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elements
K (2.1%)
8
90 elements are
naturally occurring
on planet Earth
> 99%
of the
Earth’s
crust
Elemental concentrations in soil vs. earth’s crust
0.001%
0.01%
0.1%
1%
10%
100%
Plant essential elements are green
Light green elements are exceptionally
enriched in soil relative to crust
soil
crust
Adapted from Essington (2003)
These are not the only elements found in plants!
~ 18 elements have been
identified as essential for
the growth of all plants
Soil
C OH
air & water
N K Ca Mg P S
Cl Fe Mn Zn B Cu Mo
macronutrients
micronutrients
0.1%
V
Co
Ni
Needed by
some plants
Na
Si
Essential element criteria
Organisms cannot complete their life cycles without EE
EE are not replaceable by other elements
and/or
EE are proven to be necessary for specific
physiological functions
Essential elements are all relatively light elements
Some elements (e.g. Se, I, As, Cr)
have been identified as essential for
animals but not for plants.
Boron is the only element that has been
identified as essential for plants
but not for animals
Micronutrients are important components of enzymes
What is an enzyme?
Enzymes are biomolecules that lower
the activation energy required for
biochemical reactions
minerals
Soil solids
Where
are the
contain in
nutrients
nutrients
soil ?
organic
matter
Soil water contains nutrients
H 20
K+
H 20
Ca+2
Mg+2 H20
- --Humus
--
H 20
H20
exchangeable
ions
H 20
Clay
H20
SO4
Al+3
-2
++
H 20
--
+
Ca+2
H 20
H 20
H20
soil
solution H20
H20
- Na
K+
H20
H20
What’s in the soil soup ??
Fe+3
DOM
Ca+2
NO3-
Ca+2
+2
NO3- Mg
+2
H
PO
2
4
Ca
Cu+2
DOM
-
K+
K+ NO3
+2
Ca+2 Mg
Zn+2
DOM
Mg+2
Fe+3
NO3-
DOM
Ca+2
SO4-2
Adapted from Brady and Weil (2002)
crop removal
Amount of nutrient in the soil
Re-seasoning the soup
Modified from Havlin et al. (1999)
Which forms of nutrients are available to
plants ?
“active” OM
humus
exchangeable
weatherable
minerals
solution
Clay mineral
Fe
Fe
- -
Fe
Fe
O
O
-
P
O
O
Inner sphere
HPO4-2 anion
Outer sphere
Ca+2 cation
Diffuse ions
Adapted from Brady and Weil (2002)
Inorganic nutrient forms taken up by plants
Co2+
Plants take up mostly inorganic forms of nutrients
when inorganic forms of nutrients are readily available
In some natural ecosystems (e.g., tundra), organic
forms of nutrients are very important
Nutrient
availability
varies with pH
Micronutrient
deficiencies
frequently
occur when
naturally acid
soils are
over-limed
http://www.fftc.agnet.org/library/image/bc51002p7.html
Avoid over-liming !!
Understanding nutrient uptake
H 20
Root growth
N, S, P
Root exudates
activate soil microbes
NO3-
Transpirational
stream
H 20
Ca+2
+
Diffusion
K+
H2PO4-
Both
strategies
important
!
Feed
the
soil vs.are
Feed
the crop
Healthy roots
available inefficiently…
nutrients !
Unhealthy
rootsneed
use nutrients
Acute
root
disease
Chronic root
malfunction
Small increases in OM can
improve macro-aggregation
Superior air/water relationships
Healthier root
growth and function
Aluminum
toxicity
Aluminum
toxicity
Classic concept of yield
response to nutrient availability
……
Crop yield
Micronutrients
Macronutrients
tend to have a
tend
to have
narrow
a broad
sufficiency
range
sufficiency
range
Deficiency
Symptoms
Nutrient availability
How can we assess the availability of nutrients in soil?
Goals of routine soil testing
Rapid
Cheap
Predictive
Widely
applicable
Very different from research analysis of soil
By themselves, extractable
nutrient levels are not informative.
Extractable nutrient levels provide an index of
nutrient availability that can be interpreted
using results from field experiments.
Illinois Agronomy Handbook
Crop response to soil test P in IL
Critical level for corn and soybeans
Build and maintenance approach
On average, 9 lbs of fertilizer P2O5 are needed
to raise soil test P levels by 1 lb/acre
On average, 4 lbs of fertilizer K2O are needed
to raise soil test K levels by 1 lb/acre
Meaningful interpretation of soil test results
requires field calibration
100 %
yield
50 %
yield
Soil test P concentration (ppm)
http://www.ipm.iastate.edu/ipm/icm/2003/11-17-2003/mehlich3.gif
moisture
temperature
microbial activity
Extractable nutrient levels are not
directly related to most of the factors
controlling nutrient availability during
a growing season.
rooting depth
root health
http://www.extension.umn.edu/distribution/horticulture/components/M1190fig1.htm
Relatively immobile nutrients
Relatively mobile nutrients
So what about
Nitrogen?
Nitrogen is an integral component of
many essential plant compounds
Amino acids
Proteins enzymes
Nucleic acids
Chlorophyl
2.5 - 4% of
plant dry matter
Relationship between optimal N rate
and optimal corn yield in IL (72 site years)
Only 13 out of 72 site-years in IL required more than 1 lb of N per bushel
too high 96%
of the time
1.2 : 1 line
1 : 1 line
too high 82%
of the time
BOTTOM LINE
There is no line that fits this data
well
Yield is a poor predictor of optimal N
rate !!
Well-fertilized crops often obtain more
Where
does
the N
Nfrom
come
from
than half
of their
SOM
?
Why
more
soil
N?
Magdoff
and Weil SOM
(2003)
More productive soils normally supply more
N from
Weather often regulates crop productivity more than
nutrient input rates in high productivity systems
http://www.fertilizer.org/ifa/publicat/PDF/2005_ag_frankfurt_lammel_slides.pdf
The on-going process of N shifting from one form
to another is collectively called the N cycle
Soil
Plant biomass
Why is nitrate such a slippery character ?
• Nitrate is an anion
• Nitrate compounds are very soluble
• Nitrate is next in line as an electron acceptor
when O2 is not present
Denitrification
NO3-
NO2-
NO
N2O
N2
Warm, anaerobic conditions + OM
promote rapid denitrification
GreenSeeker Technology
Some day soon
soil testing
may consist of
on-the-fly “sensing”
of soil hundreds to
thousands of times
per acre like a
yield monitor
water
Justus von Liebig
discovered, through the
analysis of hundreds of
samples of plant ash, that
Law of
plants contain
the elements
Minimumpotassium,
such as sodium,
calcium, and phosphorus.
He concluded that the
minerals contained in
plants must come from the
soil and that without
fertilization, the mineral
content of soils could
become exhausted,
rendering the land
unproductive for agricultural
purposes.
Justus von Liebig (1803 -1873)
Slide from a recent student presentation in
my upper level nutrient management class.
 Soil sampling is the
only manual step left
in the process. With
the implementation of
robotic samplers, the
number of samples will
increase and the cost
per sample will
decline, thereby
enhancing the
economic return and
the advancement of
soil testing knowledge.
 The are at least a
dozen primary factors
which impact crop
yield potential. A study
a number of years ago
ranked soil fertility as
#9!
 Development of new
technologies will
eventually lead to new
knowledge systems for
managing crop
production.