Capturing Dryland Corn Yield Potential with Hybrid Flex

INSIGHTS

• Hybrids differ in their ability to efficiently recover yield potential when planted at low seeding rates.

• All Golden Harvest^® hybrids tested in the trial exhibited some degree of ear flex at low seeding rates (17,000 seeds/acre).

• Hybrids varied in how they used kernel number or kernel weight to contribute to overall yield potential flex.

Introduction

Figure 1. Decreasing plant population (left to right) can affect ear flex through total kernel number and/or kernel weight.

Hybrid selection is the most important management decision farmers face each year. After yield potential, there are a plethora of factors that are weighed when making those selections. Ear flex potential is one characteristic that is, at minimum, reviewed if not selected for. Most associate the value of ear flex with an opportunity to reduce seed costs through plant population reductions.

Hybrid flex can also provide value in water limited geographies where normal precipitation totals will not support higher seeding rates. These environments rarely experience yield responses to seeding rates greater than 20,000-24,000 seeds per acre. The goal in these environments is to plant the lowest possible seeding rate needed in a normal year.

However, this defensive approach limits yield potential in years when timely rainfall events occur. Placement of a hybrid that not only provides yield stability in the dry years, but also has enough ear flex to capture upside yield potential in wet years at lower seeding rates is useful to gain additional ROI potential (Figure 1).

Trial Details

Agronomy in Action research trials were established at three locations in the western Corn Belt (Waterloo, NE, York, NE and Clay Center, KS) in 2023 with the goal of characterizing the ability of a hybrid to recover yield at low populations when water is not a limiting factor. All three sites were irrigated to emulate non-limiting environments. Golden Harvest hybrids ranging from 97- to 117-day maturity were tested. These hybrids had ear flex ratings ranging from semi-determinant to flex, with the majority (9 of 12) in the semi-flex category (Table 1). Each hybrid was planted at 17,000 and 29,000 seeds/ac in four replications at each site.

Table 1. Hybrids assessed int he trial, their respective ear flex ratings (F: flex, SD: semi-determinant, SF: semi-flex), and yield responses to population across three Agronomy in Action research trials. Asterisk indicates significant yield change.

Hybrid Yield Recovery

Yield performance of individual hybrids at 17,000 and 29,000 seeding rates are listed in Table 1. Yield recovery (YR) was then calculated from these responses (Graph 1). This is a ratio that identifies the ability of a hybrid to fulfill its yield potential relative to an optimum yield environment through overall ear flex. It is calculated through the equation:

Graph 1. Yield recovery (%) of twelve Golden Harvest hybrids in response to population reduction from 29K to 17K. Dashed vertical line represents the trial YR average. Asterisks indicate whether a hybrid's response was significantly different than the site average.

Hybrid YR ranged from 75.8 to 94.6%, with an overall average of 84.3%. Comparison of YR of each hybrid against the overall average found that four hybrids (G03B19, G06B57, G09Y24, and G10L16 brands) were statistically more efficient at recovering overall yield potential at the 29,000 seeding rate. In comparison, two hybrid brands (G14B65 and G17A81) exhibited YR ratios below the overall average.
Combining YR with overall yield responses identifies candidates that theoretically most efficiently capitalize on abundant precipitation when it occurs when planted at low populations. For example, G10L16 brand exhibited significantly greater YR and 9% greater yield at the 17,000 rate when compared with the overall average (Table 1 and Graph 1), suggesting it may be a logical choice for this type of strategy. Other hybrids (G06B57, G09B15, G09Y24, G16K01 brands) produced YR and yields at the 17,000 seeding rate similar to, if not greater than, the averages, also indicating their possible suitability.
It's important to note that this data is only comprised from one year of testing, and only serves as an indicator of hybrid flex responses under optimal weather conditions. This trial does not provide insights into how hybrids with a high yield recovery rate in non-limiting water environments might perform under drought or heat stress conditions. It does provide good insight as to how a hybrid you may currently be planting in a water limited environment may respond in years with above normal precipitation. Additional testing will be required to verify these responses and build sound recommendations.

Factors that Contributed to Ear Flex

Most associate ear flex with ear girth and length. However, there are multiple components that factor into ear flex potential: kernel number (total rows + length) and kernel weight (density + depth). To gain a better understanding of which of these factors primarily contributed to overall ear flex in relation to plant population, all hybrids at low and high seeding rates at Waterloo, NE, were subsampled and yield components (rows/ear, kernel length, total kernels/ear, and kernel weight) were measured. On average, kernel number and weight each increased 10.0 and 8.7% when seeding rate was reduced, while kernel row number remained constant (average of 15.8 rows for both seeding rates) (Table 2). When evaluating individual hybrids, only G16Q82 brand increased its number of rows when reducing seeding rate to 17,000 (16.9 vs 15.8 at 29,000). The overall lack of change to kernel row number was surprising since it is one of the initial yield components determined by the plant prior to the V6 growth stage. One possible explanation could be that the 29,000 seeding rate was not high enough to create adequate interplant competition to cause plants to reduce kernel rows.

