Limited research has been conducted on how drought-tolerant hybrids respond to plant population and planting date, especially in the Eastern Corn Belt (Roth et al., 2013). These hybrids may be able to maximize yield at higher plant populations if their stress tolerance is improved, possibly due to traits like smaller growth habit (Poorter and Garnier, 2007) and a shorter anthesis-silking interval (Lindsey, 2015), both of which have been associated with drought tolerance. The interval is the difference in days between anthesis (also knowns as tassel emergence or pollen shed) and silking (or emergence of silk from the ear). Heat and moisture stress is typical during August in Ohio, which could delay both tassel and silk emergence and decrease pollination and yield (Cicchino et al., 2010; Edreira et al., 2011). Drought-tolerant hybrids may produce greater yield than their conventional counterparts when planting is delayed because of improved flowering and grain fill under moisture stress (Butzen et al., 2009).
Drought-Tolerant Hybrid Response to Plant Population and Planting Date
As described in Drought-Tolerant Corn Hybrids: A Risk Management Tool for Ohio? Part 1, multiple field studies were conducted in Ohio from 2012–2014 at the Northwest Agricultural Research Station in Hoytville (NWARS), the Western Agricultural Research Station (WARS), and the Ohio Agricultural Research and Development Center in Wooster (WST) on soil textures that included silty clay loam, clay loam and silt loam. Weather each year was variable with drought conditions prevalent in 2012, average temperatures and precipitation in 2013 and variable conditions in 2014 that included multiple combinations of cool, hot, wet and dry periods. Drought-tolerant hybrids were compared to conventional hybrids of similar relative maturity at multiple populations (18,000–50,000 plants/A) and planting dates (May or June). Commercially available Optimum AQUAmax hybrids from DuPont Pioneer (ranging from 101-d to 114-d comparative relative maturity, or CRM) were used for both plant date and population evaluations, and Agrisure Artesian hybrids from Syngenta (ranging from 99-d to 112-d relative maturity) were used exclusively in plant-date evaluations in 2013 at NWARS and WARS. This fact sheet presents a summary of data across years and locations, but regionally specific results for NWARS and WARS can be found in supplemental sections at the end of this fact sheet (S1: NWARS; S2: WARS).
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| Figure 1A. The difference in days between tassel and silk emergence for AQUAmax drought-tolerant hybrids and their conventional counterparts at five populations when planted in May. A negative value indicates silk emergence occurred before tassel emergence. | Figure 1B. The difference in days between tassel and silk emergence for AQUAmax drought-tolerant hybrids and their conventional counterparts at five populations when planted in June. A negative value indicates silk emergence occurred before tassel emergence. |
In the field studies that evaluated population response, both conventional and drought-tolerant hybrids exhibited a similar flowering response to increasing population (Figures 1A and 1B). The anthesis-silking interval lengthened as population increased, but overall the drought-tolerant hybrids had a shorter interval compared to the conventional hybrids regardless of planting date. The plant population needed to maximize grain yield, also known as the agronomic optimum plant population (AOPP), was lower for the drought-tolerant hybrids compared to the conventional hybrids (Table 1). Both the drought-tolerant and conventional hybrids had similar yield at the AOPP within each planting date.
When examining only planting date effects, conventional hybrids produced greater yield than their AQUAmax or Artesian counterparts when planted in May (Table 1). However, the yield was similar for both hybrid types when planting was delayed until June. The yield decrease associated with delayed planting was greater for the conventional hybrids, mainly due to their 3 bu/A greater yield when planted in May.
In most cases, the population needed to maximize yield is not necessarily the population that will maximize profits. Optimizing population to maximize profit means both the cost of seed as well as the projected grain price at the end of the season should be included to determine the economic optimum plant population (EOPP). The EOPP will often be lower than the AOPP, but it will help to maximize profit per acre. The economic analysis using the data from Table 1 is provided in Table 2, with a range of grain prices and seed costs. In general, considering the economics reduced yield by 0.2–0.3 percent while decreasing seeding rate by 1,000–3,000 plants/A (3–9 percent) across all locations. The optimum populations observed in these trials are greater than are typically recommended, and may have been due to the growing conditions in 2013 and 2014. While the May-planted hybrids in 2012 experienced extreme heat and moisture stress during June and July, both 2013 and 2014 were record-breaking years for corn production in Ohio. This may have resulted in optimal populations above those previously documented.
