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Of approximately 40 trials that we have conducted over the past three years, in no instance was more than 1.2 lbs of N per bushel
of grain needed to optimize productivity, and in most cases, considerably less was required. Averaged over locations and years, our economic optimum N rates averaged slightly less than 1.0 lbs
per bushel (with a range of almost none to 1.2 lbs). Somewhat surprising were the relatively high yields produced without any supplemental N (generally >>100 bushels per acre), and the fact that the highest optimum N rates were typically associated with
the lowest-yielding environments. http://agronomyday.cropsci.illinois.edu/2001/tours/nitrogen-need/index.html
Relationship between corn yield and most profitable N rate (72 site years)
Only 13 out of 72 site-years in IL required more than 1 lb of N per bushel
1 : 1 line
too high 82% of the time
Relationship between corn yield and most profitable N rate (72 site years)
1.2 : 1 line
too high 96% of the time
Why do some sites have lower optimal N rates?
Where does the N come from that enters a corn crop ?
Magdoff and Weil (2003)
N u
pta
ke (
lbs/
a)
Where does the N come from that enters a corn crop ?
A well-fertilized corn crop typically obtains more than half of its N from SOM
Why more N uptake?
Magdoff and Weil (2003)
N u
pta
ke (
lbs/
a)
Less N
tie-u
p !
What happens to fertilizer N ?
http://agronomyday.cropsci.uiuc.edu/2001/tours/n-fate/index.html
Measured after harvest
90
100
80 ?
What happens to fertilizer N ?
http://agronomyday.cropsci.uiuc.edu/2001/tours/n-fate/index.html
Measured after harvest
So how were the scientists able to track the fate of fertilizer N?
They used fertilizer spiked with N15!
90
100
80 ? Leaching,
denitrification, volatilization…
WHY??
≠
Timber soil Prairie soil
How much of Illinois was originally
covered by tall grass prairie ?
Old growth
forest in
How much of Illinois was originally
covered by forest ? Illinois once was
covered by a
complex mix of
prairie and forest
Prairie
dominated the
flat expanses
Forest
dominated the
hilly land
Info about inherent SQ
USDA Textural triangle
12 textural classes
http://www.oneplan.org/Images/soilMst/SoilTriangle.gif
Soil texture does not normally change with management.
What are these crazy people
doing ?
Location: Laurenburg, NC Date: 1961
Unsuccessfully
attempting to create
deep Midwest like
soils in the
Southeastern US
No
v/D
ec 2
01
1 is
sue
of
J o
f So
il an
d W
ater
Co
nse
rvat
ion
Are you familiar with the concept of tillage erosion?
Soil Changes After Sixty Years of Land Use in Iowa Jessica Veenstra, Iowa State University, 1126 Agronomy Hall, Iowa State University,
Ames, IA 50010
Soils form slowly, thus on human time scales, soil is essentially a non-renewable resource. Therefore in order to maintain and manage our limited
soil resources sustainably, we must try to document, monitor and understand human induced changes in soil properties. By comparing
current soil properties to an archived database of soil properties, this study assesses some of the changes that have occurred over the last 60 years,
and attempts to link those changes to natural and human induced processes. This study was conducted across Iowa where the primary land use has been row crop agriculture and pasture. We looked at changes in A
horizon depth, color, texture, structure, organic carbon content and pH.
Hill top and backslope landscape positions have been significantly degraded.
Catchment areas have deeper topsoil.
http://www.swcs.org/documents/filelibrary/BeyondTreport.pdf
NRCS SQ webpage
Keeping soil in place is only the beginning of soil conservation. Soil also has to function well. It must
hold nutrients and pesticides in place and keep them out of surface water. Soil must deliver
nutrients and water to plants as they need them. Soil should minimize the effects of floods and
droughts.
By addressing conservation issues from the perspective of soil quality instead of erosion, the
focus is on enhancing the soil as opposed to managing for tolerable degradation.
Have you observed the impact of management on your farm?
Soils from sites mapped as the same soil type but rated as high and low quality by farmers did not differ significantly with
respect to standard soil test parameters (P, K, Ca, Mg, pH). In contrast, most of the higher rated soils had higher levels of
OM, better structure and more biological activity.
Soil Respiration Test - indicates the soil's biological activity. Infiltration Test - measures the soil's ability to take in water.
