December 2006
Field Crops 28.5 - 45
The Relationship between Corn Grain Yield and Forage Yield:
Effect of Moisture, Hybrid and Environment
Joe Lauer, Corn Agronomist
PDF Version
Summary
- Arriving at a fair and equitable price for corn silage is difficult due to the number
of factors involved that are dynamic and biologically variable.
- Grain equivalents are quite variable to the extent that one predetermined value
should not be used in contracts between growers and dairyman.
Understanding the relationship between corn grain and forage yield is important
to dairymen and grain farmers who often contract with each other for corn silage
production. Recently, the grain versus forage relationship has been used to set
government Loan Deficiency Payments (LDP) to farmers for corn silage acres. Arriving
at a fair and equitable price for corn silage is difficult due to the number of
factors involved that are dynamic and biologically variable. Some growers will want
to calculate the forage price based on corn grain yield (as the alternative harvestable
crop) and some dairymen will want to calculate the price based on alternative forages
(primarily alfalfa as the alternative forage source). In either case, the final
price is affected by supply and demand of corn grain within a region.
The objective of this paper is to describe the relationship between grain and forage
yield. For the growing seasons between 1997 and 2005, experiments were conducted
to measure the impact of hybrid, plant density, planting date and row spacing on
corn performance. It is difficult to obtain data for both corn grain and forage
yield as usually one or the other is harvested in a field or research plot situation.
In these studies, forage yield and quality was measured in four of eight rows in
the plot. The four remaining rows were left for later grain yield and quality measurements.
The relationship between grain yield and forage yield
The relationship between grain yield and forage yield is shown in Figure 1. Little
grain yield was measured when forage yields were below 2 to 3 tons dry matter per
acre. The relationship between grain yield and forage yield was mostly linear through
forage yields of 8 tons dry matter per acre.
To calculate the value of an acre of corn silage, the amount of grain contained
in one ton of silage (grain equivalent) is multiplied by the corn price and the
forage yield. For example, if corn yielded 150 bushels/A and was 65% moisture, the
grain equivalent is 7.5 bushels of grain per ton of corn silage (Table 1). An average
yield is 20.4 T/A. If corn is priced at $2.00 per bushel, the value of the field
is 7.5 bu/T x $2.00 /bu x 20.0 T/A = $300/A or $15 /T. Further negotiation would
need to be conducted over harvest, ensiling, and storage costs.
Factors that affect the grain equivalent calculation
Anything that affects grain or forage yield will affect grain equivalents contained
in corn forage. Depending upon grain yield level, grain equivalents per ton of corn
silage ranged from 3.6 to 7.5 bushels per ton of silage at 65% moisture (Table 1).
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Table 1. Bushels of grain contained in a ton of corn silage. Values are derived from
experiments conducted in Wisconsin between 1997 and 2005.
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0% moisture
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60% moisture
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65% moisture
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70% moisture
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Grain yield @ 15.5% moisture
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Silage yield
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Grain equivalent per ton of silage
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Silage yield
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Grain equivalent per ton of silage
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Silage yield
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Grain equivalent per ton of silage
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Silage yield
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Grain equivalent per ton of silage
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Bu/A
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T/A
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Bu/T
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T/A
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Bu/T
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T/A
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Bu/T
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T/A
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Bu/T
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25
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2.4
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24.9
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6.0
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4.1
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6.9
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3.6
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8.0
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3.1
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50
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3.2
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24.1
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7.9
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6.3
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9.1
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5.5
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10.6
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4.7
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75
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4.0
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23.3
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10.0
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7.5
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11.4
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6.6
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13.3
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5.7
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100
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4.9
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22.4
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12.2
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8.2
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13.9
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7.2
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16.2
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6.2
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125
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5.9
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21.5
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14.6
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8.5
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16.7
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7.5
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19.5
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6.4
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150
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7.0
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20.3
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17.5
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8.6
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20.0
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7.5
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23.3
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6.4
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175
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8.4
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19.0
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20.9
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8.4
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23.9
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7.3
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27.9
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6.3
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200
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10.2
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17.1
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25.6
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7.8
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29.3
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6.8
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34.1
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5.9
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The amount of moisture has a major influence on this relationship and needs
to be considered to accurately determine fair silage prices. Grain yield per ton
of silage for four moisture levels is shown in Table 1. For a field that yields
150 bu/A, the grain equivalents range from 20.3 bu/T at 0% moisture to 6.4 bu/T
at 70% moisture.