| Table 1. Population needed to maximize grain yield (also known as the agronomic optimum plant population or AOPP), and yield at that population for each hybrid type (AQUAmax hybrids only). The last column (Yield Across Populations) contains data for both AQUAmax and Artesian hybrids, and letters denote the means within the column are significantly different. | ||||
| Plant Date | Hybrid Type | AOPP | Yield at AOPP | Yield Across Populations |
| Plants/A | ----------- bu/A ----------- | |||
| May | Drought-Tolerant | 37,928 | 199.9 | 200.0b |
| Conventional | 39,507 | 199.9 | 203.1a | |
| June | Drought-Tolerant | 38,111 | 180.8 | 177.9c |
| Conventional | 46,899 | 176.4 | 176.3c | |
| Table 2. Plant populations that maximize economic return to seed relative to market grain price per bushel and seed cost per 80,000 kernels based on the yield response of May-planted drought-tolerant (DT) and conventional (Con) hybrids across 17 trials (AQUAmax hybrids only). | ||||||||||||||
| Seed Cost | Grain Price ($/bu) | |||||||||||||
| $3.00 | $3.50 | $4.00 | $4.50 | $5.00 | $5.50 | $6.00 | ||||||||
| DT | Con | DT | Con | DT | Con | DT | Con | DT | Con | DT | Con | DT | Con | |
| $275 | 36,021 | 36,974 | 36,293 | 37,336 | 36,498 | 37,607 | 36,656 | 37,818 | 36,784 | 37,988 | 36,888 | 38,126 | 36,974 | 38,241 |
| $300 | 35,848 | 36,744 | 36,145 | 37,139 | 36,367 | 37,435 | 36,541 | 37,665 | 36,680 | 37,849 | 36,793 | 38,000 | 36,888 | 38,126 |
| $325 | 35,674 | 36,513 | 35,996 | 36,941 | 36,238 | 37,262 | 36,425 | 37,511 | 36,576 | 37,711 | 36,698 | 37,874 | 36,801 | 38,010 |
| $350 | 35,501 | 36,283 | 35,848 | 36,744 | 36,108 | 37,089 | 36,310 | 37,358 | 36,472 | 37,573 | 36,604 | 37,749 | 36,714 | 37,895 |
| $375 | 35,328 | 36,053 | 35,699 | 36,546 | 35,978 | 36,916 | 36,194 | 37,204 | 36,368 | 37,435 | 36,509 | 37,623 | 36,628 | 37,780 |
| $400 | 35,154 | 35,822 | 35,550 | 36,349 | 35,848 | 36,744 | 36,079 | 37,051 | 36,264 | 37,296 | 36,415 | 37,497 | 36,541 | 37,665 |
Conclusions
When averaged across populations, May-planted drought-tolerant hybrids were at a slight yield disadvantage compared to conventional hybrids. However, the drought-tolerant hybrids produced equivalent or greater grain yield than the conventional hybrids when planted at the optimum population in May. The optimal population to maximize yield or profit was also lower for the drought-tolerant hybrids as compared to the conventional hybrids, except at the NWARS location (which was the only site with yield below the critical level identified in Part 1 of 185 bu/A). The yield was similar regardless of hybrid type when planting was delayed until June, but the decrease in yield was slightly less for the drought-tolerant hybrids (22 bu/A decrease versus 27 bu/A decrease for conventional hybrids). The optimum population was lower for drought-tolerant hybrids than conventional hybrids in the higher yielding environments from these studies. However, in more moderate or low-yielding environments, the optimum population of drought-tolerant hybrids was greater than conventional hybrids. Because the optimum population differed slightly based on yield potential, considerations of field history may help optimize plant population of drought-tolerant hybrids.
References
Butzen, S., P. Carter, M. Jeschke, G. Luce, J. Mathesius, and B. Anderson. “Corn: Production Practices.” In Agronomy Sciences Research Summary, 3–19. Johnston, IA: Pioneer Hi-Bred, International, 2009.
