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A review of the 2004 growing season and corn hybrid maturities for 2005 in central and northern Minnesota

D.R. Hicks, Agronomy and Plant Genetics, University of Minnesota

The cold and wet growing season for Minnesota delayed the growth and development of corn such that growers may consider selecting earlier maturing hybrids for 2005 compared with maturities that they have normally been growing. The subject of this newsletter is to evaluate the yield and drying cost tradeoffs of planting earlier maturing corn hybrids.

Normal Corn Development Compared With 2004
Calendar dates for developmental events for corn in Minnesota for the past five years compared with this past year are given in Table 1.
Table 1. Calendar dates when 50% of Minnesota corn acreage reached various stages of corn grain development for the past five years and for 2004.

Growth Stage 5 Year Average 2004Days Later than Average
SilkingJuly 20 July 25 5
MilkAug 6 Aug 14 8
DoughAug 18 Aug 31 13
DentAug 30 Sept 15 16
MatureSept 19 Oct 6 17

Corn this year silked five days later than the average date of the past five years, even though corn planting in general was earlier than the past five-year average. But the cold May, June, and July delayed the average silking date by five days. The continued lower than normal heat unit accumulation for August further delayed corn reaching the milk, dough, and dent stages. The 50% above normal heat unit accumulation during September moved the crop toward maturity, but less than 40% of the crop reached normal physiological maturity before the final killing frost of October 2; most of the 60% that did not reach full maturity was in central to northern Minnesota .
The grain filling period from July 20 to September 19 for the past five-year average is 61 days. This year, there were 74 days during the grain filling period between July 25 and October 6. The extra 13 days for grain filling was certainly a major factor in producing some of the excellent yields that occurred. But the maturity date was later than normal, which left less field drying time and pushed harvest later into October and November. As a result, corn growers may consider buying earlier maturing hybrids to grow in 2005.
Maturity Relationship with Grain Yield and Kernel Moisture
Highest yields are usually achieved by planting high yielding hybrids that are full season for any location. The yield to maturity relationship has usually been about one bushel higher yield for each one-unit change in relative maturity. Average grain yields and kernel moisture contents from the University of Minnesota corn hybrid-testing program for central and northern Minnesota are given in Tables 2 through 5 to examine the yield and moisture relationship with hybrid maturity.
Table 2. Yield Summary of Maturity Groups of Corn Hybrids Tested at Rosemount and Morris, 2000-2004.


For each year, the average yield is given for hybrids tested in maturity groups ranging from 90 relative maturity (RM) to 105 RM. The BU/RM figure on the bottom of Table 2 is the bushels per relative maturity unit relationship for each year. In 2000, grain yields increased 0.9 bushel with each one increase in RM. The yield to maturity relationship in 2001 was an increase of 1.37 bushels per RM. There was no relationship in 2002; that is, early hybrids yielded as well as full season hybrids. And the early hybrids yielded higher than full season hybrids for both 2003 and 2004. This would have been expected in 2004; in a cold season the early hybrids have a better chance to reach full maturity and thus develop their yield potential which would not be the case for full season hybrids. The average change in yield for each RM unit over the past five years is 0.02 which means that on average, early hybrids yield as well as full season hybrids in central Minnesota .
Table 3. Kernel Moisture Summary of Maturity Groups of Corn Hybrids Tested at Rosemount and Morris, 2000-2004.


The average kernel moistures for each RM group are given in Table 3 for each year. Kernel moisture content was consistently higher with increases in RM of hybrids. The change in kernel moisture with each one increase in RM is given on the bottom line of table 2 and averages 0.35 for the past five years. Higher moisture content means more time is necessary for field drying or there is an extra cost of drying the wetter grain. So for the central part of Minnesota, it appears that the highest yielding early hybrids represent the best potential for corn profitability, so growers should be seeking the highest yielding hybrids with maturity ratings of less than 95RM.
Similar data are given for the northern test locations in Tables 4 and 5 for grain yield and moisture for hybrid maturity groups.
Table 4. Yield Summary of Maturity Groups of Corn Hybrids Tested at Rothsay and Staples, 2000-2004.


Full season hybrids yielded significantly higher than did earlier hybrids in years 2001, 2002, and 2003. And as expected in 2004, the cold season favored early hybrids rather than full season hybrids. For the five years, the yield to maturity relationship averaged 1.2 bushels per RM unit through the maturity range of 75 to 95 RM.
Table 5. Kernel Moisture Summary of Maturity Groups of Corn Hybrids Tested at Rothsay and Staples, 2000-2004.


Kernel moisture is always higher as hybrids are grown with higher RM ratings. The average relationship for the past five years has been an increase in kernel moisture of 0.28% with each one increase in RM rating.
For northern Minnesota grain yields are generally higher with the more full season hybrids, but grain is wetter, so the cost to dry the grain needs to be considered. Table 6 gives the energy cost, expressed in bushels per acre, to remove 1 to 5 points of moisture from yield levels ranging from 100 to 200 bushels per acre. The energy cost to remove 1 point of moisture from 100 bushels of corn is equal to the value of 1.05 bushels using a LPgas price of $1/gal and a corn selling price of $2/bushel. Since the moisture content of kernels increases by an average of 0.28 points per RM unit, the energy cost to remove an extra 0.28 points of moisture from 100 bushels of corn is the value of 0.29 bushels of corn (0.28 times 1.05). If the expected average yield is 1.2 bushels per acre more per RM unit, then one has more profit potential for growing high yielding more full season hybrids. The average profit potential is the value of 0.91 bushels (1.2-0.29) at a yield level of 100 bushels per acre.
Table 6. Bushels of Corn Required to Pay the Energy Costs to Remove 1 to 5 Points of Moisture, LPgas $1/gal and Corn Price of $2/Bu).

of Moisture to Remove
 - -
- - - - - - - - - Bu/A - - - - - - - - -

This analysis of past corn performance test results shows that corn growers in Central Minnesota can, on average, expect the best profits to occur by choosing the best yielding hybrids with RM ratings of 90 to 95 and earlier. But, growers in the northern corn-growing zone of Minnesota should choose high yielding hybrids with RM ratings that are full season for the area (70 in the far north to 85 in the Moorhead area). Grain will be higher in moisture content, but the energy cost to dry the extra moisture is less than the value of the extra yield obtained from the full season hybrids.

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