Managing Corn for Greater Yield
Crop Insights written by Mark Jeschke, Ph.D., Agronomy Manager
- Improved hybrids and production practices are helping corn growers increase yields. Over the past 20 years, U.S. yields have increased by an average of 2.1 bu/acre/year.
- The NCGA National Corn Yield Contest provides a benchmark for yields that are attainable when conditions and management are optimized.
- The 2018 contest had 151 entries that exceeded 300 bu/acre; down from the record high of 224 entries set in 2017.
- Selecting the right hybrid can affect yield by over 30 bu/acre, making this decision among the most critical of all controllable factors.
- One of the most critical factors in achieving high corn yields is establishing a sufficient population density to allow a hybrid to maximize its yield potential.
- High-yielding contest plots are usually planted as early as practical for their geography. Early planting lengthens the growing season and more importantly, moves pollination earlier.
- Maintaining adequate nitrogen fertility levels throughout key corn development stages is critical in helping to achieve highest yields. Split applications can help reduce losses by supplying nitrogen when plant uptake is high.
Improvements in corn productivity that began with the introduction of hybrid corn nearly a century ago have continued through the present day. Over the last 20 years, U.S. corn yield has increased by an average of 2.1 bu/acre per year. These gains have resulted from breeding for increased yield potential, introducing transgenic traits to help protect yield, and agronomic management that has allowed yield potential to be more fully realized.
As growers strive for greater corn yields, the National Corn Growers Association (NCGA) National Corn Yield Contest provides a benchmark for yields that are attainable when environmental conditions and agronomic management are optimized. The average yields of NCGA winners are about double the average U.S. yields. This difference can be attributed to favorable environmental conditions, highly productive contest fields, and high-yield management practices used by contest winners.
Harvest photo courtesy of CNH.
2018 NCGA National Corn Yield Contest
Results of the 2018 NCGA National Corn Yield Contest represented somewhat of a regression toward the mean following the record-breaking results of 2017. The 2018 contest had the second-highest number of entries exceeding 300 bu/acre at 151, but this was down considerably from the high-water mark of 224 set in 2017 (Table 1). Most Corn Belt states saw a decline in 300 bu/acre entries; Illinois, Indiana, Iowa, Kentucky, and Missouri were all down considerably from 2017. Nebraska was an exception to this trend with a second consecutive year of remarkable yield results. This may be attributable to the fact that the high yield Nebraska entries were all irrigated; whereas the states that experienced a decline have a much higher proportion of non-irrigated entries. The Pacific Northwest also had a good year, with Washington, Oregon, and Idaho all posting record-high numbers of 300 bu/acre entries.
The top yield overall in the 2018 contest was 477.6877 bu/acre, which is especially remarkable given that it was achieved in Michigan with a relatively short CRM hybrid (Pioneer® P0574AM™ brand corn (AM, LL, RR2)) compared to previous contest winners. However, yields among all national contest winners were down in 2018. The average yield of non-irrigated class national winners was down slightly from an all-time high in 2017 (Figure 1). The average yield of irrigated class winners was down considerably compared to results from the past five years.
Table 1. Number of NCGA National Corn Yield Contest entries over 300 bu/acre by state, 2013-2018.
A noteworthy result of the 2018 yield contest was the high yields achieved with early CRM hybrids. The first time an entry exceeded 300 bu/acre with a <100 CRM hybrid was in 2016. A total of five entries with 98-99 CRM hybrids topped 300 bu/acre in 2018. Pioneer® P9840AMXT™ brand corn (AMXT, LL, RR2) and Pioneer® P9998AM™ brand corn (AM, LL, RR2) were the top performers in this CRM range, accounting for four of the five 300 bu/acre entries.
The average yields among national winners tend to be skewed by a small number of very high yields, particularly in the irrigated classes. Therefore, as a yield performance benchmark, it can be more useful to look at a larger set of contest entries. Table 2 shows the median yield of the top 100 yielding entries in the irrigated and non-irrigated classes. Median yields of top entries in both the irrigated and non-irrigated classes exceeded 300 bu/acre for the second year in a row, which is about 75% greater than the current U.S. average. Median yield of non-irrigated entries in 2018 was down from 2017, while median yield of irrigated entries stayed about the same.