Average ear weight increased by 19.5% with lower seeding rates resulting from both kernel number and weight changes (Table 2). However, the individual component contribution to overall ear flex varied by hybrid. Averaged across all hybrids, kernel number and weight contributed relatively similar amounts to the overall flex (52 and 48%, respectively; Graph 2). However, six hybrid brands (G06B57, G13N18, G14B65, G15J91, G16Q82, and G17A81) gained ≥ 60% of total ear flex from increased kernel number.

In comparison, the remaining hybrid brands (G97B68, G03B19, G09B15, G10L16, and G16K01) gained ≥ 58% of its ear flex from increased kernel weight. Removing G09B15 brand from the group increased the proportion to ≥ 65%. Only G09Y24 brand exhibited a 50:50 ratio of contribution between kernel number and weight.

These results indicate that hybrid genetics play an important role in determining the contribution of specific yield components on overall flex. This is further demonstrated in Figure 2, where two 116-day hybrids, G16K01 and G16Q82 brands, exhibited vastly different yield component contribution ratios. Ear flex of G16K01 brand was largely driven by kernel weight (68%) whereas G16Q82 brand was influenced more by kernel number (68%). Relationships between the ear flex yield components and several other characteristics (yield at 17,000 seeding rate, % yield recovery, relative maturity, flex rating) were also investigated, and no significant patterns were detected. It is probable that seasonal weather influences the genetic effect on some, if not all, of these ear flex yield components. Therefore, quantifying that interaction would require multiple years of the trial.

Table 2. Response of several ear flex yield components of twelve Golden Harvest hybrids to reducing seeding rate from 29K to 17K at waterloo, NE, 2023. Different letters indicate significant reductions (P<0.10).

Determining Overall Flex Ability of a Hybrid

One potential way of using the per plant ear weight yields obtained through the ear component analysis is to calculate an ear flex ratio (EFR) for each hybrid (Graph 3). The EFR is the individual ear weight gain from reduced seeding rates divided by the high seeding rate ear weight. This ratio indicates the amount of flex each hybrid demonstrated when planted at low populations compared to when planted within its optimum dryland population range. This ratio does not suggest a hybrid’s overall suitability or placement indicators, as neither drought tolerance nor any other agronomic characteristics are factored into it. One general takeaway from this single location analysis is that all hybrids show some degree of ear flex when seeding rate is reduced from 29,000 to 17,000. For reference, a hybrid with a fully determinate ear would have an EFR of zero. Also, one important consideration is that these ratios do not perfectly align with current Golden Harvest published ear flex ratings driven largely by phenotyping. This is likely because current commercial flex ratings are based on observations across a wide spectrum of environments and populations. The EFR’s in Graph 3 are from a single location and based on quantitative rather than qualitative data. Overall, the Golden Harvest corn portfolio exhibits solid ear flex potential at low seeding rates, as indicated by an average EFR of 0.196 (dashed line in Graph 3). Four hybrid brands, (G97B68, G09B15, G10L16, and G16Q82) did exhibit EFRs that were ≥18% greater than the overall average. Additional years and locations of testing is required to verify these responses. In the future EFRs could help with identifying hybrid suitability in environments requiring low population and when key hybrid characteristics (i.e., drought tolerance) are simultaneously considered.

Graph 2. Contribution of yield components (kernel number and kernel weight) to overall ear flex of twelve Golden Harvest hybrids. Dashed line indicates where contributions of each component would be equal.

Graph 3. Ear flex rations for twelve Golden Harvest hybrids. Dashed horizontal line indicates ratio averages across all hybrids.

Summary

The combination of understanding how hybrids flex at low populations, paired with their ability to recover overall yield potential, can help with hybrid selection. Especially when trying to identify candidates that can primarily provide yield stability under normal weather conditions yet offer yield upside when conditions are favorable.

Results from the trial also indicated that the individual contributions of grain yield components (kernel number and kernel weight) are greatly influenced by genetics. Despite this, all Golden Harvest hybrids evaluated in the trial showed some degree of flex potential at low populations, meaning that selecting for ear flex and genetic diversity can be simultaneously achieved if desired.

Figure 2. Ear comparisons of two hybrids in 2023 at 29,000 and 17,000 seeding rates where kernel number (G16Q82 brand) and kernel weight (G16K01 brand) were the primary contributor to overall ear flex.