Deriving Value from Multi-Hybrid Planting
Crop Insights written by Mark Jeschke, Ph.D., Pioneer Agronomy Manager
Crop Insights written by Mark Jeschke, Ph.D., Pioneer Agronomy Manager
Advances in farming technology over the past 20 years have provided the opportunity to fine-tune crop management by varying inputs across the landscape within a field. Precision farming pioneers long envisioned that corn hybrids could be an important input for variable management (Dudding et al., 1995), considering that extension agronomists consistently rate corn hybrid selection as one of the most important factors for maximizing yield (Coulter and Van Roekel, 2009; Elmore et al., 2006; Thomson McClure, 2014). Pioneer and university scientists began initial explorations into the potential value of variable hybrid placement across a field in the mid-1990s (Jeschke and Shanahan, 2015).
Today, the technology to vary hybrid placement is readily available, making the potential value of this technology for improving yields an important consideration. In addition to potential benefits, growers must also consider potential risks as well as the cost of deploying multi-hybrid planting. Costs include the initial investment in equipment, as well as the increased effort and complexity associated with developing multi-hybrid prescriptions and managing a greater number of seed products during planting season.
Three conditions are necessary for a multi-hybrid planting strategy to provide a yield advantage. First, there must be significant within-field variation in yield due to environmental or management factors, including landscape topography and other soil variables (i.e., the more uniform a field, the less likely that multi-hybrid planting will increase yield). Secondly, there must be a difference between hybrids in yield response to the within-field environmental variation. And finally, the within-field environmental variation must have some degree of spatial predictability so that the right hybrids can be placed in the right areas of the field.
The final condition is the most challenging of the three to meet because of the effects that weather can have in shaping the growing environment in any given season. Placing a drought-tolerant hybrid, for example, would require having a reasonably good idea at the outset of the growing season where in the field drought stress is likely to be yield limiting. In general, environments with a high degree of yield variability across the landscape where yield-limiting stress does not vary greatly year-to-year due to weather are most likely to benefit from variable hybrid placement.
The most common strategy for variable hybrid placement typically involves pairing a hybrid with high yield potential and a hybrid with lower yield potential but a higher level of tolerance to a yield-limiting stress factor expected to be present within the field. In practice, these designations are often colloquially referred to as “offensive” and “defensive” hybrids, or “race-horse” and “work-horse” hybrids. The offensive hybrid is assigned to areas of the field expected to be relatively free of a yield-limiting stress factor, where it can help maximize yield, and the defensive hybrid is placed in areas where yield-limiting stress is expected, in order to help minimize yield reduction associated with it.
This approach assumes an implicit tradeoff between yield potential and stress tolerance, which may or may not be the case depending on the individual hybrid(s). A given hybrid may be high yielding and also have a high degree of tolerance to a particular yield-limiting factor (in which case the optimal strategy would be to plant the entire field to that hybrid). In general, advancements in plant breeding have helped to reduce the prevalence of this tradeoff by developing hybrids with greater yield stability across environments. Hybrid yield stability is discussed in greater detail in a previous Crop Insights article, “Strategies and Considerations for Multi-Hybrid Planting” (Jeschke and Shanahan, 2015).
Weighing the benefits and risks of deploying a multi-hybrid strategy depends in part upon the default scenario against which it is being compared; i.e., what a grower would likely do if he/she were not varying hybrid placement.
For example, consider a field that is generally very high-yielding but has a few drought-prone spots within it. The default scenario in this case would likely be to plant a high-yield potential hybrid across the whole field with the understanding that it will perform poorly in some areas. A multi-hybrid strategy in this case would involve placing a drought-tolerant hybrid in the drought-prone spots, thereby exchanging top-end yield potential for resilience against yield loss from drought stress in those portions of the field. The greatest risk associated with deploying a multi-hybrid strategy in this scenario is if drought stress does not manifest to the extent expected, in which case top-end yield potential will have been sacrificed for no gain.
Conversely, consider a field that is mostly drought-prone but has a few consistently productive areas in it. In this case, the default scenario would likely be to plant a drought-tolerant hybrid across the whole field. The multi-hybrid strategy would provide the opportunity to capture additional value by placing a higher yield potential hybrid in the highly productive spots. In this case, the greatest risk associated with the multi-hybrid strategy would be if the spots expected to be high-yielding instead experience drought stress, in which case the attempt to achieve greater yield would actually result in lower yield than if the whole field had been planted to the drought-tolerant hybrid.
