The distribution of precipitation over the growing season has been changing since 1971 for the upper midwestern United States (including Ohio), and extreme precipitation events have increased 37 percent over the last 45 years (Morton et al., 2015). Changes in precipitation distribution could increase the incidence of drought events (Kunkel et al., 1999). Drought in 2012 reduced the average corn grain yield in Ohio by 25 percent compared to 2010 and 2011, which resulted in an economic loss to farmers of more than $700 million (USDA-NASS, 2015).
Drought tolerance can be defined as the ability of a plant to survive in stress periods with low internal water levels (Levitt, 1972). A new generation of drought-tolerant hybrids has been introduced in recent years, primarily for use in the Western Corn Belt where water deficits are more frequent than in Ohio. Grower adoption of these drought-tolerant hybrids in the Eastern Corn Belt will depend on whether a yield advantage or yield disadvantage is incurred. With improved genetic screening techniques as well as a large number of locations to screen new genetics, breeders have been able to identify many high-yielding hybrids with good yield stability across both favorable (8,725 locations) and water-limited (2,006 locations) environments (Gaffney et al., 2015). Many of these sites were concentrated in the Western Corn Belt, and there has been limited research published on these hybrids in the Eastern Corn Belt (Roth et al., 2013).
Performance of Drought-Tolerant Hybrids Compared to Conventional Hybrids
Field studies were conducted in Ohio from 2012–2014 at the Northwest Agricultural Research Station in Hoytville (NWARS), the Western Agricultural Research Station (WARS) near South Charleston, 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 (periods of cool and wet followed by hot and dry). Drought-tolerant hybrids containing native traits for tolerance were compared to conventional hybrids of similar relative maturity at multiple populations (18,000–50,000 plants/A), planting dates (May or June), and nitrogen rates (0–280 lbs N/A). Commercially available Optimum AQUAmax hybrids from DuPont Pioneer (ranging from 101-d to 114-d comparative relative maturity, or CRM) and Agrisure Artesian hybrids from Syngenta (ranging from 99-d to 112-d relative maturity) were included in the evaluations. Across these three years, 26 drought-tolerant hybrids were evaluated against 26 conventional counterparts of similar maturity (within 2-d) in 23 field experiments. Figure 2 depicts the yield level at which drought-tolerant hybrid exhibited an advantage over the conventional hybrid. The conventional hybrid yield is shown on the x-axis, and the y-axis shows the yield advantage of the drought-tolerant hybrid (calculated by subtracting the conventional hybrid yield from the drought-tolerant hybrid yield under identical management conditions).
|Figure 1. Drought-stressed corn field in Hoytville, Ohio, June 27, 2012.||Figure 2. Yield advantage of the drought-tolerant hybrids over the conventional hybrids. The line crosses the x-axis when the conventional hybrid yield is 185 bu/A.|
|Figure 3A. Frequency of a yield advantage from drought-tolerant hybrids when conventional hybrid yield was <185 bu/A.||Figure 3B. Frequency of a yield advantage from drought-tolerant hybrids when conventional hybrid yield was >185 bu/A.|
The drought-tolerant hybrid yield advantage was positive when the conventional hybrid yield was less than 185 bu/A, which is the point where the line crosses the x-axis. This value is approximately 10 bu/A above the state yield average for Ohio in 2013 and 2014 (USDA-NASS, 2015). In environments where the yield potential for conventional hybrids was below 185 bu/A (941 occurrences), the drought-tolerant hybrids produced greater yields 61 percent of the time (Figure 3A). When the conventional hybrids produced grain yield greater than 185 bu/A (1,194 occurrences), the drought-tolerant hybrid yield advantage was negative and produced less yield 62 percent of the time (Figure 3B). These results suggest that in moderate to lower yielding environments in Ohio (below 185 bu/A average yield), the drought-tolerant hybrids can produce greater yield than their conventional counterparts under the same management conditions, but the yield may not be greater when conventional hybrids yield more than 185 bu/A. A similar yield advantage was observed in Kansas from using drought-tolerant hybrids where the state yield average was 138 bu/A in 2013 and 2014 (USDA-NASS, 2015). The drought-tolerant hybrids exhibited a yield advantage when the conventional hybrid yield was less than 136 bu/A, but yield was similar between hybrid types when the conventional hybrid yield was greater than 136 bu/A (Ciampitti et al., 2015). In Ohio, the drought-tolerant hybrids exhibited more stable yield than the conventional hybrids in that the low yield was not as low, and the highest yield was not as high. This supports the statements presented by Cooper et al. (2014) that these drought-tolerant hybrids have been bred for improved yield stability across environments. In summary, drought-tolerant hybrids may offer a yield advantage in production environments at greater risk to water deficit with moderate- to low-yield potential.
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