Figure 1. Average corn grain yield of NCGA National Corn Yield Contest national winners in irrigated and non-irrigated classes, 2002 to 2018.
Table 2. Median yields of the top 100 irrigated and non-irrigated NCGA National Corn Yield Contest entries, and the USDA average U.S. corn yields from 2013 to 2018.
The top national yields in the NCGA contest tend to grab the headlines, but studying a larger group of high-performing entries can provide more insight on management practices that can be applied to improve yields in normal corn production. This Crop Insights summarizes basic management practices employed in NCGA National Corn Yield Contest entries that exceeded 300 bu/acre over the past five years and discusses how these practices can contribute to higher yield potential for all corn growers.
Hybrids tested against each other in a single environment (e.g., a university or seed company test plot) routinely vary in yield by at least 30 bu/acre. At contest yield levels, hybrid differences can be even higher. That is why selecting the right hybrid is likely the most important management decision of all those made by contest winners.
The yield potential of many hybrids now exceeds 300 bu/acre. Realizing this yield potential requires matching hybrid characteristics with field attributes, such as moisture supplying capacity; insect and disease spectrum and intensity; maturity zone, residue cover; and even seedbed temperature. To achieve highest possible yields, growers should select a hybrid with:
- Top-end yield potential. Examine yield data from multiple, diverse environments to identify hybrids with highest yield potential.
- Full maturity for the field. Using all of the available growing season is a good strategy for maximizing yield.
- Good emergence under stress. This helps ensure full stands and allows earlier planting, which moves pollination earlier to minimize stress during this critical period.
- Above-average drought tolerance. This will provide insurance against periods of drought that most non-irrigated fields experience.
- Resistance to local diseases. Leaf, stalk, and ear diseases disrupt normal plant function, divert plant energy, and reduce standability and yield.
- Traits that provide resistance to major insects, such as corn borer, corn rootworm, black cutworm, and western bean cutworm. Insect pests reduce yield by decreasing stands, disrupting plant functions, feeding on kernels, and increasing lodging and dropped ears.
- Good standability to minimize harvest losses.
Pioneer® brand products were used in 7 national winning entries (Table 3), as well as 189 state-level winning entries – more than any other seed brand. State-level winners included a total of 67 different Pioneer brand products from 42 different hybrid families ranging from 72 to 120 CRM (Appendix).
The brands of seed corn used in the highest yielding contest entries in 2013 through 2018 are shown in Figure 2. Pioneer brand products were used in more entries exceeding 350 bu/acre and 400 bu/acre than any other individual seed brand and more entries exceeding 300 bu/acre than all other seed brands combined.
Table 3. 2018 NCGA National Corn Yield Contest national winners using Pioneer brand products.
Figure 2. Seed brand planted in National Corn Yield Contest entries exceeding 300, 350, and 400 bu/acre, 2013-2018.
One of the most critical factors in achieving high corn yields is establishing a sufficient population density to allow a hybrid to maximize its yield potential. Historically, population density has been the main driver of yield gain in corn – improvement of corn hybrid genetics for superior stress tolerance has allowed hybrids to be planted at higher plant populations and produce greater yields.
Harvest populations in irrigated and non-irrigated national corn yield contest entries over 300 bu/acre from 2013 through 2018 are shown in Figure 3. The average harvest population of irrigated entries (37,200 plants/acre) was slightly greater than that of non-irrigated entries (36,500 plants/acre) over five years. However, yields over 300 bu/acre were achieved over a wide range of populations, from 25,000 to 55,000 plants/acre, demonstrating that exceptionally high populations are not necessarily a prerequisite for high yields. Although population density is important in establishing the yield potential of a corn crop, it is just one of many factors that determine final yield.
Figure 3. Harvest populations and corn yield of irrigated and non-irrigated NCGA National Corn Yield Contest entries exceeding 300 bu/acre, 2013-2018.
