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.

Table 1. Impact of the four driest years (April 1 to July 19) on corn grain yield at the Marshfield UW-ARS.
  GDUs 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

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