Cicchino, M., J.I. Rattalino, and M.E. Otegui. “Heat Stress During Late Vegetation Growth of Maize: Effects on Phenology and Assessment of Optimum Temperature.” Crop Sci. 50 (2010): 1431–1437.
Edreira, J.I.R., E.B. Carpici, D. Sammarro, and M.E. Otegui. “Heat Stress Effects Around Flowering on Kernel Set of Temperate and Tropical Maize Hybrids.” Field Crops Res. 123 (2011): 62–73.
Lindsey, A.J. Agronomic and Physiological Responses of Modern Drought-Tolerant Maize (Zea Mays L.) Hybrids to Agronomic Production Practices. Dissertation. Columbus, OH: The Ohio State University, 2015.
Poorter, H., and E. Garnier. “Ecological Significance of Inherent Variation in Relative Growth Rate and Its Components.” In F.I. Pugnaire and F. Valladares, editors, Functional Plant Ecology, 67–100. Boca Raton, FL: CRC Press, 2007.
Roth, J.A., I.A. Ciampitti, and T.J. Vyn. “Physiological Evaluations of Recent Drought-Tolerant Maize Hybrids at Varying Stress Levels.” Agron. J. 105 (2013): 1129–1141.
S1: NWARS
At NWARS when planted in May, the agronomic optimum population for the AQUAmax hybrids was approximately 1,000 plants/A greater than the conventional hybrids, and resulted in a 2 bu/A yield advantage (S1 Table 1). When planting was delayed until June, there was a flat response to increasing population. Across populations, the Artesian and AQUAmax hybrids had similar yields to their conventional counterparts regardless of plant date. When considering the economic optimum plant population, the drought-tolerant hybrids consistently had an optimal population 900–1,000 plants/A greater than the conventional hybrids (S1 Table 2). This was the only site where the drought-tolerant hybrids exhibited a greater optimum population than the conventional hybrids, but it was also the only site with yield at or below the critical yield level identified in Part 1 (185 bu/A).
S2: WARS
At WARS when planted in May, the agronomic optimum population for the AQUAmax hybrids was 3,000 plants/A less, and grain yield was 2 bu/A less compared to the conventional hybrids (S2 Table 1). When delayed planting until June, the optimum population was 2,500 plants/A less for the drought-tolerant hybrids, but the maximum yield was 6 bu/A greater than the conventional hybrids. However, the conventional hybrids produced greater yield than the Artesian and AQUAmax hybrids when planted in May and similar yields when planted in June when averaged across populations. When considering the economic optimum, the drought-tolerant hybrids produced the greatest return when planted at populations 2,000 plants/A lower than the conventional hybrids (S2 Table 2). These results indicate that yield at the optimum population for the drought-tolerant hybrids is similar to that for the conventional hybrids in this high-yielding environment, but was less when averaged across populations when planted in May. Therefore, it is critical to plant at the optimum population to maximize the productivity and economic return of drought-tolerant hybrids at this location.
| S1 Table 1. Population needed at NWARS to maximize grain yield (also known as the agronomic optimum plant population or AOPP), and yield at that population for each hybrid type (AQUAmax hybrids only). The last column (Yield Across Populations) contains data for both AQUAmax and Artesian hybrids, and letters denote the means within the column are significantly different. The asterisk denotes the reported AOPP was not statistically significant due to a flat yield response to increasing plant population. | ||||
| Plant Date | Hybrid Type | AOPP | Yield at AOPP | Yield Across Populations |
| Plants/A | ----------- bu/A ----------- | |||
