In the last few 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 the last growing season, Monsanto 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% yield increase over “competitor hybrids” in non-limiting and water-limiting environments, respectively.

At the present, there is limited “public” information supporting the data presented by the private seed companies; thus the K-State research data summarized in this article provides some guidance on the expected response of the DT corn hybrids when grown in diverse water regimes across the Kansas.

K-State research conducted over the last two growing seasons (2012-2013) in east central, north central, south central, and west central Kansas (6 site-years) was recently summarized. The objective is to present an overview of the DT vs. non-DT responses to management practices (i.e. 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.

Results

Our research compared DT hybrids from diverse companies with a standard non-DT counterpart of similar maturity. The tests also evaluated of 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 previous eUpdate article on corn seeding rates.

We also analyzed yields obtained 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; and blue points=on-farm plots).

Overall, the analysis found a yield benefit of 3% for DT vs. non-DT hybrids under diverse environments and stress conditions across Kansas during the 2012-2013 seasons. In absolute terms, the yield advantage of using DT hybrids was around 7 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 the yield response, positive or negative for DT vs. non-DT, was comprised between the 5% confidence interval highlighted in the below figure (Fig. 1), except at low-yielding environments (<150 bushels per acre). In low yielding-environments, there was a greater proportion of observations in which DT out-yielded non-DT corn hybrids compared to the situation in higher-yield environments (>150 bushels per acre).

Figure 1. Yield for the DT versus non-DT corn hybrids across 6 site-years for the 2012-2013 growing seasons.

DT vs. non-DT corn hybrids: Yield Environment Analysis

The analysis of information across diverse yielding environments allows us to more clearly visualize where there would be a yield advantage from planting DT hybrids. It is clear from Figure 2 that the yield advantage of the DT corn hybrids increases as the yield potential of the crop decreases. This graph shows that there is basically no yield difference 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 of100 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 other show a 60-bushel-per-acre yield advantage for DT hybrids when non-DT hybrid yields were near 70 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 model) function model fitted in the Figure 2, presented an R2 of 0.26 units, which can be interpreted to indicate that this model is accounting for 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.

DT vs. non-DT corn hybrids: Yield Winners Analysis

An extra step in our analysis can be taken by identifying the individual data points where the DT hybrids out yielded non-DT hybrids of similar maturity (DT Winners observations) and the opposite situation, in which non-DT hybrids had greater yield than the DT hybrids (non-DT Winners observations). The analysis of the data set using this approach shows a similar and consistent difference: DT hybrids out yielded non-DT hybrids when the yield for the non-DT corn material was below 171 bushels per acre (Fig. 2).

When the yield environment was higher — above the 50th percentile for both DT and non-DT Winners — yields of the two types of hybrids were comparable. But the  DT hybrids had higher yields more often than the non-DT hybrids (n=106 for DT Winners and n=68 non-DT Winners) (Table 1).

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 6 site-years for the 2012-2013 growing seasons.

Table 1. Yield Winners for DT and non-DT corn hybrids under diverse yield environments across 6 site-years for the 2012-2013 growing seasons. Yield Winners Yield environment for non-DT (bu./acre) Data Points (Percentile) Mean DT Yield (bu/acre) Mean non-DT Yield (bu/acre) DT > non-Dt <146 54 (25th) 149 124 146-161 54 (50th) 169 155 161-182 52 (75th) 183 171 182-241 54 (100th) 221 210 Non-DT > DT <165 33 (25th) 143 152 165-181 34 (50th) 162 171 181-197 34 (75th) 175 187 187-255 34 (100th) 208 216   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 benefits for the DT vs. the non-DT corn genotypes. Potential interpretations offered for the yield advantage for the DT corn hybrids are related to:

• Slower vegetative growth, saving water for reproductive stages (stress avoidance)
• Greater root biomass with superior water uptake
• Differential regulation in the stomata opening, controlling water and CO2 exchange processes
• Other potential physiological modifications

Summary

General observations from this analysis employing 6 site-years across the state of Kansas and two growing seasons (2012-2013) are:

1) Performance of individual hybrids within the drought-tolerant and regular categories may vary. Some regular hybrids can perform nearly as well as the drought-tolerant hybrids even in stressful conditions, and drought-tolerant hybrids have the potential to yield with regular hybrids when water isn’t limiting.

2) The advantage of the drought-tolerant 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 drought-tolerant 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 drought-tolerant 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; thus, 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.