Managing Corn for Greater Yield
Crop Insights by Mark Jeschke, Ph.D., DuPont Pioneer Agronomy Information 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 1.9 bu/acre/year.
- The NCGA National Corn Yield Contest provides a benchmark for yields that are attainable when conditions and management are optimized.
- The 2017 contest had 224 entries that exceeded 300 bu/acre; far more than in any previous year.
- Selecting the right hybrid can affect yield by over 30 bu/acre, making this decision among the most critical of all controllable factors.
- 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.
- Rotating crops is an important practice to help keep yields consistently high. Rotation can break damaging insect and disease cycles that reduce crop yields.
- Maintaining adequate nitrogen fertility levels throughout key corn development stages is critical in achieving 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 1.9 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.
2017 NCGA National Corn Yield Contest
The NCGA National Corn Yield Contest has achieved some notable milestones during the past few seasons, and 2017 was no exception. One of the most noteworthy aspects of the 2017 contest was that it had far more entries over 300 bu/acre than in any previous year – 224 compared to the previous high of 136 in 2014 (Table 1). Most of the surge in high-yield entries came from the central Corn Belt. Illinois, Indiana, Iowa, Kentucky, and Nebraska all had at least 2x the number of >300 bu/acre entries than in any previous year. Nebraska alone accounted for 41 of the 224 entries over 300 bu/acre. Average corn yields were high in each of these states in 2017 – all five recorded their highest or second-highest yield according to USDA – but none had a dramatic increase in average yield over previous seasons that would correspond with the dramatic increase in extremely high yields observed in the NCGA contest.
A new corn yield world record of 542.27 bu/acre was set in 2017. This is the fourth time in the last five years that a new record has been set, following records of 454.98 bu/acre in 2013, 503.72 bu/acre in 2014, and 532.03 bu/acre in 2015. Both the 2015 and 2017 record yields were set with Pioneer® P1197AM™ brand corn.
A total of 31 entries exceeded 400 bu/acre over the past four years. 2017 marked the first time a yield over 400 bu/acre was achieved outside of the Southern U.S., with the top yield of 407.22 bu/acre in the irrigated class coming from an entry in Michigan planted with Pioneer® P0574AM™ brand corn.
Table 1. Number of NCGA National Corn Yield Contest entries over 300 bu/acre by state, 2013-2017.
The average yields of national winners in the non-irrigated classes reached a record high of 347.6 bu/acre in 2017 (Figure 1). The average yield of national winners in the irrigated classes in 2017 was 463.1 bu/acre, which was second only to the record high of 484.4 bu/acre set in 2015.
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.
Figure 1. Average corn grain yield of NCGA National Corn Yield Contest national winners in irrigated and non-irrigated classes, 2002 to 2017.
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 2017.
Median yields of top entries in both the irrigated and non-irrigated classes were around 300 bu/acre, which is about 75% greater than the current U.S. average. All three metrics hit record highs in 2017.
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.
The brands of seed corn used in the highest yielding contest entries in 2013 through 2017 are shown in Figure 2. Pioneer® brand products were used in the majority of entries exceeding 300 bu/acre and a plurality of entries over 350 bu/acre and 400 bu/acre.
Table 3. 2017 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, 2013-2017.
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 2017 are shown in Figure 3. The average harvest population of irrigated entries (37,500 plants/acre) was slightly greater than that of non-irrigated entries (36,300 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, 2013-2017.
One of the most interesting aspects of the relationship between yield and plant population of high yield entries in the National Corn Yield Contest is the emergence of two distinct patterns when data from the last five years are combined. For entries between 300 and 400 bu/acre, there is no consistent relationship between harvest population and yield – populations cover a wide range, with the majority between 32,000 and 42,000 plants/acre. For entries above 400 bu/acre, however; there emerges a roughly linear relationship between population and yield, with each 5,000 plants/acre increase in population corresponding to a 30 bu/acre increase in yield (Figure 3).
When harvest population and yield per acre are used to calculate yield per plant, the resulting data show a decline in grain weight per plant as population increases, as would be expected (Figure 4). However, for exceptionally high yielding entries, the rate of this decline was not as steep. These results show that the key to success for top performing entries over the last few years has been to maintain greater yield per plant at high population densities. The fact that yields over 400 bu/acre have only been achieved under irrigation suggests that optimal water management is critical to maintaining high individual plant yield at high population density.
Figure 4. Harvest populations and yield per plant of NCGA National Corn Yield Contest entries yielding between 300 and 400 bu/acre and above 400 bu/acre, 2013-2017.
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 5). 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.
Optimizing plant population is important for maximizing profitability, particularly when commodity prices are low. The DuPont Pioneer Planting Rate Estimator, available on www.pioneer.com and as a free mobile app, 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. Harvest population and yield per plant for NCGA National Corn Yield Contest entries between 150 and 350 bu/acre, 2016-2017. Large dots indicate average values for harvest population and yield/plant for each yield range.
