The "Million Dollar" Rain
July 21, 2005 12(20):159-161
Joe Lauer, Corn Agronomist
On July 19, I drove from Madison to Fond du Lac to LaCrosse (Galesville) to Madison
inspecting plots in the UW corn trials. Windshield survey of the corn I passed along
the way was discouraging. My tally showed nearly 80% of the fields with leaf rolling
in over half of the field. Most of the fields were uneven and had tassels struggling
to emerge. Some fields were brown and seemed killed, although upon closer inspection
the whorl still had four to six leaves and a tassel that was turgid. Counties most
affected included Dane, Columbia, Dodge, Green Lake, Marquette, Adams, Juneau, Monroe,
LaCrosse and Sauk counties. Areas with some stress (lower leaves firing but fields
tasseling evenly) were western Fond du Lac, southern Trempealeau, Vernon and western
Richland counties. The best-looking corn was in Vernon County.
As I sit and write this article, a significant rain shower is falling and radar
shows that the system has passed over much of the area I traveled yesterday. The
Arlington ARS received about 1 inch. It is truly one of those "million dollar"
rains that will get the corn crop through part of the pollination phase of its life
cycle. Nevertheless, we need to continue to have these 1-inch rains each week for
the next 8 weeks. Most of the soil water has been used by the corn plant. Following
pollination, the corn plant will not be producing much new root growth and all of
its energy from photosynthate will be going towards grain production and filling
kernels.
I had a number of calls about a previous article titled "Will History Repeat
Itself?" The basic question was, "If precipitation would return to normal,
could the corn crop recover?" In the article, I had summarized data for Arlington.
Below is a similar table for the UW-ARS farm at Marshfield. Again, I used the five
driest years since 1950 for the period between April 1 and July 19. A rolling average
of yields in the UW Corn Trials was calculated using the 3-yrs prior and the 3-yrs
following the year of interest. Average yields of each year were compared to the
6-yr rolling average.
During years with dry periods between April 1 and July 19, grain yield decreased
in 3 of 4 years compared to the rolling average. In only one year, 1987, was grain
yield similar to the rolling average and that might be due to the poor yields in
years used to calculate the rolling average. Like Arlington, I think we can expect
yields to be 0 to 25% lower this year given the stress that has occurred. One management
factor working in our favor was the earlier than normal planting season of 2005.
The crop may have had enough soil moisture to begin pollination and this rain will
allow it to complete this important period of its life cycle.
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Table 1. Impact of the four driest years (April 1 to July 19) on corn grain yield
at the Marshfield UW-ARS.
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|
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GDUs
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Precipitation
|
|
UW Corn Hybrid Trials
|
|
Year
|
April 1 to
July 19
|
April 1 to
July 19
|
July 19
to frost
|
|
Planting
date
|
Harvest
date
|
Number of
hybrids
|
Average
yield
|
6-yr rolling
average yield
|
Yield
impact
|
|
|
|
inches
|
inches
|
|
|
|
|
Bu/A
|
Bu/A
|
%
|
|
2005
|
1372
|
7.4
|
---
|
|
May 3
|
---
|
142
|
---
|
---
|
---
|
|
1988
|
1561
|
7.5
|
7.9
|
|
May 6
|
Oct. 11
|
126
|
99
|
131
|
-24
|
|
1995
|
1372
|
7.5
|
11.6
|
|
May 5
|
Oct. 17
|
162
|
130
|
152
|
-14
|
|
1987
|
1580
|
8.1
|
9.3
|
|
Apr. 29
|
Oct. 19
|
124
|
126
|
122
|
3
|
|
1983
|
1174
|
8.2
|
12.6
|
|
May 11
|
Oct. 27
|
108
|
77
|
103
|
-25
|