Corn Historical Yield Trends from 1987 through 2015 for North America

Objectives

A meta-database (181,395 observations) of yield and plant population data points was constructed from Pioneer plant population studies conducted from 1987 through 2015 in 23 U.S. states and 3 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 examine yield trends across different yield environments for the 1987 to 2015 period.

Study Description

Pioneer corn plant population research trials were conducted from 1987 through 2015 across corn-producing areas of North America (23 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 five replications at each site.
Plant population tested across all sites ranged from 15,000 to close to 50,000 plants/acre. About 30 to 50 important commercially-available Pioneer^® brand hybrids were tested each year.
Not all hybrids were included at each location and not all locations were included every year.

Map showing locations of plant population studies conducted by Pioneer from 1987 to 2015. — **Figure 1.** Locations of plant population studies conducted by Pioneer from 1987 to 2015. Not all locations were included every year.

Results

Average corn yield over the duration of the study was 162 bu/acre, increasing from 135 bu/acre in 1987 to 188 bu/acre in 2015, representing an overall yield gain of 53 bu/acre.
Maximum attained yields also increased over the 1987 to 2015 period, with yields increasing from 240 bu/acre to 320 bu/acre, representing a yield gain of 60 bu/acre.

Latitude

Latitude groups were evaluated and considered as a main factor for studying corn yield trends over time.
Average corn yield was lower at higher latitudes ranges: 30º to 35º = 184 bu/acre; 35º to 40º = 172 bu/acre, 40º to 45º = 162 bu/acre, and 45º to 50º N = 142 bu/acre.
Corn yield increased across all three latitude groups included in the analysis over the 1987 to 2015 period (Figure 2)
- Corn yield gain for the 35 to 40º latitude group was 1.7 bu/acre per year.
- Corn yield gain for the 40 to 45º latitude group was 1.5 bu/acre per year.
- Corn yield gain for the 45 to 50º latitude group was 1.86 bu/acre per year.
Yield gain observed at all latitudes was a result of yield improvement across all the respective Comparative Relative Maturity (CRM) groups.

40� to 45� — **Figure 2.** Corn yield trends for the 35º to 40º, 40º to 45º, and 45º to 50º N latitude ranges for the study years from 1987 to 2015. (Assefa et al., 2017, Crop Science Journal).

Yield Environment

The meta-database was divided into four yield environments to evaluate the average yield trend for each environment over the study period: low-yielding, LY (<110 bu/acre), medium-yielding, MY (110–160 bu/acre), high-yielding, HY (160–210 bu/acre), and very high-yielding, VHY (>210 bu/acre).
Corn yield trends for each yield environment for the 1987 to 2015 period (Figure 3):
- 0.9 bu/acre per year in VHY environments
- 0.3 bu/acre per year in HY environments
- 0.15 bu/acre per year in MY environments
- no significant historical yield change in LY environments
Overall, VHY and HY environments presented a greater yield improvement over time relative to the MY and LY environments (Figure 3).
In addition to corn yield gain within yield environments, the proportion of sites falling within each yield environment category, expressed as a frequency relative to the total, was investigated for three segments of the study period: 1987-1996, 1997-2006, and 2007-2015 (Figure 4).
- The proportions of LY and MY environments decreased from the earliest decade (1987–1996) compared to the most recent historical period (2007–2015).
- The proportion of HY and VHY environments increased from the earliest to the most recent decade.
- In addition, the proportion of the LY and MY environments shrunk from ~50% to 25% for the 35 to 40º and 40 to 45º N latitude groups and from ~75% to 40% for 45 to 50º N latitude group.
- Lastly, changes over time in yield gain and the frequency of yield environments are one of the major reasons for the consistent yield gain trends recorded for the North America during the last three decades.
Over the entire study area, using data from the dominant CRM hybrids for each latitude and optimal plant population for each yield environment, an overall annual yield gain of 2.2 bu/acre per year was documented.

Chart showing proportion of corn yield environments by decade, Pioneer planting studies. — **Figure 4**. Proportion of corn yield environments by decade (1987-1996; 1997-2006; 2007-2015): low yielding (<110 bu/acre), medium yielding (110-160 bu/acre), high yielding (160-210 bu/acre), and very high yielding (>210 bu/acre) (Assefa et al., 2017, Crop Science Journal).

Conclusions

This historical corn yield study documented yield changes from 135 bu/acre in 1987 to 188 bu/acre in 2015 – an overall yield gain of 53 bu/acre.
Similarly, maximum attained yield also increased over the 1987 to 2015 period, from 240 bu/acre to 320 bu/acre, representing a yield gain of 60 bu/acre.

In Summary:

Corn yield increased across all latitudes. Yield gain was similar among latitude ranges, from 1.5 to 1.8 bu/acre per year.
Yield increase per latitude was similar across all the corn CRM hybrid groups.
Corn yield gain over the study period was greater in higher-yielding environments.
The proportion of low and medium-yielding environments decreased over time; while high- and very high-yielding environments increased.
The proportion of low- and medium-yielding environments decreased more for the northern latitudes, 45º to 50º N, compared to 35º to 40º and 40º to 45º N latitude groups.
Overall average annual yield gain for the study area from 1987 to 2015 was 2.2 bu/acre per year.