Objectives
- Pioneer scientists have collected data on corn plant population responses and yield gains to provide better information on hybrid performance. From 1987 to 2016, nearly 200,000 yield and plant population data points were collected from more than 40 locations throughout North America (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, Associate Professor in Crop Production and Cropping Systems at Kansas State University.
- The main objectives of this long-term study were to examine the trend in the agronomic optimum plant density (AOPD) and its relationship to corn yield, and to quantify the contribution of plant density to yield gain during the 1987 to 2016 time period.
Study Description
- Pioneer corn plant population research trials were conducted from 1987 through 2016 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 50,000 plants/acre. 30 to 50 commercially available Pioneer® brand hybrids were included per year.
- Not all hybrids were included at each location and not all locations were included every year.
Figure 1. Locations and yield levels (bu/acre) of plant population studies conducted by Pioneer from 1987 to 2016.
Figure 2. A Pioneer plant population research experiment.
Results
- Across all environments and hybrids, average agronomic optimum plant density increased from 30,500 plants/acre from 1987-1991 to 37,900 plants/acre from 2012 to 2016; a rate of increase of 285 plants/acre/year (Figure 3).
Figure 3. Historical changes in average agronomic optimum plant density over hybrid release year for corn for the entire North America, 1987-2016 period. (Assefa et al., 2018, Scientific Reports Journal).
- The increase in agronomic optimum plant density varied across latitudes from 35º to 50º N latitude, but without showing a consistent trend.
- Agronomic optimum plant density increased to a greater degree over time in higher yielding environments (Table 1).
Table 1. Increases in agronomic optimum plant density by yield level from 1987 to 2016.
* No significant increase in optimum plant density.
- Maximum yield at the agronomic optimum plant density increased from 140 bu/acre from 1987-1991 to over 190 bu/acre from 2012-2016; a rate of increase of 2.23 bu/acre/year (Figure 4).
Figure 4. Maximum corn grain yield at the agronomic optimum plant density by hybrid release year, 1987 to 2016. (Assefa et al., 2018, Scientific Reports Journal).
- The range of the agronomic optimum plant density increased over time from the 1987-1991 period to the 2012-2016 period. This new finding shows that modern hybrids not only need more plants in order to attain higher yields, but also that the stability of modern hybrids has increased relative to older hybrids (Figure 5).
- Evaluating the six five-year periods from 1987 to 2016, the increase in yield at the agronomic optimum plant density over time exceeded that which can be attributable solely to the increased plant density, indicating that yield per plant became less sensitive to the increases in plant density.
- Further studies should be focused on improving the understanding of the changes over time in yield components at varying crowding stress levels.
- Overall, plant density contributed to 9-18% of the corn yield gain during the last 30 years of crop improvement.
- To the extent of our knowledge, this is the first time that corn yield gain is reported at a regional-scale (multi-year and -location). Overall, average corn yield gain at the agronomic optimum plant density was primarily driven by an increase in the frequency of high-yielding environments (150-195 bushels per acre), with exception of the low-yielding sites.
Figure 5. Agronomic optimum plant density (averaged over all Pioneer® brand hybrids) over the six 5-year time periods from 1987 to 2016. Shaded bars show the increase in agronomic optimum plant density range from the earliest time period in the study to the most recent.
Conclusions
- Agronomic optimum plant density increased during the last 30 years by nearly 7,500 plants/acre and corn yields at agronomic optimum plant density increased by more than 50 bu/acre.
- Modern hybrids not only have a higher agronomic optimum plant density but the range around the optimum level has widened over time, indicating a greater degree of stability for modern relative to older corn hybrids.
- Corn yield gain was achieved not only via improvement in tolerance to plant density, but there is sufficient evidence that confirms changes in per-plant yield, reflected in a more favorable kernel number/weight ratio.
Author: Dr. Ignacio Ciampitti, Associate Professor Cropping Systems Specialist, Department of Agronomy, Kansas State University
Based on: Assefa Y, Carter P, Hinds M, Bhalla G, Schon R, Jeschke M, Paszkiewicz S, Smith S, and Ciampitti IA (2018) Analysis of long term study indicates both agronomic optimal plant density and increase maize yield per plant contributed to yield gain. Scientific Reports 8, 4937.
The foregoing is provided for informational use only. Please contact your Pioneer sales professional for information and suggestions specific to your operation. 1987-2016 data are based on average of all comparisons made in over 40 locations through Dec. 1, 2016. Multi-year and multi-location is a better predictor of future performance. Do not use these or any other data from a limited number of trials as a significant factor in product selection. Product responses are variable and subject to a variety of environmental, disease, and pest pressures. Individual results may vary.
August 2018