In recent years, drought conditions have raised questions about the utilization of corn as the main crop for maximizing yield production per unit of available water in dryland environments.
Non-transgenic (conventionally bred, Pioneer and Syngenta) corn hybrids, or so-called “drought-tolerant” (DT) hybrids, came to the market with the expectation of increasing corn production in water-limited regions. In recent growing seasons, Monsanto also released its new biotech transgenic-DT hybrid.
Overall, the information from seed companies indicates that DT hybrids could provide from 2 to more than 15 percent yield increase over “competitor hybrids” in non-limiting and water-limiting environments, respectively.
K-State research conducted over the 2012-2014 growing seasons across the state has recently been summarized. The objective of this research summary is to present an overview of the DT vs. non-DT responses to management practices such as plant population and irrigation.
The information below is intended to provide some guidance to farmers, consultants, and agronomists in making the right decision for selecting corn hybrids. In addition, we hope to develop a better understanding of the kinds of environments in which DT hybrids could be most likely to result in a yield benefit. These hybrids are generally targeted for water-limited environments in the Western Great Plains.
Our research compared DT hybrids from diverse companies with a standard non-DT counterpart of similar maturity. The tests also evaluated the yield response to varying plant population and irrigation levels.
At the plant scale, our analysis did not reveal any change in the plant response to plant population between DT and non-DT hybrids. This indicates no need to change plant population when using DT hybrids. This conclusion was briefly introduced in a last year’s eUpdate article on corn seeding rates (Agronomy eUpdate 445, March 14, 2014).
We also analyzed yields at the plot level for DT vs. comparable DT hybrids with similar maturity. The information presented in the figure below (Fig. 1) depicts the association of the yields for the DT vs. non-DT corn hybrids: Red points = research plots (2012-2013); blue points = on-farm plots; green points = 2014 growing season plots.
Overall, the analysis found a yield benefit of 3 percent for DT vs. non-DT hybrids under diverse environments and stress conditions across Kansas during the 2012-2014 seasons. In absolute terms, the yield advantage of using DT hybrids was around 5 bushels per acre compared to the non-DT material. Similar yield trends were observed in research plots and on-farm demonstration plots. A great proportion of DT and non-DT yields were similar -- within a 5% confidence interval as highlighted in Figure 1 -- except in low-yielding and high-yielding environments. In low yielding-environments, DT out-yielded non-DT corn hybrids more often compared to the situation in higher-yield environments.
Figure 1. Yield for the DT versus non-DT corn hybrids across several site-years for the 2012-2014 growing seasons.
DT vs. non-DT corn hybrids: Yield Environment Analysis
The analysis of information across diverse yielding environments allows us to more clearly understand where there would be a yield advantage from planting DT hybrids. It is clear from Figure 2 that the yield advantage of DT corn hybrids increases as the yield potential of the crop decreases. This graph shows that there is basically no yield difference between DT and non-DT hybrids when yields are around 170 bushels per acre or greater. The yield advantage for DT hybrids gradually increases as the yield of the regular hybrids decreases from 170 bushels per acre.
It is important to note however, that these are generalized relationships, and that there are varied responses at each yield level. Some individual points show no difference between DT vs. non-DT hybrids at yields around 100 bushels per acre. Other points show a 30-bushel-per-acre yield advantage for non-DT hybrids at 160 to 170 bushels per acre, and still others show a 60-bushel-per-acre yield advantage for DT hybrids when non-DT hybrid yields were near 70 bushels per acre. On the opposite side of the yield environments, under high yield environments (>220 bushel-per-acre), individual points show a 30 to 60-bushel-per acre yield advantage for non-DT hybrids when DT hybrid yields were above 220 bushels per acre. How individual hybrids respond to a specific environment is influenced by a number of factors, including the timing and duration of the stress.
One more technical clarification is important to note. The linear response and plateau (LRP) function model fitted in Figure 2 (adjusted to the 2012-2013 data), presented an R2 of 0.26 units, which can be interpreted to indicate that this model is accounting for only slightly more than one-fourth of the total variation presented in the data. In other words, there are many management factors involved in the yield results, which makes it difficult to separate out the effect of hybrid alone.
Figure 2. Yield advantage for DT compared to non-DT corn hybrids at the same environment and population, ranging from low-yielding environments to high-yielding environments across several site-years for the 2012-2014 growing seasons.
Still, we need to be cautious using and interpreting this information. More experiments and research data need to be collected, and a deeper understanding is needed to more properly comprehend the main causes of the yield differences of DT vs. non-DT corn genotypes. Potential interpretations offered for the yield advantage for the DT corn hybrids in certain environments are:
1) Performance of individual hybrids within DT and non-DT types may vary. Some non-DT hybrids can perform nearly as well as the DT hybrids even in stressful conditions, and DT hybrids have the potential to yield with non-DT hybrids when water isn’t limiting.
2) The advantage of the DT hybrids became more evident when the water stress increased to the point of leaves rolling most days.
3) From the information at hand, it is reasonable to expect a DT hybrid to serve as a type of insurance policy to sustain yield potential under water-limited environments. It also appears that there is no yield penalty associated with DT hybrids if water-limiting conditions do not occur.
Lastly, it is critical to understand that these corn genetic materials will not produce yield if the environment is subjected to terminal drought. We cannot expect them to thrive when moisture is severely limited, especially in dryland systems. As properly and explicitly stated by all seed companies, these DT materials have demonstrated the ability maintain yields to a certain degree in water-limited situations, and those differences will likely be in the order of 5 to 15 bushels per acre (depending on the environments and crop practices), when compared with a similar maturity non-DT corn hybrid.
Ignacio Ciampitti, Crop Production and Cropping Systems Specialist
Eric Adee, Agronomist-In-Charge, Kansas River Valley and East Central Experiment Fields
Kraig Roozeboom, Cropping Systems Agronomist
Alan Schlegel, Agronomist-in-Charge, Southwest Research-Extension Center, Tribune
Gary Cramer, Agronomist-in-Charge, South Central Experiment Field
Stu Duncan, Northeast Area Crops and Soils Specialist
Doug Shoup, Southeast Area Crops and Soils Specialist