Nitrogen (N) is typically the most yield-limiting nutrient and one of the largest input costs for corn production. DuPont Pioneer is aggressively working to develop hybrids that increase yield through improved N use efficiency. Researchers are applying transgenic, molecular and conventional breeding methods to enhance N utilization within the plant. Additionally, Pioneer continues to conduct extensive research on improved N application and management.
In multiple Midwest locations over the past 8 years, studies have been conducted to compare how cropping sequences and hybrids affect yield under a range of N fertility levels.
Previous research has shown that current hybrids seldom differ in their response to N. Recent studies supported these findings by showing that products of comparable maturity had similar yield responses over a range of N rates (Figure 1).
Figure 1. Response of Pioneer® 33D53AM-R™ (AM, RR2) and P1498AM-R™ (AM, RR2) brand corn to increasing N rates under continuous corn (CC) and soybean-corn (CS) averaged for rain-fed sites (Iowa, Indiana, Illinois) in 2012 and 2013.
Results also showed a 44% yield advantage associated with rotation. The average yield for continuous corn was 115 bu/acre while corn in rotation yielded 165 bu/acre. Reducing N rates resulted in a much more substantial yield decrease in continuous corn than in rotated corn. In fact, rotated corn with no applied N yielded more than continuous corn that was applied with 70% of the optimum N rate (Figure 2).
Figure 2. Influence of N rate on yield in continuous corn and corn-soybean rotation, averaged over 5 years (2009-2013).
The importance of N uptake prior to flowering cannot be overstated, as this N supports critical ear shoot development, kernel number and potential kernel size. However, research conducted over the last 5 years has shown that nitrogen needed for grain development originates from both remobilized N and continued N uptake from the soil; and that newer hybrids take up additional nitrogen postflowering compared to older hybrids.
A DuPont Pioneer study was conducted at Macomb, Ill., in 2012, comparing a “normal” rate of 200 lb N/acre with a "low" rate of 50 lb N/acre. Resulting yields averaged 250 bu/acre for the normal rate, and 100 bu/acre for the low N rate. In the normal N environment, 130, 170, and 301 lbs N/acre were taken up by V12, R1 and R6, respectively (Figure 3). Of the 195 lb N/acre contained in the grain at maturity, 63 lbs were sourced from remobilized N (from leaves, stalks, etc.) and 132 lbs were from N taken up postflowering (Figure 3).
In the low N environment (100 bu/acre yield level), N uptake was limited to 60 lbs/acre by R1, and only 27 lbs/acre were taken up postflowering (Figure 3). These reduced N levels simulate conditions when the pool of available N is low due to leaching, denitrification or under-application of N.
Figure 3. Seasonal N uptake (lbs N / acre) for commercial hybrids grown under normal N (top) and low N (bottom) supply near Macomb, Ill., during 2012.