Drought-Tolerant Corn Hybrids: A Risk Management Tool for Ohio? Part 2

Part 2: Plant Date and Population Response of Drought-Tolerant Hybrids
AGF-517
Agriculture and Natural Resources
Date: 
10/30/2015
A.J. Lindsey, Department of Horticulture and Crop Science
P.R. Thomison, Department of Horticulture and Crop Science

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).

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

 

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).

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).

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

 

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