Bulk Density Test - measures the soil's compaction or pore space. Electrical Conductivity (EC) Test - measures the salt concentration in the soil.
pH Test - measures the soil's acidity or alkalinity Soil Nitrate Test - measures the soil's nitrate levels
Aggregate Stability Test - measures the amount of water stable aggregates. Slake Test - estimates the stability of soil fragments in water
Earthworm Test - measures the number of earthworms in the soil Water Quality Tests estimates salinity and nitrate/nitrite levels in water
SQ tests in the tool box
Soil Quality is Not an End in Itself
The ultimate purpose of researching and assessing soil quality is not to achieve high
aggregate stability, biological activity, or some other soil property. The purpose is to protect
and improve long-term agricultural productivity, water quality, and habitats of all
organisms including people.
The effects of degraded soil quality are far reaching!
25 years of corn with
moldboard tillage
20 years of bluegrass sod followed by 5
years of corn with moldboard tillage
25 yrs of conventional corn
20 yrs of bluegrass, then 5 yrs conventional corn
Water stable aggregates
After adding water
Only 0.4% difference in OM
20 years of similar tillage and total organic input but different types of organic inputs
manure cover crops
crop residues crop residues
How do these soils differ ??
Rodale Institute Farming Systems Trial
Also less than 1% difference in OM
Contrasting stands of corn in the NC 9 tillage systems experiment
Continuous No-till
Fall plow/ spring disk
< 1%OM > 3%OM
Many soils in IL can take a lot of abuse !
Long term sod crop field
Physical changes are happening…
Same soil type – very different water holding capacity
But this much divergence is rare….
unless severe erosion has occurred
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 environmental problems
Pollution of water resources Loss of SOM
"But with the removal of water through furrows, ditches, and tiles, and the aeration of the soil by cultivation, what
the pioneers did in effect was to fan the former simmering fires of acidification and preservation into a blaze of
bacterial oxidation and more complete combustion. The combustion of the accumulated organic matter began to
take place at a rate far greater than its annual accumulation. Along with the increased rate of destruction
of the supply accumulated from the past, the removal of crops lessened the chance for annual additions. The age-old
process was reversed and the supply of organic matter in the soil began to decrease instead of accumulating."
William Albrecht – 1938 Yearbook of Agriculture
~50% ancient OM
~30% slowly decomposable OM
~20% active OM
5-10% OM
~75% ancient OM
~20% slowly decomposable OM
~5% active OM
2-5% OM
Long term no-till Intensive tillage
Ontario Ministry of Ag and Food
Does this profile contain
more SOM?
Clearly more OM
It is widely believed that soil disturbance by tillage was a primary cause of the historical loss of soil organic carbon (SOC) in North America, and that substantial SOC sequestration can be accomplished by changing from conventional plowing
to less intensive methods known as conservation tillage. This is based on experiments where changes in carbon storage have been estimated through soil
sampling of tillage trials. However, sampling protocol may have biased the results. In essentially all cases where conservation tillage was found to
sequester C, soils were only sampled to a depth of 1 foot or less…
Very few tillage studies have been sampled deeper than 1’
Many studies were only sampled ~6” deep!
Effect of tillage on microbial activity
Havlin et al. (1999)
+ SOM
Soil respiration in CT system
CT NT
Effect of tillage on microbial activity
Havlin et al. (1999)
+ SOM
Which tillage system has more microbial
activity ?
Soil respiration in NT system CT NT
Effect of tillage on microbial activity
Havlin et al. (1999)
+ SOM
Soil respiration in NT system CT NT
Which tillage system has more microbial activity when plants
can use the CO2?
Ecological Applications 2009
Increases in decay rates with N fertilization offset gains in carbon inputs to the soil in such a way that soil C sequestration was minimal in 78% of the systems
studied, despite up to 48 years of N additions.
The quantity of belowground organic inputs was the best predictor of long-term soil C storage. This indicates that, in these systems, in
comparison with increased N-fertilizer additions, selection of crops/cover crops with high root production is a more effective
management practice for increasing soil C sequestration.
Ecological Applications 2009
Increases in decay rates with N fertilization offset gains in carbon inputs to the soil in such a way that soil C sequestration was minimal in 78% of the systems
studied, despite up to 48 years of N additions.
Broadbalk continuous wheat experimentData modelled by RothC-26.3 (solid lines)
0
20
40
60
80
100
1820 1840 1860 1880 1900 1920 1940 1960 1980 2000 2020
Year
Organic C in soil
(t C ha-1) Farmyard manure annually
Unmanured
NPK
Why has the NPK program resulted in so little increase in SOM?
Soil
C (
ton
s/h
a)
unfertilized
Why does the system with the highest
residue production have the lowest OM
content?
This is an impressive accomplishment!
Acute root disease
Chronic root malfunction
vs.
= major cause of above ground deficiency symptoms
Root health – an excellent integrative indicator of SQ
Optimal root health requires more than the
latest BT trait, seed treatment or
drainage technology.
