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

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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 2004 Days Later than Average
Silking July 20 July 25 5
Milk Aug 6 Aug 14 8
Dough Aug 18 Aug 31 13
Dent Aug 30 Sept 15 16
Mature Sept 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.

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 extra ordinarily high (and unexpected) 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. Full season hybrids are those that use or require the entire growing season to reach physiological maturity before fall frost. The relative maturity (RM) defined to be "full season" depends upon the area in the state and planting date. Once the RM for full season hybrids has been determined for the growing area and planting date, early maturity hybrids are those with lower RM ratings.

The yield to maturity relationship has usually been one-bushel higher yield and one-fourth point higher grain moisture for each one-unit increase in relative maturity. However, in recent years the yield difference with increased RM has been less than one bushel per RM unit. Grain yields and moisture contents from the University of Minnesota corn hybrid-testing program for the past five years were used to evaluate the effect of hybrid maturity on grain yield and kernel moisture content.

Table 2 presents the average yield for hybrids tested in maturity groups ranging from 91 relative maturity (RM) to 108 RM in southern Minnesota . The first Bu/RM figure on the bottom of the table is the bushels per RM unit relationship for each year through the entire range of maturties tested. The second Bu/RM line is the bushels per RM unit relationship up to RM of 105.

Except for 2002, there was less than one bushel per acre per RM unit for each of the past five years (averages 0.6 Bu/RM). However, there was a good relationship between yield and maturity through the maturity range up to 105 RM. The average relationship for the past five years was 1.1 bushels per RM up to 105.

Table 2. Yield Summary of Maturity Groups of Corn Hybrids Tested at Lamberton, Waseca and Plainview, 2000-2004.

2000 2001 2002 2003 2004
<97 169 169 169 145 203
98-102 176 176 178 149 216
103-105 179 178 189 152 207
>105 175 178 189 152 207
Bu/RM 0.44 0.51 1.54 0.59 0.09
Bu/RM* 1.26 0.79 1.56 0.47 1.24

*Yield and maturity relationship through RM of 105

The grain moisture relationship with hybrid maturity over the past five years is given in Table 3. For the maturity range up to 105 RM, kernels averaged 0.26 points higher in moisture content with each increase of one RM (average of the five years). So for southern Minnesota , there has been a good relationship of higher grain yields and higher moistures for hybrids up to 105 RM. The question then becomes one of economics. Is it more profitable to grow more corn that is wetter and pay the cost to dry it?

Table 4 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 0.26 points per RM unit, the energy cost to remove an extra 0.26 points of moisture from 100 bushels of corn is the value of 0.27 bushels of corn (0.26 times 1.05). If the expected average yield is 1.1 bushels per acre more per RM unit, then one can expect more profit potential by growing high yielding, full season hybrids. The average profit potential in this example is the value of 0.83bushels (1.1-0.27) at a yield level of 100 bushels per acre. For a 150 bushel yield level, the profit potential would be the value of 1.24 bushels per acre (0.83 x 1.5) for each RM unit up to 105 RM.

Table 3. Kernel Moisture Summary of Maturity Groups of Corn Hybrids Tested at Lamberton, Waseca and Plainview, 2000-2004.

2000 2001 2002 2003 2004
<97 15.5 20.7 19.6 16.3 19.7
98-102 16.4 21.1 20.7 17.8 21.4
103-105 17.4 21.4 21.3 18.7 22.5
>105 18.9 23.7 22.1 21.2 22.9
KM/RM 0.33 0.32 0.23 0.42 0.29
KM/RM* 0.24 0.26 0.22 0.33 0.25

*Kernel moisture and maturity relationship through RM of 105

This analysis of past corn performance test results shows that corn growers in Southern Minnesota can, on average, expect the best profits to occur by choosing the best yielding full-season hybrids with RM ratings of close to 105. And there may be areas in the very south tier of counties that full season could be as high as 110RM. 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.

Table 4. 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
1 2.5 5
  - -
- - - - - - - - - Bu/A - - - - - - - - -
100 1.05 2.63 5.25
125 1.31 3.28 6.56
150 1.58 3.94 7.88
175 1.84 4.59 9.19
200 2.10 5.25 10.50

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