![]() The Ontario Corn Committee (OCC) conducts corn hybrid performance trials each year across the province. Producers must be able to sort through information from several key sources: public performance trial data, strip trial data (seed company or farm organization) and on-farm comparisons. This emphasizes the importance of obtaining reliable information on hybrid yield potential and adaptability. In any given hybrid performance trial, there may be a 1.9–2.5 t/ha (30–40 bu/acre) difference in yield between the highest- and lowest-yielding hybrids. Figure 1–1, Crop heat units (CHU-M1) available for corn production, or farm records will provide the heat units normally accumulated in a given area. Using crop heat unit ratings, hybrids can be selected to reach black layer before traditional season-ending frosts occurs. Physiological maturity (black layer) is achieved when all the kernels have reached their maximum dry matter accumulation and there is no additional moisture or nutrient transport from the plant. Hybrid selection for an individual farm should be done in consultation with seed company representatives. The following are a few key considerations intended as general guidelines for selecting hybrids. To remain competitive, producers must introduce new hybrids to their acreage on a regular basis. Yield increases of approximately 1.5% per year have been achieved. Corn hybrids with superior yield potential have been continuously introduced into the market place over the past 50 years. Hybrid selection is probably the single most important management decision in determining cropping profitability. Producers who record daily high and low temperatures can use Table 10–4, Daily crop heat unit accumulations based on maximum and minimum temperatures to calculate CHU for their own farm. At 20☌ during the day and 10☌ at night, one new leaf appears every 5–6 days. Therefore, at temperatures of 30☌ during the day and 20☌ at night, there is one new leaf every 2–3 days. It takes approximately 75–80 crop heat units to produce each corn leaf. Table 1–7, 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. Unfortunately, these systems are unique, and true mathematical conversions from one to the other are not possible. Other jurisdictions use different systems for quantifying the effect of temperature on corn development and for rating corn hybrid maturity. The CHU map for Ontario is found inįigure 1–1, Crop heat units (CHU-M1) available for corn production. The current CHU system and map (sometimes referred to as CHU-M1 because of the May 1 start date) are based on data from the 1971–2000 time period. The CHU system uses a calculation to arrive at a daily CHU total and employs the following trigger to mark the season end: when average temperature falls below 12☌, or the first occurrence of -2☌. Starting in 2009, Ontario began recording CHU on May 1, regardless of location or temperatures experienced up to that date. This system allows producers to select hybrids that have a high probability of reaching maturity before a killing frost occurs.ĬHU calculations require a start date, a formula for calculating CHU based on daily temperatures and an end date. 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. The Ontario crop heat unit system has been developed to calculate the impact of temperature on corn development. Unlike soybeans, day length has little effect on the rate at which corn develops. Corn development is driven primarily by temperature, especially during the planting-to-silking period.
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