Harvest population and yield per plant data over a larger yield range (150-350 bu/acre), which encompasses most of the entries in the contest, show tremendous variation in the relative contribution of yield components to final yield (Figure 4). For example, entries yielding between 250 and 300 bu/acre ranged from harvest populations below 25,000 plants/acre with yield per plant over 0.60 lbs/plant to harvest populations over 45,000 plants/acre with plant yield less than 0.35 lbs/plant. However, average values for harvest population and yield per plant both increase for each successively higher yield range. These results suggest that greater plant density and greater yield per plant are both critical to driving higher yields.
Figure 4. Harvest population and yield per plant for NCGA National Corn Yield Contest entries between 150 and 350 bu/acre, 2013-2018. Large dots indicate average values for harvest population and yield/plant for each yield range.
Optimizing plant population is important for maximizing profitability. The Pioneer Planting Rate Estimator, available on www.pioneer.com, allows users to generate estimated economically optimum seeding rates for Pioneer® brand corn products based on data from Pioneer research and Pioneer GrowingPoint® agronomy trials.
Figure 5. Row width used in NCGA National Corn Yield Contest entries exceeding 300 bu/acre, 2013-2018.
The vast majority of corn acres in the U.S. are currently planted in 30-inch rows, accounting for over 85% of corn production. A majority of 300 bu/acre contest entries over the past five years have been planted in 30-inch rows (Figure 5). This proportion has increased in recent years, reaching a high of 90% in 2017 as wider row configurations (most commonly 36-inch or 38-inch) have declined in frequency and narrower row configurations (15-inch, 20-inch, 22-inch or 30-inch twin) have largely remained steady with a slight decline in 2017.
Row spacings narrower than the current standard of 30 inches have been a source of continuing interest as a way to achieve greater yields, particularly with continually increasing seeding rates. However, research has generally not shown a consistent yield benefit to narrower rows outside of the Northern Corn Belt (Jeschke, 2018).
High-yielding contest plots are usually planted as early as practical for their geography. Early planting lengthens the growing season and more importantly, moves pollination earlier. When silking, pollination and early ear fill are accomplished in June or early July, heat and moisture stress effects can be reduced. Planting dates for entries exceeding 300 bu/acre ranged from March 10 to June 4, although mid-April to early-May planting dates were most common for locations in the central Corn Belt (Figure 6).
Figure 6. Planting date, grouped by week, of NCGA National Corn Yield Contest entries exceeding 300 bu/acre, 2013-2018.
Rotating crops is one of the practices most often recommended to keep yields consistently high. Rotation can break damaging insect and disease cycles that lower crop yields. Including crops like soybean or alfalfa in the rotation can reduce the amount of nitrogen required in the following corn crop. A majority of the fields in the 300 bu/acre entries (67%) were planted to a crop other than corn the previous growing season (Figure 7).
The so-called “rotation effect” is a yield increase associated with crop rotation compared to continuous corn even when all limiting factors appear to have been controlled or adequately supplied in the continuous corn. This yield increase has averaged about 5 to 15 percent in research studies but has generally been less under high-yield conditions (Butzen, 2012). Rotated corn is generally better able to tolerate yield-limiting stresses than continuous corn; however, yield contest results clearly show that high yields can be achieved in continuous-corn production.
Figure 7. Previous crop in NCGA National Corn Yield Contest entries exceeding 300 bu/acre, 2013-2018.
Three of the six classes in the NCGA National Corn Yield Contest specify no-till or strip-till practices; however, nearly 60% of the contest entries over 300 bu/acre employed conventional, minimum, or mulch tillage (Figure 8). Tillage practices used in high-yield contest entries have stayed relatively consistent over the past several years.
Figure 8. Tillage practices in NCGA National Corn Yield Contest entries exceeding 300 bu/acre, 2013-2018.
Achieving highest corn yields requires an excellent soil fertility program, beginning with timely application of nitrogen (N) and soil testing to determine existing levels of phosphorous (P), potassium (K), and soil pH.
