Planting Depth and Landscape Position Effects on Corn Emergence

• The effects of landscape position and corn planting depth on corn emergence differed between the two years of the study due to differing weather conditions after planting.
• Deeper planting was generally favorable for emergence in 2018 when temperatures after planting were warm, but unfavorable in 2019 when temperatures were colder.
• The summit position had slower emergence in 2018 compared to other landscape positions, while corn on the backslope was slowest to emerge in 2019.
• Despite significant effects of planting depth on emergence characteristics, yield was not ultimately affected by planting depth in this study.

• Studies throughout the U.S. have found optimum corn seeding depths to vary from 1 to over 3 inches depending on soil texture, moisture, temperature, seeding date, and other factors.
• University Extension guidelines in the U.S. Corn Belt commonly recommend seeding depths of 1.5 to 2.5 inches.
• Specific seeding depth recommendations within the 1.5- to 2.5-inch zone are often based on soil texture and moisture conditions.
• Claypan soils in Missouri possess landscape position and topsoil depth variations that result in complex hydrologic features.
• Site-specific management of corn seeding depth has the potential to homogenize stands and increase corn yield on variable soils within Missouri fields.
• A field study was conducted by Dr. Newell Kitchen, USDA-ARS, and Stirling Stewart, Lance Conway, and Dr. Matt Yost of the University of Missouri as a part of the Pioneer Crop Management Research Awards (CMRA) Program to determine the influence of seeding depth and landscape position on corn emergence and grain yield.

• Plot studies were conducted in 2018 and 2019 near Columbia, MO, at the University of Missouri Bay Farm Research Facility on an upland alfisol soil with a claypan horizon.
• Three landscape positions, summit, back slope, and foot slope, were identified within a single field and used for the study. 
• Plots at each landscape position were planted to four targeted seeding depths, 1.5, 2.0, 2.5, and 3.0 inches.
• Plots were four rows by 30-ft long, planted at 30-inch row spacing.
• The study was planted on April 26 in 2018 and on April 9 in 2019, with good soil moisture in both years.
• All plant measurements were taken for both studies from two 10-ft long sections from adjacent rows in each plot. Plant emergence was monitored and recorded daily for each plant.
• Three response measurements were generated from the collected emergence data.
  • Emergence rate: Total time required from planting to 90% emergence
  • Emergence window: Time between first emergence and 90% emergence
  • Emergence percent: Fraction of emerged seedlings from total seed planting

• Varied weather events created conditions ranging from conducive to problematic for germination uniformity.
  • In both 2018 and 2019, average air temperatures at planting were within 50-59°F.
  • In 2018, temperatures warmed after planting, while in 2019 they got cooler, preventing the soil from warming.
  • Low soil temperatures in 2019 slowed seed germination processes and resulted in seedling damage.

Corn Emergence Rate

• Emergence rate was impacted differently each year for both landscape position and planting depth (Table 1).
  • All landscape positions required an average of 3 additional days to reach 90% emergence in 2019 vs 2018 due to colder soil temperatures (Figure 1).
  • In 2019, the back slope required an additional 1.1 days to reach 90% emergence. Poor drainage and an eroded A horizon contributed to a soil environment with excessive moisture and poor root development.
  • In 2018, the two deepest planting depths emerged on average about one day ahead of the shallowest planting depth (Figure 2).
  • The opposite trend was observed in 2019. Emergence was delayed with increased planting depth. Compared to the two shallowest depths, the emergence rate was delayed 3.5 days for the deepest planted seed.

Table 1. Analysis of variance for corn stand establishment characteristics from 2018 to 2019 on landscape position study.

Corn Emergence Window

• Emergence window had a similar response to emergence rate, with landscape position and planting depth factors differing by year.
  • Deep planting was beneficial for emergence uniformity in 2018. Emergence window in 2018 was approximately 1 day longer for shallow planted corn (Figure 3).
  • The opposite was the case in 2019 with a longer emergence window for deeper planted corn of 1.7 days compared to shallower planted corn.
• The contrast between years was most pronounced at deeper planting depths, and can be explained by soil temperatures.
• Of the three landscape positions, only the back slope differed in emergence window, and that was for 2019 only. For this year, the back slope had an emergence window 1.2 days greater than the other two positions.
• Under cool conditions, seed planted deeper on the back slope position would undoubtedly be impacted more by the claypan effect since the seed would be closer to the argillic horizon.

Corn Emergence Percent

• In 2018 the foot slope experienced the lowest emergence percent of the three landscape positions. In this year, with warm conditions and adequate moisture, it is unclear what led to the greater emergence at the back slope compared to the foot slope position.
• In 2019, crop residue was slightly more abundant at the summit position compared to the eroded back slope and foot slope positions.
• The summit was the only landscape position to have reduced emergence compared to the warmer 2018 germination period, which suggests residue had a greater impact than cool temperatures on emergence percent.

Corn Yield

• Average corn yield was greater at the foot slope than the other two landscape positions; however, yield was not significantly affected by planting depth (Table 2).

Figure 1. Landscape position effects on emergence rate by year. Lower-case letters indicate significant differences within years and uppercase letters indicate significant differences across years.

Figure 2. Planting depth effects on emergence rate by year. Lower-case letters indicate significant differences within years and uppercase letters indicate significant differences across years.

Figure 3. Planting depth effects on emergence window by year. Lower-case letters indicate significant differences within years and uppercase letters indicate significant differences across years.

Table 2. Plot yield from all depths and landscape positions averaged across years. Letters indicate differences between landscape positions.

• All three emergence performance metrics were uniquely affected each year by landscape position.
• Emergence timeliness and uniformity were also impacted differently each year by planting depth.
• Careful attention to conditions in uplands fields like the one used in this study is necessary, as emergence performance can vary substantially over changing landscape positions, planting depths, and growing seasons.