Simplified examples showing different possible yield outcomes in both of these scenarios are shown in the appendix at the end of this article.
Effects of Seasonal Variability
The greatest challenge in successfully implementing a multi-hybrid strategy is knowing which hybrid to put where. The variation in growing environments across a field can be influenced by weather conditions experienced during the season.
Since the decision of where to place a hybrid must be made at the start of the season, it requires a prediction, based on knowledge of soil characteristics and field history, of the nature and extent of yield-limiting stress likely to occur. The success or failure of a multi-hybrid strategy will depend in large part on the accuracy of this prediction.
Some of the initial studies conducted by Pioneer in the 1990s illustrated how challenging this can be (Figure 1). As an example, a field-scale split-planter study conducted in Northern Illinois showed substantial variation in relative hybrid performance across the field, indicating potential value of variable hybrid placement. When the split-planter study was repeated in the same field with the same two products two years later, the pattern of relative hybrid performance was very different. A multi-hybrid prescription based on the results of the initial study would not have been suited to the conditions experienced during the subsequent season.
A multi-hybrid strategy can potentially be used to manage any yield-limiting stress for which hybrids vary in their response. However, the environmental factor most likely to provide the basis for a successful multi-hybrid management strategy is probably soil moisture. Drought frequently causes substantial reductions in yields, and hybrids often differ in their tolerance to drought stress in ways that are well-characterized. The terms “defensive” and “offensive” as applied to corn hybrids often function largely as a proxy for drought tolerance.
The primary challenge associated with successfully deploying a multi-hybrid strategy to manage drought stress is the fact that drought stress can vary greatly in severity and extent from year to year, making it difficult to satisfy the third criterion presented at the outset of this article – spatial predictability of stress that allows the right hybrids to be placed in the right areas of the field. Multi-hybrid planting will likely have a higher probability of success in places where drought stress is more predictable, such as marginal soils or drier areas of the Western Corn Belt, compared to more productive areas where rainfall is more abundant, common in the Central and Eastern Corn Belt. The remainder of this article will largely focus on multi-hybrid planting examples and research results dealing with managing drought stress.
Pioneer On-Farm Trials
Field-scale on-farm trials were conducted in 2015 to explore the potential value of variable hybrid placement. Trials were established in southwestern Iowa and northeastern Missouri; however, the Missouri trials were lost due to excessive rainfall and flooding during the growing season. Eight trials were successfully completed, all in southwestern Iowa. The trials were planted using a Kinze 4900 multi-hybrid planter. Field size ranged from 56 to 199 acres.
Management zones for the trial fields were delineated based on soil types. A hypothetical multi-hybrid prescription was created for each field by assigning one of the two hybrids to each management zone based on which hybrid was expected to be the higher-yielding of the two. In the actual prescription that was planted, blocks of both hybrids were placed within all soil types that had significant presence in the field; allowing the ability to compare yield of the hybrid assigned in the multi-hybrid prescription and the alternate hybrid in each zone and estimate the yield that would have been achieved with multi-hybrid planting vs. solid seeding of either hybrid across the entire field.
Two corn products were selected for each field based on local recommendations; designated as a “defensive” product and “offensive” product and assigned to low and high productivity management zones, respectively. Products designated as defensive were generally more drought-tolerant; while products designated as offensive generally had higher top-end yield potential and less drought tolerance. A total of four Pioneer® brand corn products were used across the eight trials (Table 1). Offensive and defensive designations for each trial are shown in Table 2. Note that Pioneer P1197AM™ brand corn was deployed as the offensive hybrid in some trials and as the defensive hybrid in others.
Table 1. Pioneer® brand corn products used in 2015 on-farm multi-hybrid planting trials.
Table 2. Corn product designations for each multi-hybrid planting trial location in Pioneer on-farm trials.
Pioneer On-Farm Trial Results
Results showed that, at all eight trial locations, the best outcome would have been achieved by planting one hybrid across the entire field (Table 3). In most cases this was the offensive hybrid. At five of the eight locations, the offensive hybrid was the best yielding across all management zones.
At the two locations where Pioneer® P1197AM™ brand corn was designated as the defensive hybrid, it was higher yielding than the offensive hybrid. The predicted whole-field average yield for the multi-hybrid prescription was usually intermediate between the predicted whole-field average yields for the two individual hybrids. Estimated yield for multi-hybrid planting was 10.8 bu/acre less on average than if the whole field had been planted to the higher yielding hybrid.
