Lessons From Early Planted Corn Emergence Trials
Crop Insights by Imad Saab, Pioneer Research Scientist
- The optimal soil temperature for corn emergence is around 85 F. Thus, corn is almost always planted into suboptimal conditions in the U.S. and Canada.
- Early planting increases the likelihood that seeds will be exposed to cold, wet soils that can reduce stand establishment and yield.
- Pioneer annually conducts early planted stress emergence trials in multiple locations throughout North America to test and select hybrids for early season stress tolerance.
- Results from multiyear trials show that emergence is maximized when soil temperatures at planting are at or greater than 50 F with a warming trend. On the other hand, emergence is reduced when seeds are planted into colder soils or when planting is followed by a cold front.
- Growers can protect against stand (and yield) loss by monitoring soil temperature at planting depth and delaying planting until soils approach 50 F and are sufficiently dry to minimize compaction. Growers should also avoid planting directly ahead of a cold front to allow for germination to begin under favorable conditions.
- No-till growers should be aware of additional stresses caused by residue including cooler soils, physical impedance and uneven planting depth, which can reduce stand uniformity and lead to "runts." Row cleaner attachments are recommended in heavy residue fields to mitigate these factors.
- Growers should make use of Pioneer's stress emergence and high residue suitability scores in choosing hybrids for early planting and high residue fields.
- Growers should watch out for increased pressure of early season insects especially in high residue fields and ensure their stands are protected with the right insecticide seed treatments.
The recommended corn planting dates in the central Corn Belt are mid-April through early May, and in northern areas, early through mid-May. In Iowa, for example, extension research results show that optimum yields are achieved with planting dates between April 20 and May 5, and no later than mid-May. However, growers in most areas, including traditionally colder northern states have been planting much earlier than recommended. For example, in recent years many growers in South Dakota have taken advantage of dry weather in April to complete corn planting several weeks ahead of the early to mid-May planting date recommended by regional extension agronomists.
These early planting dates carry increased risk of stand loss due to cold stress. This is especially true in northern regions where brief periods of warm weather in April are often followed by extended cold or snow (Figure 1). Early planting also carries increased risk of stand losses due to a killing frost. For example, widespread frost in April 2005 necessitated replants in many central Iowa and Illinois areas.
Figure 1. Planting corn in southern Minnesota, April 30, 2008. Challenges include crop residue as well as the snowdrift.
The optimal temperature for corn emergence is around 85 F. The rate of emergence is greatly reduced at lower temperatures and is effectively halted around 50 F. The degree to which stand establishment is adversely affected by cold temperatures is largely determined by soil temperatures during imbibition and seedling emergence.
Early Soil Temperatures Vary Widely
Spring soil temperatures can vary greatly year to year. Thus, growers should pay closer attention to soil temperatures and field conditions rather than calendar date when choosing a planting date. Soil temperatures at planting in combination with near- to moderate-term weather trends have profound effects on the probability of establishing optimal stands and achieving maximum yields.
Pioneer researchers recorded average nighttime soil temperatures at planting depth at several emergence trial locations in 2008 (Figure 2). Similar data collected from multiple years and locations can provide an understanding of the impact of these factors.
Figure 2. Average late-April nighttime soil temperatures recorded at 2 inch depth in a sample of Pioneer stress emergence testing locations.
Generalized Relationship of Soil Temperature to Stand Establishment
Figure 3 demonstrates in a generalized fashion the relationship between soil temperature and final stand.
Figure 3 . Relationship of soil temperature at planting depth (14-day average after planting) to final stand. Data from six Pioneer early-planted locations, 2008.
These locations were spread across the Midwest US and Canada and included no-till, corn-on-corn and clean-till soils. The entry list of hybrids tested closely represented the majority of commercial products sold in North America. In all locations, the crop was planted into moisture, which allowed seeds to begin imbibition immediately. In addition to the soil moisture available at planting, several locations received snow or cold rain shortly after planting.
The results demonstrated that locations where the average soil temperature was above 50° F for a two-week period after planting had much higher final stands than locations where soils remained at 50° F or below for the same period. It should be noted that these locations were chosen and managed for maximum seedbed stress to enhance selection for superior hybrids. As such, these fields were intentionally more stressful than commercial fields in the area with a resulting magnification of the impact of cold soils. Nevertheless, the results demonstrate the advantage of planting into warmer soils on stand establishment and yield.