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 6). 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, 2013).
Figure 6. Row width used in NCGA National Corn Yield Contest entries exceeding 300 bu/acre, 2013-2017.
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 7).
Figure 7. Planting date, grouped by week, of NCGA National Corn Yield Contest entries exceeding 300 bu/acre, 2013-2017.
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 8).
Figure 8. Previous crop in NCGA National Corn Yield Contest entries exceeding 300 bu/acre, 2013-2017.
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 9. Tillage practices in NCGA National Corn Yield Contest entries exceeding 300 bu/acre, 2013-2017.
Three of the six classes in the NCGA National Corn Yield Contest specify no-till or strip-till practices; however, over 60% of the contest entries over 300 bu/acre employed conventional, minimum, or mulch tillage (Figure 9). Of the 48% of entries employing conventional tillage, most included some form of deep tillage. Deep tillage implements included rippers, chisel plows, and sub-soilers. When fields are adequately dry, deep tillage can alleviate deep compaction and break up claypans and hardpans that restrict corn root growth. Deep roots are especially important as soil moisture is depleted during mid to late summer.
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 10.
The N application rates of 300 bu/acre entries varied greatly, but a majority were in the range of 250 to 350 lbs/acre. Some entries with lower N rates were supplemented with N from manure application. 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 10. Nitrogen rates (total lbs/acre N applied) of NCGA National Corn Yield Contest entries exceeding 300 bu/acre, 2013-2017.
(Note that N rates above 300 lb/acre are usually appropriate only for contest plots and high-yielding irrigated fields.)
Figure 11. Nitrogen fertilizer application timing of NCGA National Corn Yield Contest entries exceeding 300 bu/acre, 2013-2017.
Figure 12. Nitrogen management programs of NCGA National Corn Yield Contest entries exceeding 300 bu/acre that included in-season application(s) and multiple application timings, 2013-2017.
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 11. 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 12). Nearly 90% included multiple applications.
Phosphorus and Potassium
Assuming soils are maintained at adequate levels, growers should add at least the level of P and K that will be removed by the crop. In addition, these nutrients should be available in the root zone of the developing seedling. Corn grain removes about 0.35 lbs of P2O5 and 0.25 lbs of K20 equivalents per bushel, according to the International Plant Nutrition Institute (IPNI, 2014). That means that a 300 bu/acre corn crop will remove about 105 lbs of P2O5 and 75 lbs of K20 per acre. Recent evidence suggests that P and K fertilizer rates in some areas may not be keeping pace with increasing crop yields that are accompanied by higher nutrient removal. DuPont Pioneer agronomists and Encirca certified services agents collected soil samples from 8,925 fields in 12 Corn Belt states between fall 2015 and spring 2016 (Jeschke et al., 2017). Results of this survey showed that P and K levels below state optimum levels were common across the Corn Belt (Figure 13 and Figure 14).
Figure 13. Percent of soil samples that fell below state optimum levels for phosphorus in the Corn Belt in 2016.
Figure 14. Percent of soil samples that fell below state optimum levels for potassium in the Corn Belt in 2016.
Micronutrients were applied on approximately half of the 300 bu/acre entries (Figure 15). The nutrients most commonly applied were sulfur (S) and zinc (Zn), with some entries including boron (B), magnesium (Mg), manganese (Mn), or copper (Cu). Micronutrients are sufficient in most soils to meet crop needs.
Figure 15. Micronutrients applied in NCGA National Corn Yield Contest entries exceeding 300 bu/acre, 2013-2017.
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. DuPont Pioneer, Johnston, IA.
Butzen, S. 2012. Best Management Practices for Corn-After-Corn Production. Crop Insights Vol. 22, no. 6. DuPont Pioneer, Johnston, IA.
IPNI. 2014. IPNI Estimates of Nutrient Uptake and Removal.
Jeschke, M. 2013. Row Width in Corn Grain Production. Crop Insights Vol. 23, no. 16. DuPont Pioneer, Johnston, IA.
Jeschke, M., J. Mathesius, K. Reese, B. Myers, and A. Heggenstaller. 2017. Phosphorus and Potassium Levels in the Corn Belt. Crop Insights Vol. 27. No. 5.
The foregoing is provided for informational use only. Please contact your Pioneer sales professional for information and suggestions specific to your operation. Product performance is variable and depends on many factors such as moisture and heat stress, soil type, management practices and environmental stress as well as disease and pest pressures. Individual results may vary. Encirca® services provide estimates and management suggestions based on statistical and agronomic models. Encirca services are not a substitute for sound field monitoring and management practices. Individual results may vary and are subject to a variety of factors, including weather, disease and pest pressure, soil type, and management practices.