Performance tests are essential resources for selection of the best crop genetics. When using performance tests to select corn hybrids, producers often use yield as the sole criteria for choosing hybrids they will plant. However, choosing on yield alone does not always result in selection of the most profitable hybrids.
Corn is typically harvested at moisture levels above that needed for safe storage (15.5%) and dried with artificially-heated air. There are two costs associated with drying corn to moisture levels for safe storage. The most obvious is the cost of the fuel, electricity, equipment and facilties needed to dry the grain. A less obvious cost is the weight loss that occurs as moisture leaves the grain during the drying process. This weight loss from drying is called "shrink" and is expressed as a percentage of the original amount of corn before it is dried. Shrink can be subdivided in water shrink and handling loss. Water shrink is loss of the weight of the water and is typically 1.183% for each percentage point of moisture removed when drying corn to 15.5% moisture. Handling loss is the grain lost from handling during drying and is generally estimated as 0.5%. The publication at the following link contains more detailed information on calculating grain weight shrinkage in corn due to mechanical drying - http://www.extension.iastate.edu/Publications/NCH61.pdf.
The most profitable hybrids will have relatively high grain yields, but will also have low drying costs and shrinkage (i.e. low harvest moisture). Later-maturing hybrids tend to have greater yields than early-maturing hybrids, but also have relatively greater harvest moisture. The most profitable hybrids will be those with the right balance of grain yield and harvest moisture. This balance changes with grain price and drying cost. Due to the importance of harvest moisture in determining profitibility of corn production, the Iowa Corn Performance Test contains adjusted gross value data for each hybrid.
Adjusted gross value is calculated as follows in the Iowa Corn Performance Test:
Problem 1
The unadjusted (wet) yield for a hybrid is 205.0 bu/a and the harvest moisture was 19.9%. What is the adjusted gross value for this hybrid at 15.5% moisture with a price of $3.25 per bushel, and drying costs of $0.05 per point of moisture per bushel
Water shrink = 1.183 x (19.9 -15.5) = 5.2052
Total shrink = 5.2052 + 0.5 = 5.7052
Dry yield = ((100- 5.7052)/100) x 205 bu/a = 193.3 bu/a
Gross value = 193.3 bu/a x $3.25 = $628.23
Drying cost = 205.0 bu/a x (19.9 -15.5) x $0.05 = $45.10
Adjusted gross value = $628.23 – $45.10 = $583.13
Which of the following two hybrids has the greater gross adjusted value? Assume you are drying to 15.5% moisture, corn price = $3.25/bu, and drying cost = $0.05 per point per bushel.
Hybrid 1: Yield = 179.5 bu/a, moisture = 22%
Hybrid 2: Yield = 170.4 bu/a, moisture = 17%
Adjusted gross value for hybrid 1
Water shrink = 1.183 x (22.0 -15.5) = 7.6895
Total shrink = 1.7745 + 0.5 = 8.1895
Dry yield = ((100- 8.1895)/100) x 179.5 bu/a = 164.8 bu/a
Gross value = 164.8 bu/a x $3.25 = $535.60
Drying cost = 179.5 bu/a x (22.0 -15.5) x $0.05 = $58.34
Adjusted gross value = $535.60 – $58.34 = $477.26
Adjusted gross value for hybrid 2
Water shrink = 1.183 x (17.0 -15.5) = 1.7745
Total shrink = 1.7745 + 0.5 = 2.2745
Dry yield = ((100- 2.2745)/100) x 170.4 bu/a = 166.5 bu/a
Gross value = 166.5 bu/a x $3.25 = $541.13
Drying cost = 170.4 bu/a x (17.0 -15.5) x $0.05 = $12.78
Adjusted gross value = $541.13 – $12.78 = $528.35
Hybrid 2 has the greater adjusted gross value. It has lower yield than hybrid 1, but its lower harvest moisture resulted in a greater adjusted gross value.