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Minnesota Crop News > 2001-2008 Archives
June
13, 2005
Nitrogen
Status of Corn Fields
George
Rehm
Department of Soil, Water, and Climate
Once again, excessive rainfall is raising questions about
N loss and management practices that might be used to overcome
this potential loss. This potential loss has also been
a concern in other years in the recent past. We can learn
from the past; but, no two years are the same.
Until the week of June 6, most of the rainfall throughout
the state was not extremely heavy—it just seemed
to rain every day. Certainly, there were fields where the
water ponded and corn emergence was reduced substantially.
For these areas, replanting, rather than N loss, will be
the major consideration.
In recent years, there has been a switch in N application
from preplant to sidedress timing for sandy soils. Since
most sidedress N has not been applied to these sandy soils,
N loss is not yet a serious concern.
For the remainder of the fields, there is a concern about
loss. Until the week of June 6, soil temperature in many
of the wet fields was low. These cool temperatures should
have minimized losses due to denitrification. In addition,
it is not possible to accurately predict N and dentrification
losses by analysis of soil samples. So, a soil sampling
approach as a management tool is not suggested at this
time.
In other years, a scoring system was used to predict
the need for addition N during the growing season. In June
of 2004, this scoring system was applied to several fields
with an additional 40 to 50 lb. N per acre recommended.
Most reports during the winter from growers who used additional
N indicated a positive yield increase from the supplemental
N. The reported yield increases ranged from 5 to 15 bu.
per acre.
So, rather than using soil testing in 2005, use of the
scoring system is suggested. This scoring system relies
heavily on plant appearance and color. That score sheet
follows.
| When and how was the N applied? |
a) In the fall, less than 4 inches deep and soil
temperatures were above 50°F |
6 |
b) In the fall, 4 or more inches
deep and soil temperatures were above 50°F
|
5 |
c) In the fall, above 4 inches
with N-Serve and soil temperatures above 50°F
|
4 |
d) In the fall, below 4 inches
with N-Serve and soil temperatures below 50°F
|
3 |
e) In early spring (end of March
or in April)
|
3 |
f) Broadcast on the soil surface
in the fall with no incorporation
|
4 |
g) Broadcast on the soil surface
followed by incorporation 50°F
|
3 |
h) In May followed by incorporation
|
2 |
| What was the predominate
spring (May) soil condition? |
a) Normal or drier than normal
|
1 |
b) Wetter than normal
|
3 |
c) There was standing water in
the low areas
|
4 |
| How does the
crop look? |
a) Taller than 12-16 inches, showing N deficiency*
|
5 |
b) Shorter than 12-16 inches, showing
N deficiency*
|
3 |
c) Shorter than 12-16 inches, showing
no N deficiency*
|
2 |
d) Taller than 12-16 inches, green
|
1 |
*Corn that shows N deficiency has an overall light green
color and frequently the leaves show some striping. The
first true leaf will usually have a yellow V along the
midrib. The point of the V will be near the plant and not
at the tip of the leaf.
To determine the need for supplemental N, add the scores
for the answer to each question. If the score is 7 or less,
supplemental N will probably not be needed. With a score
of 10 or more, supplemental N is suggested. A rate of 40
to 50 lb. N per acre is suggested. This should be knifed
in or incorporated in some way, if possible. A score of
8 or 9 falls into a gray area and requires a second evaluation.
Wait 3 to 4 days and evaluate again. The appearance of
the corn plant changes rapidly at this time of the year.
The evaluation should take place before the window for
sidedress application is closed.
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