It is strongly recommended that growers routinely measure soil temperature to better understand its impact on stand establishment under their particular soil and management conditions. General planting date recommendations based on industry or university trials cannot account for all variables (e.g., residue level and soil type) that affect the crop's response to early cold stress.
Impact of Residue
High residue farming offers several advantages including reduced input and labor costs and improved water use efficiency in some regions. However, high residue fields present additional challenges to corn emergence especially in colder regions or poorly drained soils (Figure 4).
Figure 4. Corn emergence in a no-till corn-after-corn field in Schuyler, Nebraska planted April, 2008.
The more obvious effects of residue relate to slower soil warming and excess water in the seedbed, both of which can further reduce stands in a cold, wet spring. Less obvious, however, is the increased potential for nonuniform emergence and "runts" in high residue fields. The presence of residue clumps in the path of emerging seedlings is a major cause for runt plants in no-till fields. Also, crop residue can make it harder to achieve a uniform planting depth. Nonuniform seed depth contributes to nonuniform emergence and the appearance of runt plants, especially in stressful environments.
Growers planting into residue should consider using a row cleaner attachment on their planters. A row cleaner acts to push aside the residue in a narrow band where the seeds are dropped. This usually contributes greatly to stand establishment by speeding up soil warming near the planted seed and removing physical barriers that block emergence. An example of this is shown in Figure 5 where the residue in the row on the right was effectively managed by the residue cleaners with a resulting improvement in stand establishment and vigor compared to the row on the left which had considerably more residue on top of the row.
Figure 5. Impact of excess residue on top of the row (left) compared to a clean row (right) in an early-planted no-till, corn-after-corn field, 2008.
Understanding and managing early planting risks is a crucial step to achieving a productive stand. Corn is very sensitive to cold stress in the early season. The damage to stand establishment is greatest if the crop is planted into cold soil (typically below 50 F) or if planting is followed by snow, cold rain or an extended cold spell. Of all management practices that affect stand establishment and in turn, yield, the planting date decision often has the greatest impact.
Pioneer has conducted early planted research trials over several years across a wide range of geographies, soil types and tillage systems. Results from these as well as public research trials indicate that emergence is maximized when soil temperatures are 50 F or above at planting and followed by a warming trend through emergence. For that reason, growers who plant early should pay close attention to soil temperature, moisture and the near-term forecast. Another key to facilitate rapid and uniform emergence is to manage crop residue in the fall and/or in front of the planter units. Growers should also check behind the planter to ensure they are achieving uniform planting depth and good soil-to-seed contact, and delay planting until the soil is sufficiently dry to minimize compaction.
To help growers manage early season risks, Pioneer provides stress emergence scores and high residue suitability scores for all hybrids offered in North America. Choosing hybrids with higher scores for these traits helps reduce genetic vulnerability to stress brought on by cold soils and high residue environments. Pioneer also offers Cruiser Extreme 250® seed treatment which provides broad defense against disease and insect pests common in early planting. Additional details on stress emergence, high residue suitability and Pioneer seed treatments can be found in several Crop Insights articles referenced below.
The author is grateful to Maria Stoll, Meghan Roche and the staff at Pioneer's research centers for invaluable contributions to the research behind this Crop Insights, and to Steve Butzen, Pioneer Agronomy Information Manager for helpful discussions and critical editorial assistance.
Corn Planting Guide, Iowa State University Extension, 2001.
Suggested Corn Seeding Dates in South Dakota, SD Agricultural Statistical Reporting Service, SDSU Extension Crop Management, South Dakota Sate University.
Thinking About Corn Planting Date and Population, The Bulletin, University of Illinois Extension, IPM Bulletin No. 2, Article 7, 2008.
McLeod, M. and Butzen, S. 2008. Cruiser Extreme® 250 Seed Treatment on Pioneer® brand Corn Hybrids. Crop Insights Vol. 18 No. 16.
DeFelice, M, Carter, P and Mitchell, S. 2006. Influence of Tillage on Corn Yield in the United States and Canada. Crop Insights Vol. 16 No. 2.
Saab, I, 2005. Stress Emergence in Corn. Crop Insights Vol. 15 No. 6.
Saab, I and Butzen, S. 2004. Diagnosing Chilling and Flooding Injury to Corn Prior to Emergence. Crop Insights Vol. 14 No. 4.