This document discusses optimal nitrogen rates for corn production. It summarizes research from over 40 trials conducted over 3 years that found optimal nitrogen rates averaged slightly less than 1 pound per bushel of corn, with a range of almost none to 1.2 pounds per bushel. The research also found relatively high corn yields without any supplemental nitrogen application. The highest optimal nitrogen rates were typically associated with the lowest yielding environments. The document explores where corn obtains its nitrogen from and what happens to fertilizer nitrogen after application. It discusses factors that influence optimal nitrogen rates between sites.

1. Soil Quality
Should you be concerned?
Dr. Joel Gruver
WIU Agriculture
j-gruver@wiu.edu

2. 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

3. 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

4. Relationship between corn yield
and most profitable N rate (72 site years)
too high 96%
of the time
1.2 : 1 line

5. Why do some sites have lower optimal N rates?

6. Where does the N come from that
enters a corn crop ?
N uptake (lbs/a)
Magdoff and Weil (2003)

7. A well-fertilized the N come fromobtains
Where does corn crop typically that
more enters a corn crop ? SOM
than half of its N from
N uptake (lbs/a)
Less N tie-up !
Why
more N
uptake?
Magdoff and Weil (2003)

8. What happens to fertilizer N ?
100
90
80 ?
Measured after harvest
http://agronomyday.cropsci.uiuc.edu/2001/tours/n-fate/index.html

9. What happens to fertilizer N ?
100
So how were the scientists able to Leaching,
90
80
track the fate of fertilizer N?
They used fertilizer spiked with N15!
?
denitrification,
volatilization…
Measured after harvest
http://agronomyday.cropsci.uiuc.edu/2001/tours/n-fate/index.html

10. WHY??

11. Timber soil Prairie soil
≠

12. How much of Illinois was originally
Illinois once wascovered by forest ?
covered by tall grass prairie ?
covered by a
complex mix of
prairie and forest
Prairie
dominated the
Old growth
flat expanses
forest in
Forest
dominated the
hilly land

15. Info about inherent SQ

17. Soil texture does not normally change with management.
USDA 12
Textural textural
triangle classes
http://www.oneplan.org/Images/soilMst/SoilTriangle.gif

18. What are these
crazy people
doing ?
Location:
Laurenburg, NC
Date: 1961
Unsuccessfully
attempting to create
deep Midwest like
soils in the
Southeastern US

19. Nov/Dec 2011 issue of J of Soil and Water Conservation

20. Are you familiar with the concept of tillage erosion?

21. 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.

22. http://www.swcs.org/documents/filelibrary/BeyondTreport.pdf

23. NRCS SQ webpage

24. 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.

25. Have you observed the impact of management on your farm?

26. 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.

28. SQ tests in the tool box
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

30. 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.

31. The effects of degraded soil quality are far reaching!

32. 20 years of
25 years of bluegrass sod
corn with followed by 5
moldboard years of corn with
tillage moldboard tillage

33. After adding water
Water stable
aggregates
25 yrs of Only 20 yrs of bluegrass, then 5
0.4%
conventional corn yrs in OM
difference conventional corn

34. How do these soils differ ??
manure
cover crops
crop residues crop residues
Also less than 1%
difference in OM
20 years of similar tillage and total organic input
but different types of organic inputs
Rodale Institute Farming Systems Trial

35. Contrasting stands of corn in the NC 9 tillage systems experiment
> 3%OM < 1%OM
Continuous Fall plow/
No-till spring disk

36. Many soils in IL can take a lot of abuse !

37. Physical changes are happening…
Long term sod crop field
Same soil type – very different water holding capacity

38. But this much divergence is rare….
unless severe erosion has occurred

39. Artificial drainage has greatly increased the number of days
when soils in the Upper Midwest are suitable for field
operations
but has also
contributed
Pollution of to environmental
water resources problems Loss of SOM

40. "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

41. 5-10% OM
~50% ancient OM
~30% slowly decomposable OM
~20% active OM

42. 2-5% OM
~75% ancient OM
~20% slowly decomposable OM
~5% active OM

43. Long term no-till
Intensive tillage
Clearly more OM
Does this
profile
contain
more SOM?
Ontario Ministry of Ag and Food

44. 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…

45. Many studies were only sampled ~6” deep!
Very few tillage studies have been sampled deeper than 1’

46. Effect of tillage on microbial activity
+ SOM
CT
NT Soil respiration in CT system
Havlin et al. (1999)

47. Effect of tillage on microbial activity
+ SOM
Which tillage system
has more microbial
activity ?
CT Soil respiration in NT system
NT
Havlin et al. (1999)

48. Effect of tillage on microbial activity
+ SOM
Which tillage system
has more microbial
activity when plants
can use the CO2?
CT Soil respiration in NT system
NT
Havlin et al. (1999)

50. Ecological Applications 2009
The quantity of belowground organicN fertilizationbest predictor of
Increases in decay rates with inputs was the offset gains
long-term soil C storage. the soil in such ain these systems,C
in carbon inputs to This indicates that, way that soil in
comparison with increased N-fertilizer additions, selection of
crops/cover crops with high root productionof a more effective
sequestration was minimal in 78% is the systems
management practice for increasing soil CN additions.
studied, despite up to 48 years of sequestration.

51. 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.

52. Broadbalk continuous wheat experiment
Data modelled by RothC-26.3 (solid lines)
100
Organic C in soil
(t C ha-1) Farmyard manure annually
80
Soil C (tons/ha)
60
Why has the NPK program resulted in
so little increase in SOM?
40
NPK
20 unfertilized
Unmanured
0
1820 1840 1860 1880 1900 1920 1940 1960 1980 2000 2020
Year

53. Why does the system
with the highest
residue production
have the lowest OM
content?

54. This is an impressive accomplishment!

56. Acute root
disease
vs.
Chronic root
= major cause of above ground deficiency symptoms
malfunction

57. Root health – an excellent integrative indicator of SQ
Optimal root
health requires
more than the
latest BT trait, seed
treatment or
drainage
technology.