Corn grain removes approximately 0.67 lbs of nitrogen per bushel harvested, and stover production requires about 0.45 lbs of nitrogen for each bushel of grain produced (IPNI, 2014). This means that the total N needed for a 300 bu/acre corn crop is around 336 lbs/acre. Only a portion of this amount needs to be supplied by N fertilizer; N is also supplied by the soil through mineralization of soil organic matter. On highly productive soils, N mineralization will often supply the majority of N needed by the crop. Credits can be taken for previous legume crop, manure application, and N in irrigation water. Nitrogen application rates of entries exceeding 300 bu/acre are shown in Figure 9.
The N application rates of 300 bu/acre entries varied greatly, but a majority were in the range of 200 to 300 lbs/acre. Some entries with lower N rates were supplemented with N from manure application. Total N rates in high-yielding contest entries have declined over the last several years. In 2013, 64% of entries used N rates greater than 300 lbs/acre, compared to only 32% in 2018. As corn yield increases, more N is removed from the soil; however, N application rates do not necessarily need to increase to support high yields. Climatic conditions that favor high yield will also tend to increase the amount of N a corn crop obtains from the soil through increased mineralization of organic N and improved root growth.
Figure 9. Nitrogen rates (total lbs/acre N applied) of NCGA National Corn Yield Contest entries exceeding 300 bu/acre, 2013-2018.
Figure 10. Nitrogen fertilizer application timing of NCGA National Corn Yield Contest entries exceeding 300 bu/acre, 2013-2018.
Timing of N fertilizer applications can be just as important as application rate. The less time there is between N application and crop uptake, the less likely N loss from the soil will occur and limit crop yield. Nitrogen uptake by the corn plant peaks during the rapid growth phase of vegetative development between V12 and VT (tasseling). However, the N requirement is high beginning at V6 and extending to the R5 (early dent) stage of grain development.
Timing of N fertilizer applications in 300 bu/acre entries is shown in Figure 10. Very few included fall-applied N. Many applied N before or at planting. Over 80% of 300 bu/acre entries included some form of in-season nitrogen application, either sidedressed or applied with irrigation (Figure 11). Nearly 90% included multiple applications.
Figure 11. Nitrogen management programs of NCGA National Corn Yield Contest entries exceeding 300 bu/acre that included in-season application(s) and multiple application timings, 2013-2018.
Micronutrients were applied on approximately half of the 300 bu/acre entries (Figure 12). The nutrients most commonly applied were sulfur (S) and zinc (Zn), with some entries including boron (B), magnesium (Mg), manganese (Mn), or copper (Cu).
Figure 12. Micronutrients applied in NCGA National Corn Yield Contest entries exceeding 300 bu/acre, 2013-2018.
Micronutrients are sufficient in most soils to meet crop needs. However, some sandy soils and other low organic matter soils are naturally deficient in micronutrients, and high pH soils may make some micronutrients less available and therefore, deficient (Butzen, 2010). Additionally, as yields increase, micronutrient removal increases as well, potentially causing deficiencies.
Butzen, S. 2010. Micronutrients for Crop Production. Crop Insights Vol. 20. No. 9. Pioneer, Johnston, IA.
Butzen, S. 2012. Best Management Practices for Corn-After-Corn Production. Crop Insights Vol. 22. No. 6. Pioneer, Johnston, IA.
IPNI. 2014. IPNI Estimates of Nutrient Uptake and Removal.
Jeschke, M. 2018. Row Width in Corn Grain Production. Crop Insights Vol. 28. No. 3. Pioneer. Johnston, IA.
Appendix - 2018 NCGA State Pioneer Winners
2018 NCGA National Corn Yield Contest state-level winners using Pioneer® brand products.
1All Pioneer products are hybrids unless designated with AM1, AM, AMT, AMRW, AMX, AMXT, AML, and Q in which case they are brands.
