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SUMMARY

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eturn to table of contents INTRODUCTION Hybrid improvements in stress tolerance have led to higher populations and increased yield potential over the years. Since 1985, average corn seeding rates used by growers in the U.S. and Canada have increased by about 300 seeds/ acre per year, while U.S. average yields have increased by almost 2 bu/acre per year (Figure 1). Seeding Rate (seeds/acre) 34,000 32,000 30,000 28,000 26,000 24,000 22,000 20,000 1985 1987 1989 Seeding Rate (U.S. and Canada) U.S. Yield y = 284.23x + 22814 R 2 = 0.9949 y = 1.8346x + 105.61 R 2 = 0.6676 1991 1993 1995 1997 1999 2001 2003 2005 2007 2009 2011 2013 2015 Figure 1. Average corn seeding rates reported by growers in the U.S. and Canada (DuPont Pioneer Brand Concentration Survey, 2015) and average U.S. corn yields (USDA/NASS). Introductions of new traits and technologies as well as continual breeding improvements may change the relationship between plant density increases and yield gains. Thus, DuPont Pioneer scientists continue to evaluate corn population responses in research trials that span the Corn Belt of North America (Figure 2). 2011 2012 2013 2014 2015 Figure 2. DuPont Pioneer plant population test locations in North America, 2011-2015. 170 160 150 140 130 120 110 100 90 80 U.S. Average Yield (bu/acre) Growers can use the multi-year and multi-location results to identify the best potential planting rates specific to their hybrid, location, and management practices. CORN SEEDING RATE TRENDS Each year, Pioneer documents seeding rate trends by surveying farmers regarding the rates currently used on their farms (Figure 4). Figure 3. Pioneer ® GrowingPoint ® agronomy on-farm seeding rate trials at 1,378 locations in North America in 2015. % of N. America Corn Acres 40 35 30 25 20 15 10 5 0 2010 2011 2012 2013 2014 2015

eturn to table of contents DUPONT PIONEER PLANT POPULATION RESEARCH RESULTS Results by Field Productivity Level Grouping locations with similar yields is a useful way to analyze plant population results because it can indicate which populations are needed for the yield levels growers intend to achieve. Like previous DuPont Pioneer studies, the current data set (2009 to 2014 trials across the U.S. and Canada) shows that the plant population required to maximize yield increases as yield level increases. Interestingly, unlike many previous results generated with older hybrids, the response curves in this study were roughly linear within the range of populations and yields represented by the data (Figure 5). Grain Yield (bu/acre) 250 225 200 175 150 125 100 Economic Optimum Seeding Rate 20 25 30 35 40 Corn Seeding Rate (1,000 seeds/acre) 240 230 220 210 200 190 180 170 150 Yield Level (bu/acre) Figure 5. Corn grain yield response to seeding rate at nine yield levels, 2009-2014. Dots indicate the economic optimum seeding rate within each yield level. Economic optimum seeding rates are based on a seed cost of $3.50/1,000 seeds and corn grain price of $4.00/bu. Optimum Economic Seeding Rate As yields increase with each higher seeding rate increment, a point is reached where the yield benefit from additional seed no longer exceeds the cost of the seed. That point is the optimum economic seeding rate. By definition, it is the seeding rate that generates the most income when factoring in seed cost and grain price. The results show that the economic optimum seeding rate increased from approximately 31,000 seeds/acre at the 150 bu/acre yield level to over 39,000 seeds/acre at the 240 bu/acre yield level (Figure 5). An Iowa State University study comparing corn yield responses to plant population across soils with different corn suitability ratings found similar results (Woli et al., 2014). Results by Hybrid Maturity Population response of five comparative relative maturity (CRM) groups is shown in Figure 6. These data show a fairly similar response of hybrid maturities to plant population. However, for the earliest hybrid maturity grouping (