| May | Drought-Tolerant | 35,547 | 182.7 | 188.5a |
| Conventional | 34,885 | 180.5 | 186.1a | |
| June | Drought-Tolerant | 37,691* | 174.1 | 184.2a |
| Conventional | 33,915* | 165.3 | 181.8a | |
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S1 Table 2. Plant populations that maximize economic return to seed relative to market grain price per bushel and seed cost per 80,000 kernels based on the yield response of May-planted drought-tolerant (DT) and conventional (Con) hybrids across six trials at NWARS (AQUAmax hybrids only). |
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| Seed Cost | Grain Price ($/bu) | |||||||||||||
| $3.00 | $3.50 | $4.00 | $4.50 | $5.00 | $5.50 | $6.00 | ||||||||
| DT | Con | DT | Con | DT | Con | DT | Con | DT | Con | DT | Con | DT | Con | |
| $275 | 33,523 | 32,645 | 33,812 | 32,965 | 34,029 | 33,205 | 34,197 | 33,392 | 34,333 | 33,541 | 34,443 | 33,663 | 34,535 | 33,765 |
| $300 | 33,339 | 32,442 | 33,655 | 32,791 | 33,891 | 33,053 | 34,075 | 33,256 | 34,222 | 33,419 | 34,343 | 33,552 | 34,443 | 33,663 |
| $325 | 33,155 | 32,238 | 33,497 | 32,616 | 33,753 | 32,900 | 33,952 | 33,120 | 34,112 | 33,297 | 34,242 | 33,441 | 34,351 | 33,562 |
| $350 | 32,971 | 32,034 | 33,339 | 32,442 | 33,615 | 32,747 | 33,830 | 32,985 | 34,001 | 33,175 | 34,142 | 33,330 | 34,259 | 33,460 |
| $375 | 32,787 | 31,831 | 33,182 | 32,267 | 33,477 | 32,594 | 33,707 | 32,849 | 33,891 | 33,053 | 34,042 | 33,219 | 34,167 | 33,358 |
| $400 | 32,603 | 31,627 | 33,024 | 32,093 | 33,339 | 32,442 | 33,585 | 32,713 | 33,781 | 32,930 | 33,941 | 33,108 | 34,075 | 33,256 |
| S2 Table 1. Population needed at WARS to maximize grain yield (also known as the agronomic optimum plant population or AOPP), and yield at that population for each hybrid type (AQUAmax hybrids only). The last column (Yield Across Populations) contains data for both AQUAmax and Artesian hybrids, and letters denote the means within the column are significantly different. | ||||
| Plant Date | Hybrid Type | AOPP | Yield at AOPP | Yield Across Populations |
| Plants/A | ----------- bu/A ----------- | |||
| May | Drought-Tolerant | 39,563 | 218.4 | 204.8b |
| Conventional | 42,411 | 219.9 | 212.4a | |
| June | Drought-Tolerant | 38,318 | 195.9 | 171.9c |
| Conventional | 40,813 | 190.3 | 169.7c | |
|
S2 Table 2. Plant populations that maximize economic return to seed relative to market grain price per bushel and seed cost per 80,000 kernels based on the yield response of May-planted drought-tolerant (DT) and conventional (Con) hybrids across eight trials at WARS (AQUAmax hybrids only). |
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| Seed Cost | Grain Price ($/bu) | |||||||||||||
| $3.00 | $3.50 | $4.00 | $4.50 | $5.00 | $5.50 | $6.00 | ||||||||
| DT | Con | DT | Con | DT | Con | DT | Con | DT | Con | DT | Con | DT | Con | |
| $275 | 37,837 | 39,919 | 38,084 | 40,275 | 38,268 | 40,542 | 38,412 | 40,750 | 38,527 | 40,916 | 38,621 | 41,052 | 38,700 | 41,165 |
| $300 | 37,680 | 39,692 | 37,949 | 40,081 | 38,151 | 40,372 | 38,308 | 40,599 | 38,433 | 40,780 | 38,536 | 40,928 | 38,621 | 41,052 |
| $325 | 37,523 | 39,466 | 37,815 | 39,886 | 38,033 | 40,202 | 38,203 | 40,448 | 38,339 | 40,644 | 38,450 | 40,805 | 38,543 | 40,939 |
| $350 | 37,366 | 39,239 | 37,680 | 39,692 | 37,916 | 40,032 | 38,099 | 40,296 | 38,245 | 40,508 | 38,365 | 40,681 | 38,465 | 40,825 |
| $375 | 37,210 | 39,012 | 37,546 | 39,498 | 37,798 | 39,862 | 37,994 | 40,145 | 38,151 | 40,372 | 38,279 | 40,557 | 38,386 | 40,712 |
| $400 | 37,053 | 38,786 | 37,411 | 39,304 | 37,680 | 39,692 | 37,889 | 39,994 | 38,057 | 40,236 | 38,194 | 40,434 | 38,308 | 40,599 |