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Corn: Hybrid Selection
Excerpt from Agronomy Guide for Field Crops (Chapter 3)Order OMAFRA Publication 811: Agronomy Guide for Field CropsTable of Contents
Maturity RatingsCorn development is driven primarily by temperature, and this is especially true during the planting-to-silking period. Unlike soybeans, day length has little effect on the rate at which corn develops. The Ontario Crop Heat Unit System has been developed to calculate the impact of temperature on corn development. Ontario crop heat units (CHUs) are calculated based on daily maximum and minimum temperatures and allow for a numerical rating of growing seasons, geographical locations and corn hybrids. This system allows growers to select hybrids with CHU ratings that have a high probability of reaching maturity before a killing frost. Table 3-7. Average Seasonal Accumulations of Crop Heat Units From Various Sites Across Ontario, outlines the accumulated crop heat units over the course of an average growing season at various locations across Ontario. | Top of Page | Source: A. Bootsma, Agriculture and Agri-Food Canada, and D.M. Brown, University of Guelph. 1The season start date (date to start accumlating CHUs)
is determined as: (1) the last day of three consecutive days, with
daily mean air temperatures equal to or greater than 12.8°C (55°F);
and (2) the starting date for this three-day period each year occured
after the date the 30-year average daily mean air temperature reached
10°C (50°F) in the spring for each weather station site. Source: A. Bootsma, Agriculture and Agri-Food Canada, and D.M. Brown, University of Guelph. 1The season start date (date to start accumlating CHUs)
is determined as: (1) the last day of three consecutive days, with
daily mean air temperatures equal to or greater than 12.8°C (55°F);
and (2) the starting date for this three-day period each year occured
after the date the 30-year average daily mean air temperature reached
10°C (50°F) in the spring for each weather station site. | Top of Page | Producers who record high and low temperatures can use Table 3-8. Daily Crop Heat Unit Accumulations Based on Maximum and Minimum Temperatures, to calculate CHUs for their own farm. Other jurisdictions use different systems for quantifying the effect of temperature on corn development and for rating corn hybrid maturity. Unfortunately, these systems are unique, and true mathematical conversions from one to the other are not possible. Table 3-9. Approximate Conversions Between Three Systems of Measuring Heat Accumulation in a Growing Season, provides values to assist in making reasonable comparisons between the different systems. | Top of Page | Selecting the Most Profitable HybridsHybrid selection is probably the single most important management decision in determining cropping profitability. Corn hybrids with superior yielding potential have been continuously introduced into the market place over the past 40 years. Yield increases of approximately 1.5% per year have been occurring. To remain competitive, growers must introduce new hybrids to their acreage on a regular basis. The following are a few key considerations: Maturity and CHUsUsing crop heat unit ratings, select hybrids that will reach maturity (black layer) before season-ending frosts traditionally occur in your area. Table 3-7. Average Seasonal Accumulations of Crop Heat Units From Various Sites Across Ontario, Figure 3-1. Crop Heat Units Available for Corn Production, or farm records will provide the heat units normally accumulated in a given area. For example, for someone living near Brucefield, the long-term data from Table 3-7. Average Seasonal Accumulations of Crop Heat Units From Various Sites Across Ontario indicates heat unit accumulation averages 2,823 CHUs. Notice that the average start date for CHU accumulation is May 16. If a grower has the ability to plant early, where emergence can be expected before May 16, consider selecting a hybrid with a heat unit rating 100-150 CHUs higher than the full season (2,800) recommendation. Note that by the end of May, 2 weeks later, 230 heat units have usually been accumulated. If planting has not occurred by this date, selecting a lower heat unit hybrid is recommended (see the section Switch Dates).Figure 3-1. Crop Heat Units Available For Corn Production
This map is based on weather data from 1961-90. The average crop heat unit value will be reached 50% of the time. | Top of Page | Highest YieldIn any given hybrid performance trial, there may be a 1.88-2.50 t/ha (30-40 bu/ac) difference in yield between the highest- and lowest-yielding hybrids. This emphasizes the importance of obtaining reliable information on hybrid yield potential and adaptability. Growers must be able to sort out information from two main sources: performance trial data and strip trial data. The Ontario Corn Committee conducts corn hybrid performance trials each year across the province. These performance trials include the majority of available hybrids. Generally, these trials are set up so that a given set of hybrids, for a certain heat unit range, are tested at three to four locations. These trials give a good indication of yield potential but because they are limited to a few locations, do a poor job of indicating hybrid adaptability over a wide range of conditions. For this sort of data, growers need to turn to strip trials that are conducted on a larger number of sites across a wide range of environments. Seed companies usually summarize these strip trials. Many growers find it valuable to have a corn hybrid strip trial on their own farm. This allows new, high-yielding potential hybrids to be tested against those proven performers in the farming practice. However, it is important to remember that reliable hybrid selections require more than one test site even if that site is on the grower’s own farm. Growers should look for 2-year data that originate from many sites (preferably more than 30) before making decisions about hybrids that will be planted on a significant portion of their acreage. Never purchase a hybrid without consulting performance data. The Ontario Corn Committee publishes the Hybrid Performance Trial Report each December. This information is also available on the Internet at the Ontario Corn Producers Web site at www.ontariocorn.org. Strip trials results from many seed companies are also being compiled by the Ontario Soil and Crop Improvement Association on their Web site at www.ontariosoilcrop.org. Workhorses vs. RacehorsesCorn hybrids are often classified as “workhorses” or “racehorses.” Hybrids that produce above-average yield under good conditions but below average under poor conditions are considered racehorses, while those that have relatively consistent yields in both low- and high-yielding conditions are considered workhorses. Most hybrids that are considered to be variable performers (racehorses) have specific defects that cause them to yield lower than average when exposed to