Environment can significantly affect the amount of grain in corn silage.
This year’s (2006) drought affected pollination reducing both grain yield and plant
stature. Last year’s (2005), drought reduced plant stature, but grain yields were
at record levels. Following the 2005 growing season, farmers would sometimes talk
about corn silage being ‘hot’ when fed to livestock, meaning that there was too
much grain compared to stover (grain equivalents) in the silage.
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Table 2. Year effect on grain equivalents contained in corn silage at ArlingtonWI.
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Grain yield equivalent
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Year
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50
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100
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150
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200
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R2
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bushels of grain (15.5%) per Ton of corn silage (65% moisture)
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2005
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9.0
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8.3
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8.0
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7.9
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0.65
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2004
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3.2
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5.4
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6.8
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6.9
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0.74
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2003
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12.4
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7.9
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7.0
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6.7
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0.34
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2002
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---
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---
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7.7
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7.3
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0.39
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2001
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3.1
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5.5
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7.2
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8.0
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0.42
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2000
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4.2
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6.6
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7.6
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---
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0.50
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1999
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2.8
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5.0
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6.6
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6.9
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0.37
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1998
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2.7
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4.9
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6.4
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7.2
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0.35
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1997
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7.1
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9.1
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9.2
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---
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0.51
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The growing environment affects the relationship between grain and forage yield.
Depending upon year, grain equivalents ranged from 6.4 to 9.4 at a 150 bu/A yield
level (Table 2 and 3). Due to the drought in 2005, many cornfields are shorter than
normal but corn yield appears to be high. If this observation holds true and grain
yield is relatively greater than forage yield, grain equivalents will be higher
than normal.
In 2004 and 2005, six corn hybrids were grown at six locations. Hybrid types included
bmr, leafy, transgenic, and normal hybrids. Each hybrid was replicated 3 times and
grown in 8-row plots, with 4 rows used for silage harvest, and 4 rows used later
at grain harvest.
Table 3. Location and year effect on grain equivalents (bu/T) contained in corn silage
for
six corn hybrids.
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Location
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Year
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Average
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Minimum hybrid
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Maximum hybrid
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bushels of grain (15.5%) per Ton of corn silage (65% moisture)
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Arlington
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2004
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7.7
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6.5
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8.3
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|
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2005
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8.6
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7.8
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10.5
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Fond du Lac
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2005
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7.0
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6.0
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7.5
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Galesville
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2004
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7.2
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5.8
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8.2
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|
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2005
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8.0
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7.0
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8.8
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Marshfield
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2004
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7.0
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5.5
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7.7
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|
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2005
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6.3
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4.5
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7.2
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Rhinelander
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2005
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7.7
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6.7
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10.3
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Valders
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2004
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7.8
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7.0
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8.2
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|
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2005
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7.5
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6.5
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8.0
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Average
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---
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7.5
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6.4
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8.5
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Table 4. Trait effect on grain equivalents (bu/T) contained in corn silage hybrids
(2004-2005).
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Traits
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Bushels of grain (15.5%) per Ton
of corn silage (65% moisture)
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None
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7.8
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BMR
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6.7
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CB,LL
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7.6
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LSD(0.05)
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0.9
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On average, hybrids across locations and years produced grain equivalents of 7.5
bu/T (Table 3). The range among environment averages was 2.3 bu/T (min.= 6.3 bu/T,
max.= 8.6 bu/T). The range among hybrids for grain equivalents was 6 bu/T (min.=
4.5 bu/T, max.= 10.5 bu/T). Grain equivalents tended to be higher at Arlington and
Galesville in 2005 (drought early) than 2004 (normal). The average range among hybrids
for an environment was 2.1 bu/T (max.= Rhinelander 2005= 3.6 bu/T, min.= Valders
2004= 1.2 bu/T). Brown mid-rib hybrids had significantly lower grain equivalents
than Normal or Bt-ECB transgenic hybrids (Table 4).
Forage moisture, hybrid and environment significantly affect grain equivalents and
must be considered when negotiating a contract. Ideally, contracts should be based
on corn silage quality rather than grain equivalents. Dairymen and corn farmers
need to understand the grain equivalent relationship when acres are contracted for
silage production. This relationship is dynamic and, as we are learning, quite variable
to the extent that one predetermined value should probably not be used in contracts.