Field Facts by Peter Thomison¹, Mark Jeschke² and Steve Butzen³

Key Findings

• Grain yields were about 14% greater for the 1.5-inch and 3-inch planting depths than the 0.5-inch planting depth in 2011, and 40% greater in 2012.
  • The lower yield of the shallow planting was associated with a reduced final stand of about 7000 plants/acre in 2011 and 12,000 plants/acre in 2012.
  • The lower yield of the shallow planting was also associated with 6 to 7 times as many “runt” plants as the other two planting depths.
• Although differences in yield were evident among Pioneer® brand corn products, the three products exhibited similar yield responses to varying planting depths.
• Drought tolerance rating effects could not be separated from hybrid genetic effects in this study. However, there was no evidence that differences in drought tolerance ratings affected product response to planting depth.

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Introduction

Planting depth recommendations for corn in Ohio are 1.5 to 2 inches deep to ensure adequate moisture uptake and seed-to-soil contact. Deeper planting may be recommended as the season progresses and soils become warmer and drier. Planting shallower than 1.5 inches is generally not recommended at any planting date or in any soil type.

When corn is planted 1.5 to 2 inches deep, the nodal roots develop about 0.75 inches below the soil surface. However, at planting depths less than 1 inch, the nodal roots develop at or just below the soil surface (Figure 4). Excessively shallow planting can cause slow, uneven emergence due to soil moisture variation, and rootless corn (“floppy corn syndrome”) later in the season when hot, dry weather inhibits nodal root development (Figure 1). This latter situation has led to the assumption that planting depth may play a role in managing the drought susceptibility of a hybrid.

According to some field agronomists, shallow plantings in-crease stress and result in less developed roots, smaller stalk diameters, smaller ears and reduced yields. However, data substantiating such claims are limited. Growers have also been encouraged to avoid shallow planting depths because it increases the potential for injury from certain preemergent herbicides, although widespread use of safer herbicides (e.g., glyphosate) has probably decreased this effect.

Figure 1. Rootless corn syndrome caused by shallow planting and dry soils conditions.

Background

Ohio growers frequently plant at depths less than 1.5 inches, expecting that seed will emerge more rapidly due to warmer soil temperatures closer to the surface. This is an important consideration, as corn growers across the Corn Belt are planting earlier so they can complete planting before yield potential begins to decrease after the first week of May. Particularly in soils that crust, speed of emergence is critical in order to establish plant stands before heavy rainfalls “seal” the soil surface.

Although previous research has generally documented faster emergence rates with shallower planting depths, the comparisons have often included deeper planting depths than the recommended ranges and results are highly influenced by temperature and rainfall in the given season. Recent studies comparing planting depths that are within the depth ranges commonly used by growers are limited, and none have attempted to compare hybrid differences between planting depths.

Corteva Agriscience has worked to introduce hybrids with improved drought tolerance in order to provide yield stability on variable and droughty soils. Hybrids with higher levels of drought tolerance may provide improved yield stability in shallow-planted situations while also providing improved performance at normal planting depths, though this has not been documented. Improving our understanding of newer hybrid responses to planting depth across planting dates and over different soil types may help improve our understanding of hybrid management and positioning. Incorporation of differing planting dates and soil types will allow a more robust analysis of the impact of temperature, soil water holding capacity and crusting potential over the course of the study.

Study Objectives

The objectives of this research study⁴ were:

• to evaluate the effect of planting depth on stand establishment of Pioneer® brand corn products,
• to evaluate the grain yield response of corn products with different drought tolerance ratings to varying planting depths,
• to assess if planting depth effects varied across growing environments that differed by soil type and planting date.

Study Description

Locations: This study was conducted in conjunction with the 2011 Ohio State University Ohio Corn Performance Test (OCPT) and established at ten locations (Hebron, Washington Court House, S. Charleston, Greensville, Van Wert, Hoytville, Upper Sandusky, Bucyrus, Wooster, and Beloit).

Plot Design: The experiment was replicated 3 times in a randomized complete block arranged in split-plot layout. The main plot was planting depth and subplot was hybrid. Plot size was four 30-inch rows 25 feet in length. Force 3G soil insecticide was applied in a T-band to all plots.

Hybrids and Planting Depth Treatments: Three Pioneer^® brand corn products, P0965AM1^TM (AM1, LL, RR2, 108 CRM), P0891AM1^TM (AM1, LL, RR2, 109 CRM), and 35H42 (HX1, LL, RR2, 107 CRM) were planted at three planting depths (0.5, 1.5, and 2.5 to 3 inches). The drought scores for the three products were 8, 7, and 6, respectively. The Pioneer drought rating scale is from 1 to 9 (9 = best).

Seeding Rate, Measurements: Plots were planted at a rate of 34,000 seeds/acre. Measurements collected during the growing season included early stand, late emergers (“runts”), stalk diameter, final stand, ear weight, “nubbins”, grain yield, stalk and root lodging, and test weight. Weather data at each site were recorded.

Applied Questions

How did planting depth affect corn yields?

2011: Grain yields, averaged across locations and hybrids, were 13% and 15% greater for the 1.5- and 3-inch planting depths, respectively, than the 0.5-inch planting depth (Figure 2).

