Corn Hybrid Response to Plant Population: A Review for North America

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Objectives

A meta-database (124,374 observations) of yield and plant population data points was constructed from Pioneer plant population studies conducted from 2000 through 2014 in 22 U.S. states and 2 Canadian provinces.
This database was synthesized and analyzed as a part of the Pioneer Crop Management Research Awards (CMRA) Program with Dr. Ignacio Ciampitti at Kansas State University.
The main objectives of this review study were to investigate corn hybrid response to plant population across North America and identify typical response models under different yield environments, ranging from less than 100 bu/acre up to nearly 300 bu/acre.

Study Description

Pioneer corn plant population research trials were conducted from 2000 through 2014 across corn-producing areas of North America (22 U.S. States and 3 Canadian provinces) (Figure 1).
The trials were conducted in a randomized complete block design with a split-plot arrangement with two to three replications at each site.
Plant population tested across all sites ranged from less than 20,000 to more than 40,000 plants/acre.
Between 30 and 50 current commercial hybrids were tested each year.
Not all hybrids were included at each location and not all locations were included every year.

Map listing locations of plant population studies conducted by Pioneer from 2000 to 2014. — **Figure 1.** Locations of plant population studies conducted by Pioneer from 2000 to 2014. Not all locations were included every year.

Photo showing Western bean cutworm adult feeding on corn cob. — **Figure 2.** A Pioneer plant population research experiment in 2012. A low population plot is visible in the foreground.

Results

In general, corn hybrid response to plant population followed a quadratic response model in which yield increased with greater plant population up to an optimum point, beyond which yield declined.
A strong interaction between hybrid and environment (soil and weather) was observed.
Maximum attainable yield was impacted by latitude:
- Overall maximum yield was approximately 200 bu/acre for 30-35º N latitude compared to 150 bu/acre for 45-50º N latitude.
- Nonetheless, corn hybrid response to plant population was very similar with optimal plant population ranging from 34,000 to 38,000 plants/acre.
Corn yield was generally lower and optimum population was greater with hybrids of shorter comparative relative maturity (CRM).
- Long (106-115 CRM) and very long (>115 CRM) maturity hybrids generally reached their maximum yield within a very narrow plant population range of 34,000 to 35,000 plants/acre.
- On the opposite CRM range, very early to medium (< 78 CRM to 105 CRM) maturity hybrids typically achieved maximum yield at plant populations ranging from 36,000 to 39,000 plants/acre.
Averaged over all hybrids, yield response to plant population depended on the yield environment (Figure 3).
For low yielding environments (below 100 bu/acre), a maximum yield of 93 bu/acre was attained at a plant population level of 24,000 plants/acre.
- As plant population increased in yield environments below 100 bu/acre, yield response was flat to slightly negative.
- For the lowest yield environments, productivity was limited primarily by water supply.
For medium yield environments (100 to 150 bu/acre), a maximum yield of about 135 bu/acre was attained at a plant population level of 24,000 plants/acre.
- Further increases in plant population produced a flat to slightly declining yield response (Figure 3).
For high yield environments (150 to 200 bu/acre), yield increased sharply for plant density increases from 18,000 to 30,000 plants/acre, followed by a relatively lower yield gain as plant population surpassed 30,000 plants/acre.
- Maximum yield (~170 bu/acre) was achieved at a plant population of 40,000 plants/acre; however, yield response was relatively flat at plant populations above 30,000 plants/acre (Figure 3).
For very high yield environments (above 200 bu/acre), yield response to plant population continued to increase even at 40,000 plants/acre (Figure 3).
It is important to note that plant population for highest possible yield does not necessarily coincide with the “economic” optimum plant population.
- Corn hybrid agronomic factors such as lodging and seed costs should also be taken into account when deciding the seeding rate for corn.
- In addition, as previously mentioned, optimum seeding rate can vary based on hybrid maturity and production practices, such as planting date, row spacing, seedbed condition and residue cover.

Chart showing corn hybrid response to plant population under low and medium yield environments.

Chart showing corn hybrid response to plant population under high and very high yield environments. — **Figure 3.** Corn hybrid response to plant population under four yield environments, a) low yielding <100 bu/acre; b) medium yielding 100-150; c) high yielding 150-180 bu/acre; and d) very high yielding 190-210 (Assefa et al., 2016, Crop Science Journal).

When selecting a hybrid, keep in mind not only the response to seeding rate but also the degree of tolerance to drought and/or other stresses, and also consider traits such as specific herbicide tolerance, disease and insect resistance, maturity, lodging, and overall hybrid performance.
Consult your Pioneer sales representative to determine if seeding rates for specific hybrids should be at the lower or upper end of the recommended ranges for a given environment.
Producers should consider experience and performance in previous growing seasons to determine if the seeding rate previously employed in their different fields was adequate for their respective yield environments.

Conclusions

The optimal seeding rate and final plant population depends on the environment, hybrid, and cultural practices. Producers can look back at previous corn growing seasons to evaluate if the seeding rate utilized was adequate for their yield environments.
Optimal plant density to maximize yield is not the same as the economically optimal density. The Pioneer Planting Rate Estimator, available on www.pioneer.com, allows users to generate estimated economically optimum seeding rates for Pioneer^® brand corn products based on data from Pioneer research and Pioneer^® GrowingPoint^® agronomy trials.
In summary:
- Maximum attainable yield was impacted by latitude but corn hybrid response to plant population was very similar across latitudes, with optimal plant population ranging from 34,000 to 38,000 plants/acre.
- Long- and very long-maturity hybrids reached their maximum yield within a very narrow plant population range of 34,000 to 35,000 plants/acre. On the opposite end of the CRM range, very early- to medium-maturing hybrids typically reached maximum yield at plant populations between 36,000 to 39,000 plants/acre.
- Optimal plant population varies with yield environment. Low yielding environments (< 100 bu/acre) required about 20,000 plants/acre when yield limitations were caused by water supply. High yielding (>200 bu/acre) environments generally needed at least 30,000 plants/acre but yield gain was still observed for very high yielding environments even at 40,000 plants/acre.