*56 lbs/bushel = 11,200 lbs * 2 = 22,400 lbs of OM

2/3rds of corn OM

What is humus ???

Humus is organic matter that has been transformed such that its original source is no longer apparent… The diverse products of “humification” have many common characteristics:

Extreme chemical complexity Resistance to further decomposition High specific surface and negative charge Dark color

2400

http://www.grida.no/climate/vital/graphics/large/12.jpg

Global C cycle

Gt = 109 t = 1 billion metric tons

Soil > Atmosphere > Vegetation

< 1 year

decades

centuriesWhat is the mean residence time of SOM ??

SOM pools

Janzen (2006)

The oldest SOM is most

abundant!

Pool = an accumulation of something

Why is SOM important ??

mostly digests organic matter

Soil macro-aggregates form around organic residues

Tillage disrupts aggregates and accelerates decomposition

Tillage OM inputs Tillage OM inputs

Humus adsorbs ions and molecules

Adapted from Brady and Weil (2002)

Humus increases plant available H20

Adapted from Brady and Weil (2002)

SOM reduces bulk density

Magdoff and Weil (2004)

Additional OM has

little effect

(Watts and Dexter, 1997)

Structuraldamage Soils with high OM

are more resistant to structural damage !

Humus gives soil a darker color

Is this beneficial?

Understanding organic resource quality

(Giller, 2000)

aka digestibility

Relationship between fine mineral fraction and SOM

Magdoff and Weil (2004)

Weak relationship between clay content and SOC for 1261 agricultural soils in England and Wales

Webb et al.(2003)

Many recent studies have shown that physical fractions of OM are related to soil function

HumusSand sized Silt and clay sized

http://www.grdc.com.au/growers/res_summ/pdfs/cso00029.pdf

Particulate OM

Location within the soil matrix affects SOM dynamics

Adapted from Carter (2002)

Mineral associated OM

Intra-aggregate

POM

Free POM

Sensitivity to management

↑

↑

Temperature affects SOM dynamics

Brady and Weil (2002)Temperature

Organic matter destruction by aerobic organisms

Organic matter synthesis by plants

Org

anic

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ter

accu

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Above ~ 70 F,decomposition tends to exceed photosynthesis

70 FOrg

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atte

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on

OM

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Illinois in 50 yrs

Interstream divide

SOIL DRAINAGE CLASSES

Poorly drained

Somewhat poorly drained

Moderately well drained

Poorly drained

Well drained

Interfluve

Valley floorBackslope

Shoulder

LANDSCAPE POSITIONS

Landscape position affects SOM dynamics

Where does the most OM accumulate?

Blackland soils of North Carolina

Lily (1981)> 1 million acres of Histosols

Geographic distribution of SOM

How much

is enough ?

?

Janzen (2006)

Hydroelectric dam metaphor

There are many ways to “measure” SOM

Adapted from Strek and Weber (1985)

Total organic matterby mass loss by ignition

Total C by several wet and dry oxidation methods

Humic matterby alkali extraction

C ~ OM/1.72

% OM

25 yrs CT corn

20 yrs sod, 5 yrs CT

corn

Soil from a long term

experiment in Beltsville, MD

After adding water

1.4 % C1.0% C

Relatively small differences in SOC

48 bu/a 140 bu/a

Large differences in soil function

Perennial forages are an excellent way to improve soil structure and OM content !

DEPARTMENT of DEPARTMENT of SOIL SCIENCESOIL SCIENCENC STATENC STATE UNIVERSITY UNIVERSITY

(justification statement)

Small increases in OM can improve macro-aggregation

Superior air/water relationships

Healthier root growth and function

20 years of similar tillage intensity and total organic inputs but contrasting types of organic inputs

Crop residuesCover Crops

Animal manure

Crop residues

Aggregation changes more rapidly than total C

Jastrow (1996)

16 % clay 39 % 49%

More OM is needed to stabilize fine textured soils

Adapted from Russell (1973)

16 % clay39 % 49%

Permanganate oxidizable C

a routine test for “active” soil C ??

Managing SOM

Adapted from Bailey and Lazarovits (2003)

A systems approach Well adapted crop

NutrientManagement

WaterManagement

SOM

http://www.extension.umn.edu/distribution/cropsystems/components/7402_02.html

Agriculture normally accelerates loss of SOM

Why does agriculture have this effect?

well mixed vs.stratified

Conventional tillage Conservation tillage

Adapted from House and Parmelee (1985)

Effect of tillage on microbial activity

Havlin et al. (1999)

Tillage

The primary factors controlling microbial activity vary with time

Which tillage system has more microbial activity ?

Microbial activity w/ tillage

Microbial activity without tillage

+ SOM

More OM accumulates at the surface in no-till systems but accumulation in the whole soil profile may be similar in production systems with tillage

Artificial drainage has greatly increased the number of days when soils in the Upper Midwest are suitable for

field operations

but has also contributed

to many environmental

problems

Pollution of water resources Loss of SOM

On-farm sources of OM

Crop residues

Innovative cover cropping

Erosion Control Practices

Crop Rotation

High residue crops

Cover crops

Forages

Off-farm sources of OM

pHSoluble salts

Herbicide residuesTrash

?

Large scale composting

Saturation deficit

Saturation of capacity

Actual C

Attainable C

Potential C

(Dick and Gregorich, 2004)

Disturbance factors

Input factors

capacity factors

3 main types of factors regulate

soil C stocks

man

agem

ent

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