2NCGA National Corn Yield Contest Class:
A: A Non-Irrigated
B: AA Non-Irrigated
C: A No-Till/Strip-Till Non-Irrigated
D: AA No-Till/Strip-Till Non-Irrigated
E: No-Till/Strip-Till Irrigated
AM1 - Optimum® AcreMax® 1 Insect Protection System with an integrated corn rootworm refuge solution includes HXX, LL, RR2. Optimum AcreMax 1 products contain the LibertyLink® gene and can be sprayed with Liberty® herbicide. The required corn borer refuge can be planted up to half a mile away. AM - Optimum® AcreMax® Insect Protection system with YGCB, HX1, LL, RR2. Contains a single-bag integrated refuge solution for above-ground insects. In EPA-designated cotton growing counties, a 20% separate corn borer refuge must be planted with Optimum AcreMax products. AMX - Optimum® AcreMax® Xtra Insect Protection system with YGCB, HXX, LL, RR2. Contains a single-bag integrated refuge solution for above- and below-ground insects. In EPA-designated cotton growing counties, a 20% separate corn borer refuge must be planted with Optimum AcreMax Xtra products. AMXT (Optimum® AcreMax® XTreme) - Contains a single-bag integrated refuge solution for above- and below-ground insects. The major component contains the Agrisure® RW trait, the YieldGard® Corn Borer gene, and the Herculex® XTRA genes. In EPA-designated cotton growing counties, a 20% separate corn borer refuge must be planted with Optimum AcreMax XTreme products. YGCB,HX1,LL,RR2 (Optimum® Intrasect®) - Contains the YieldGard® Corn Borer gene and Herculex® I gene for resistance to corn borer. AMT - Optimum® AcreMax® TRIsect® Insect Protection System with RW,YGCB,HX1,LL,RR2. Contains a single-bag refuge solution for above and below ground insects. The major component contains the Agrisure® RW trait, the YieldGard® Corn Borer gene, and the Herculex® I genes. In EPA-designated cotton growing counties, a 20% separate corn borer refuge must be planted with Optimum AcreMax TRIsect products.
Q (Qrome®) - Contains a single-bag integrated refuge solution for above- and below-ground insects. The major component contains the Agrisure® RW trait, the YieldGard® Corn Borer gene, and the Herculex® XTRA genes. In EPA-designated cotton growing counties, a 20% separate corn borer refuge must be planted with Qrome products. Qrome® products are approved for cultivation in the U.S. and Canada. They have also received approval in a number of importing countries, most recently China. For additional information about the status of regulatory authorizations, visit http://www.biotradestatus.com/.
RW,HX1,LL,RR2 (Optimum® TRIsect®) - Contains the Herculex I gene for above-ground pests and the Agrisure® RW trait for resistance to corn rootworm. AVBL,YGCB,HX1,LL,RR2 (Optimum® Leptra®) - Contains the Agrisure Viptera® trait, the YieldGard Corn Borer gene, the Herculex® I gene, the LibertyLink® gene, and the Roundup Ready® Corn 2 trait. HX1 - Contains the Herculex® I Insect Protection gene which provides protection against European corn borer, southwestern corn borer, black cutworm, fall armyworm, western bean cutworm, lesser corn stalk borer, southern corn stalk borer, and sugarcane borer; and suppresses corn earworm. HXX - Herculex® XTRA contains the Herculex I and Herculex RW genes. YGCB - The YieldGard® Corn Borer gene offers a high level of resistance to European corn borer, southwestern corn borer and southern cornstalk borer; moderate resistance to corn earworm and common stalk borer; and above average resistance to fall armyworm. LL - Contains the LibertyLink® gene for resistance to Liberty® herbicide. RR2 - Contains the Roundup Ready® Corn 2 trait that provides crop safety for over-the-top applications of labeled glyphosate herbicides when applied according to label directions. Herculex® Insect Protection technology by Dow AgroSciences and Pioneer Hi-Bred. Herculex® and the HX logo are registered trademarks of Dow AgroSciences LLC. YieldGard®, the YieldGard Corn Borer design and Roundup Ready® are registered trademarks used under license from Monsanto Company. Liberty®, LibertyLink® and the Water Droplet Design are registered trademarks of Bayer. Agrisure® and Agrisure Viptera® are registered trademarks of, and used under license from, a Syngenta Group Company. Agrisure® technology incorporated into these seeds is commercialized under a license from Syngenta Crop Protection AG.