• At eight of the 10 sites, yields of the 3-inch planting depth treatment exceeded those of the 0.5-inch planting depth treatment (data not shown).
• At five of the 10 sites, yields of the 1.5- and 3-inch treatments were similar; the 1.5-inch treatment out-yielded the 3-inch treatment at one site (data not shown).

Figure 2. Corn yield response to planting depth in 2011 and 2012.

2012: Grain yields, averaged across locations and hybrids, were 40% greater for the 1.5- and 3-inch planting depths than the 0.5-inch planting depth (Figure 2).

• At nine of the 10 sites, yields of the 1.5-inch and 3-inch planting depth treatments were greater than those of the 0.5-inch planting depth (data not shown).
• At six of the 10 sites, yields of the 1.5-inch and 3-inch treatments were similar (data not shown).

Did planting depth affect stand establishment, and was this associated with yield effects?

2011: The lower yield of the shallow planting treatment in Figure 2 was associated with a reduced final stand - 27,200 plants/acre for the 0.5-inch depth vs. 34,200 and 34,000 plants/acre for the 1.5-inch and 3-inch planting depths, respectively (Figure 3).

• The lower yield was also associated with a greater % of “runts” – 28% for the 0.5-in. depth vs. 5% and 4% for the 1.5-inch and 3-inch planting depths, respectively (data not shown).

Figure 3. Harvest stand response to planting depth in 2011 and 2012.

2012: The lower yield of the shallow planting treatment was associated with a lower final stand - 19,500 plants/acre for the 0.5-inch depth vs. 32,000 and 30,900 plants/acre for the 1.5-inch and 3-inch planting depths, respectively (Figure 3).

• The lower yield was also associated with a greater % of “runts” – 31% for the 0.5-inch depth vs. 6% and 3% for the 1.5-inch and 3-inch planting depths, respectively.

Figure 4. Planting depth (2.5” on left to 0.5” on right) determines the placement of nodal roots, which are developing too near the soil surface in shallow-planted corn plant at right.

Did corn products differ in their yield response to planting depth?

Although differences in yield were evident among hybrids, the three hybrids exhibited similar yield responses to varying planting depth (Figure 5).

• Averaged across locations, the yield of P0965AM1™ exceeded that of the other two hybrids by about 11 to 15 bu/acre at each planting depth.

Figure 5. Corn product yield response to planting depth in 2011 and 2012.

Did differences in hybrid drought tolerance ratings affect yield response to planting depth?

Drought tolerance rating effects could not be separated from hybrid genetic effects in this study. However, similar to the prior question, there was no evidence that differences in hybrid drought tolerance ratings among the hybrids affected response to planting depth (Figure 5).

• P0965AM1™, the hybrid with highest drought tolerance score, was consistently higher yielding than the other two hybrids at all planting depths.

Credits

¹Peter Thomison, Extension Specialist, Corn Production, The Ohio State University, Columbus, Ohio.

²Mark Jeschke, Agronomy Research Manager, Corteva Agriscience, Johnston, Iowa.

³Steve Butzen, Agronomy Information Manager, Corteva Agriscience, Johnston, Iowa.

⁴This research study was conducted by Dr. Peter Thomison, Ohio State University as a part of the Pioneer Crop Management Research Awards (CMRA) Program. This program provides funds for agronomic and precision farming studies by university and USDA cooperators throughout North America. The awards extend for up to four years and address crop management information needs of Pioneer agronomists, sales professionals, and customers.

AM1 - Contains the Optimum^® AcreMax^® 1 Insect Protection System with an integrated corn rootworm refuge solution includes HXX, LL, RR2. Optimum AcreMax 1 products contain the LibertyLink^® gene and can be sprayed with Liberty^® herbicide. The required corn borer refuge can be planted up to half a mile away. HX1 - Contains the Herculex^® 1 Insect Protection gene which provides protection against European corn borer, southwestern corn borer, black cutworm, fall armyworm, western bean cutworm, lesser corn stalk borer, southern corn stalk borer, and sugarcane borer; and suppresses corn earworm. LL - Contains the LibertyLink^® gene for resistance to Liberty^® herbicide. RR2 - Contains the Roundup Ready^® Corn 2 gene that provides crop safety for over-the-top applications of labeled glyphosate herbicides when applied according to label directions. Herculex^® Insect Protection technology by Dow AgroSciences and Pioneer Hi-Bred. Herculex^® and the HX logo are registered trademarks of Dow AgroSciences LLC. Liberty^®, LibertyLink^® and the Water Droplet Design are trademarks of Bayer. Roundup Ready^® is a registered trademark used under license from Monsanto Company.

PIONEER^® brand products are provided subject to the terms and conditions of purchase which are part of the labeling and purchase documents. 2011-2012 data are based on average of all comparisons made in 10 locations through Dec 31, 2012. 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.

The foregoing is provided for informational use only. Please contact your Pioneer sales professional for information and suggestions specific to your operation. Product performance is variable and depends on many factors such as moisture and heat stress, soil type, management practices and environmental stress as well as disease and pest pressures. Individual results may vary.