Table 3. Predicted whole-field average yield in Pioneer on-farm trials for both individual hybrids and the multi-hybrid prescription, and the difference between multi-hybrid and the better of the two hybrids.
At the three locations where the defensive hybrid had greater yield in portions of the field, the potential benefit of multi-hybrid planting was limited in part by imperfect hybrid placement; i.e., there was not perfect alignment between the zones where the defensive hybrid was assigned and zones where it actually performed better. Had hybrid placement been optimal in these three locations, multi-hybrid planting would have resulted in a whole field average yield between 0.6 and 2.6 bu/acre better than planting the entire field to the best of the two hybrids (Table 4). Lost yield potential due to imperfect hybrid placement at these locations ranged from 2.6 to 8.7 bu/acre.
Table 4. Potential yield advantage with multi-hybrid planting at select locations if hybrid placement had been optimal.
The outcome of the multi-hybrid trials in 2015 was largely driven by the weather conditions experienced during the growing season. Moisture was generally ample, in some cases excessive, in the study area in 2015, which minimized the number and extent of environments in which a more drought tolerant hybrid would provide a yield advantage. This is an example of the first risk/benefit scenario described at the beginning of this article in which multi-hybrid planting can have a downside risk if the stress factor that it is intended to manage is not present. Given that these trials were all conducted in one growing season under similar conditions, the results do not provide much insight on the potential value of multi-hybrid planting across a wider diversity of environments. However, they do provide a very good illustration of a set of conditions under which multi-hybrid planting is unlikely to provide value and could, in fact, carry significant downside risk.
South Dakota State University Research
Researchers at South Dakota State University conducted a four-year study from 2013 to 2016 comparing conventional and variable hybrid planting at several locations in South Dakota (Sexton et al., 2013; 2014; 2015; 2016). This study involved placing hybrids with greater tolerance to wet conditions in low landscape positions where there was likely to be excess moisture early in the season and more drought-tolerant hybrids at upper landscape positions likely to experience drought stress later in the season. Corn products suited to these environments were selected with the input of Pioneer agronomists (Table 5).
Table 5. Pioneer® brand corn products selected for upland and lowland environments in multi-hybrid research conducted by South Dakota State University.
For the first two years of the study, research locations were planted using a modified Monosem twin-row planter capable of switching between two hybrids. The latter two years of the study used a Kinze 4900 multi-hybrid planter. The plots were set up as field length strips and laid out so that each strip included both upland and lowland landscape positions.
Research trials were successfully completed at three locations in 2013, with multi-hybrid planting providing a significant yield benefit at two of the three. At one location, two of the multi-hybrid pairs (Pioneer® P0876AM™ and P1151AM™ brand corn and Pioneer® P0876AM™ and P0987AM1™ brand corn) yielded better than the best individual hybrid, producing overall average yields of 198 bu/acre and 197 bu/acre compared to 190 bu/acre with the whole field planted to Pioneer® P0876AM™ brand corn. This represents an ideal scenario for multi-hybrid planting, since it allowed yields greater than those achieved with any individual hybrid planted across the entire field. Results at this location also demonstrated the importance of optimal hybrid selection, as one of the multi-hybrid pairs (Pioneer® P0533AM1™ and P1151AM™ brand corn) was among the lowest yielding entries in the study. At the second location, the multi-hybrid entries were higher yielding on average, but the highest yielding pair of hybrids did not yield any more than the best individual hybrid. At the third location, multi-hybrid planting did not show a yield benefit.
Research trials were completed at two locations in 2014. Multi-hybrid planting with Pioneer® brand products provided a 6 bu/acre yield advantage at one location but no advantage at the other location. Multi-hybrid planting did not show a yield benefit at any of the four study locations in 2015. This outcome was attributed to the generally favorable growing conditions and lack of drought stress experienced during the 2015 season. Research was only conducted at one location in 2016 and did not show any yield benefit for multi-hybrid planting.
Results of the four-year study showed that multi-hybrid planting can be an effective tool to improve corn yield but that success is dependent upon hybrid selection and placement and the weather conditions experienced during the growing season. Results of trials conducted in 2015 mirrored those of the Pioneer trials in Iowa in which the yield-limiting stress the multi-hybrid prescription was designed to manage did not manifest. Unlike the Pioneer trials, the SDSU study showed little downside risk associated with multi-hybrid planting – it provided a yield benefit in some site years and no yield difference in the majority of site-years, but no instances where the outcome of a multi-hybrid pair was substantially worse than the better of the two hybrids. The risk associated with multi-hybrid planting is likely to be greatly dependent on the profiles of the individual hybrids – the greater the divergence between the two hybrids in top-end yield potential or tolerance to a key yield-limiting stress, the greater the potential to lose yield if conditions during the growing season do not play out as anticipated.
