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. corn yields have increased by an average of 1.9 bu/acre per year.
- Winning non-irrigated yields in the NCGA National Corn Yield Contest have increased at more than twice the U.S. average rate in the last 10 years.
- 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.
NCGA National Corn Yield Contest
The NCGA National Corn Yield Contest achieved some notable milestones during the past few seasons. A new corn yield world record was set in three of the past four years: 454.98 bu/acre in 2013, 503.72 bu/acre in 2014, and 532.03 bu/acre in 2015. A total of 25 entries exceeded 400 bu/acre over the past four years. The average yields of national winners also reached record highs in both the irrigated and non-irrigated classes in 2015 and 2014, respectively (Figure 1).
Figure 1. Average corn grain yield of NCGA National Corn Yield Contest national winners in irrigated and non-irrigated classes, 2002 to 2016.
The most remarkable achievement in the National Corn Yield Contest in recent years has been the dramatic increase in top yields in the irrigated classes. The average annual yield gain in the non-irrigated classes over the last 15 years was 5.4 bu/acre/year; well above the 1.8 bu/acre/year U.S. average yield gain over the same time period. From 2002-2010, top yields in irrigated classes increased at a similar annual rate, around 5.0 bu/acre/year. However, since 2010 the average yield gain in the irrigated classes has been over 27 bu/acre/year (Figure 1).
Yields above 300 bu/acre were achieved in a total of 373 entries in 35 states across all classes from 2013 to 2016 (Table 1). Of these 373 entries 239 were in irrigated classes and 134 in non-irrigated classes. This Crop Insights summarizes basic management practices employed in NCGA National Corn Yield Contest entries that exceeded 300 bu/acre over the past four years and discusses how these practices can contribute to higher yields 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 2016 are shown in Figure 2. Pioneer® brand products were used in the majority of entries exceeding 300 bu/acre.
Table 2. 2016 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, 2013-2016.
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 2016 are shown in Figure 3. The average harvest population of irrigated entries (37,900 plants/acre) was slightly greater than that of non-irrigated entries (36,200 plants/acre) over four 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, 2013-2016.
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 four years are combined (Figure 4). 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 4. Harvest populations and corn yield of NCGA National Corn Yield Contest entries yielding between 300 and 400 bu/acre and above 400 bu/acre, 2013-2016.
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 5). 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 5. 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, 2013-2016.
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 were planted in 30-inch rows (78%) (Figure 6). Narrower row configurations (15-inch, 20-inch, or 30-inch twin) were used in 15% of entries, and wider single or twin-row configurations were used in 7% of entries.
Figure 6. Row width used in NCGA National Corn Yield Contest entries exceeding 300 bu/acre, 2013-2016.
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 not shown a consistent yield benefit to narrower rows outside of the Northern Corn Belt (Jeschke, 2013). Results from the National Corn Yield Contest demonstrate that high yields can be attained in a variety of different row configurations.
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 May 30, 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, 2013-2016.
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 (62%) 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, 2013-2016.
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.
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 these entries, most included some form of deep tillage. Deep tillage implements included rippers, chisel plows, and subsoilers. 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.
Figure 9. Tillage practices in NCGA National Corn Yield Contest entries exceeding 300 bu/acre, 2013-2016.
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 one pound of nitrogen per bushel harvested, and stover production requires a half-pound for each bushel of grain produced. This means that the total N needed for a 300 bu/acre corn crop is around 450 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.
Figure 10. Nitrogen rates (total lbs/acre N applied) of NCGA National Corn Yield Contest entries exceeding 300 bu/acre, 2013-2016. (Note that N rates above 300 lb/acre are usually appropriate only for contest plots and high-yielding irrigated fields.)
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 is able to obtain from the soil through increased mineralization of organic N and improved corn root growth.
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.
Figure 11. Nitrogen fertilizer application timing of NCGA National Corn Yield Contest entries exceeding 300 bu/acre, 2013-2016.
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.
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 0.43 lbs of P2O5 and 0.27 lbs of K20 equivalents per bushel, according to the International Plant Nutrition Institute. That means that a 300 bu/acre corn crop will remove about 129 lbs of P2O5 and 81 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 (Schulte and Heggenstaller, 2016). 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 P in the Corn Belt in 2016.
Figure 14. Percent of soil samples that fell below state optimum levels for K 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. 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.
Figure 15. Micronutrients applied in NCGA National Corn Yield Contest entries exceeding 300 bu/acre, 2013-2016.
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.
Jeschke, M. 2013. Row Width in Corn Grain Production. Crop Insights Vol. 23, no. 16. DuPont Pioneer, Johnston, IA.
Schulte, M, and A. Heggenstaller. 2016. Soil test phosphorus and potassium levels in the Corn Belt. Agronomy Research Update. DuPont Pioneer.
1 All Pioneer products are hybrids unless designated with AM1, AM, AMT, AMRW, AMX and AMXT, in which case they are brands.
Harvest image courtesy of Case IH.
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.