certain conditions. Growers can avoid some of the risk associated with hybrid selection by taking time to find out as much as possible about a hybrid’s past performance. Select hybrids that complement each other because they have different specific weaknesses. For example, when selecting two full-season hybrids with high yield potential for earliest planting, ensure that they don’t both score low for stalk strength. | Top of Page | StandabilityWhile selecting hybrids that have suitable maturity ratings and outstanding yield potential, evaluate hybrid selections for standability. This trait is particularly important where significant field drying is expected. If drying facilities are available on the farm and harvesting at relatively high moisture levels (>26%) is an option, standability may be less critical. Traits associated with improved hybrid standability include resistance to stalk rot and leaf blights, genetic stalk strength (a thick stalk rind), short plant height, lower ear placement and high late-season plant health. One of the most significant advancements in improved standability has been the introduction of Bt hybrids that are resistant to European corn borer. On a provincial average, Bt hybrids have generally resulted in enough yield increase over their non-Bt counterparts to pay for the additional cost of the Bt seed. Corn grown in areas of the province where corn borer pressure is traditionally high and in situations where corn is being planted earlier or later than the majority of the surrounding corn often benefits significantly from having the Bt gene. For further information on European corn borer management using Bt hybrids, refer to the section European Corn Borer. Harvest Moistures and Drying CostsHybrid selection may also be influenced by desired harvest moistures. In situations where corn is stored as high moisture grain (e.g., 28%), growers have more opportunity to maximize returns by growing full season, high-yielding hybrids. Where corn is dried for storage, growers should evaluate the impact that high harvest moistures may have on net returns. For example, any potential gains in net returns from a hybrid that yields 0.31 t/ha (5 bu/ac) greater than another may be eliminated by the increased drying charges. Selecting Hybrids for SilageWhen choosing hybrids specifically for whole-plant silage, a yield advantage can usually be obtained by selecting hybrids rated 100 to 200 heat units higher than those selected for grain. Hybrids should be selected for high silage yields with improved digestible energy. Silage-only and dual-purpose corn hybrids are marketed. Dual-purpose hybrids may provide some flexibility where grain harvest needs to be an option, such as when the silo is full. Without sufficient independent data, it is very difficult to compare and select corn silage hybrids between companies. Choose hybrids from the top of a seed company’s research for their hybrids-based ratings for silage yield, whole plant digestibility, fibre and starch digestibility. Various models are used to compare the economic value of corn silage hybrids. The University of Wisconsin has developed “Milk Per Acre” and “Milk Per Ton” calculations using their Milk 2000 program to combine the traits of silage yield, digestibilities, fibre, starch, crude protein and intake potential into a single measure. Milk per ton measures quality, while milk per acre combines yield and quality. | Top of Page | Switching to Shorter Season HybridsField conditions may delay planting and warrant consideration of switching to less than full-season hybrids. Factors to consider in this decision include yield potential of shorter season hybrids, test weight concerns, drying costs and late-season harvesting capabilities. Grain corn obtains 90% of its total grain weight by one-half milk line, a maturity stage that even late-planted, full-season hybrids reach in most years. Switching to shorter-season hybrids may be a reasonable alternative from a grain yield perspective if earlier hybrids can produce within 10% of the full-season hybrid’s yield. Generally, this is a more favourable proposition when growing 3,000 CHU hybrids as the full-season selections, which allows for switching to hybrids that are 100-150 heat units less without sacrificing excessive yield. If, on the other hand, the full season hybrids are in the 2,650-CHU range, the odds of dropping to a hybrid 100 heat units less without giving up more than 10% yield are poor. Test Weight ConcernsLower test weights often result if end-of-season frosts occur before late-planted corn has reached maturity (black layer). Consider test weight potential when selecting hybrids for planting in a late spring. Potential dockage from delivering lower bushel weight corn to an elevator or end user is shown in Table 3-10, Grain Corn Test Weights and Potential Dockage. Farming operations that handle and feed all of their own corn may be unaffected by test weight concerns and may choose to remain with full-season hybrids longer into the planting season. Experience and research from 1992 and 2000 indicated there was little or no correlation between test weight and livestock feed value. Producers who deliver all their corn to elevators or processors may want to switch to earlier hybrids to increase the potential for suitable test weights at harvest. Producers in shorter-season areas who fear significant yield losses by switching to earlier-maturing hybrids may consider staying with full-season hybrids but switching to hybrids that have higher test weight scores. 1Based on 2001 market. Potential dockage may vary considerably depending on year and location. Drying CostsFull-season hybrids and/or late plantings predispose the grower to higher drying costs at harvest. Any potential yield advantage that could be obtained from staying with later-maturing hybrids must be weighed against additional drying costs. Research conducted at Michigan State University in the 1990s is outlined in Table 3-11. The Effect of Growing Early, Mid- and Late-Maturing Hybrids on Yield, Harvest Moisture and Net Returns Across Three Zones in Michigan. Yield, harvest moisture and net returns after drying were evaluated by varying the yield, harvest moisture and net returns after drying, for hybrids of different maturity across several zones within the state. Results confirm that although later-maturing hybrids consistently outyielded earlier hybrids, drying costs generally offset any advantage in terms of net returns. When there are low-cost drying alternatives or the possibility of storing high-moisture corn on-farm, there may be less incentive to switch to shorter-season hybrids than when producers must rely on commercial drying. If the elevator charges $12.80 CDN per tonne ($0.33 CDN per bushel) to dry corn from 25% to 15.5% but charges $15.36 CDN per tonne ($0.39 CDN per bushel) to dry from 30% to 15.5% moisture, then the higher moisture corn must yield at least 0.19 t/ha (3 bu/ac) more to cover the extra drying costs. | Top of Page | |
