1) briefly summarize your professional experience related to soil science/soil management (you may...
TRANSCRIPT
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
mat
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accu
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Above ~ 70 F,decomposition tends to exceed photosynthesis
70 FOrg
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atte
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rga
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um
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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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