The yield benefit of variable hybrid placement in a field can be tested in on-farm trials in much the same manner as variable rate seeding prescriptions are often tested – by placing check blocks within management zones. In the case of a multi-hybrid prescription, a zone where Hybrid A is prescribed would contain a check block planted to Hybrid B nested within it. This allows an assessment of the yield advantage of the prescribed hybrid vs. the alternative. This is the method used to test the value of multi-hybrid planting in Pioneer on-farm trials conducted in 2015.
These yield comparisons within management zones can then be used to estimate the field-level average yield of the multi-hybrid prescription compared to one or each of the hybrids planted across the whole field. The most meaningful comparison would be to compare the multi-hybrid yield vs. the yield of the hybrid a grower would have been likely to choose to plant over the whole field. Since management zones are likely to vary in size, management zone yields should be weighted by acreage in estimating a whole-field average yield.
Split-planter trials provide an excellent means to explore the potential value of variable hybrid placement without the need for a multi-hybrid planter. Much of the initial research exploring the potential value of variable hybrid placement involved split-planter trials. Comparing performance of two hybrids across the landscape of a field can provide insight into the potential benefit of multi-hybrid planting. This information coupled with the multi-year yield history of the field can provide an idea as to how stable the differences in yield performance may be from year to year.
It is important to understand the methods used in multi-hybrid research trials and the manner in which the data are interpreted in order to draw meaningful inferences from the results. Several industry reports of multi-hybrid planting research results have focused solely on the difference in hybrid yield performance based on soil productivity level. (For example: Hybrid A outyielded hybrid B by 8 bu/acre on high productivity soils while Hybrid B outyielded Hybrid A by 5 bu/acre on low productivity soils.) This sort of information can give an idea of the yield benefit variable placement of two hybrids might potentially provide, but it does not provide a valid estimate of the actual field-scale yield benefit a grower is likely to realize from multi-hybrid planting for two major reasons. First, it fails to account for other factors such as differences in management zone size within a field, accuracy of hybrid placement, and spatial consistency in productivity levels year-over-year. Secondly, and more importantly, simply taking an average of the yield differences between two hybrids across management zones in a field effectively compares the multi-hybrid prescription and its inverse, which is not a useful comparison.
This point is illustrated using a highly-simplified example in Figure 2. In this example, the field is evenly split between soils characterized as high productivity and low productivity. The offensive hybrid yields 20 bu/acre more on the high productivity soils and the defensive hybrids yields 10 bu/acre more on low productivity soils, for an average difference of 15 bu/acre. However, the whole-field average yield with multi-hybrid planting would be 205 bu/acre compared to a whole-field average of 200 bu/acre using the better of the two hybrids, which means that the actual yield benefit of multi-hybrid planting is 5 bu/acre, not 15 bu/acre.
Figure 2. Simplified example showing whole field average yields with a single hybrid and multi-hybrid planting in a field evenly split between high and low productivity zones.
The commercial availability of equipment capable of variable hybrid placement has provided growers with a powerful new tool for managing yield-limiting stress in corn production. However, successfully deriving value from this technology is not without its challenges, and it will not necessarily provide a benefit to all operations. Research results presented in this summary represent a relatively small portion of the vast diversity of environments in which corn is grown. Continued on-farm experimentation across a wider range of environments will help direct multi-hybrid technology to the places where it will provide the greatest benefit.
In general, environments with a high degree of yield variability across the landscape where yield-limiting stress does not vary greatly year-to-year due to weather are most likely to benefit from variable hybrid placement. The potential benefit or risk associated with multi-hybrid planting will depend greatly on the profiles of the individual hybrids – the greater the divergence between the two hybrids in top-end yield potential or tolerance to a key yield-limiting stress, the greater the potential to capture additional yield, but also the greater the potential to lose yield if conditions during the growing season do not play out as anticipated.
Figure 1A: High Productivity Field
Figure 2A: Drought-Stressed Field
Figure 1B: High Productivity Field
Figure 2B: Drought-Stressed Field
Figure 1C: High Productivity Field
Figure 2C: Drought-Stressed Field
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