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Steps to optimize corn planting

 by Jeff Coulter, Extension corn agronomist

Successful stand establishment is key to profitable corn production. Consider the following planting guidelines for optimal corn stand establishment.

Planting date

Planting date is one of many factors that can affect corn yield. However, other factors such as the uniformity of emergence, weather conditions during the two weeks before and two weeks after tasseling, hybrid selection, crop nutrition, weed and pest control, and crop rotation typically have a greater effect on yield than planting date. 

Across 26 planting date trials conducted across Minnesota from 2009 to 2016 by the University of Minnesota, corn grain yield was within 1% of the maximum when planting occurred between April 25 and May 12, and yield loss due to delayed planting did not occur until more than 140 GDDs had accumulated since the first planting date (Table 1). However, in years when warm weather arrives earlier than normal and persists, planting in mid-April can produce similar yield if young corn plants are not significantly damaged by a freeze in May.

Table 1. Corn grain yield as affected by planting date across 26 planting date trials conducted across Minnesota from 2009 to 2016, along with the growing degree days (GDDs) accumulated since the first planting date in these trials.

Planting date Grain yield
% of maximum
GDDs accumulated since
1st planting date
April 12-17 94-96 0
April 18-24 97-98 13-18
April 25-May 12 99-100 31-137
May 13-19 97-98 146-208
May 20-25 94-96 219-281
May 26-30 91-93 294-350

Soil temperature

Germination of corn requires that seeds take up 30% of their weight in water and that soil temperature be 50°F or warmer. Risk of stand establishment problems are reduced if corn is planted when soil in the seed zone has reached or is near 50ᵒF and is expected to warm, since seeds can take up water even when soil temperature is less than 50ᵒF. However, if planting is delayed until May, planting should generally begin as soon as soil conditions are suitable, regardless of soil temperature.

It is important to consider the expected weather and soil temperature during the 1 to 2 days after corn planting. This is because imbibitional chilling injury to corn can occur when soil temperature is near 40°F or lower within 1 to 2 days of corn planting and seeds take up cold water. Imbibitional chilling injury occurs because cellular tissues of seeds are less flexible under cold conditions and can rupture when seeds swell due to the uptake of water. However, if soil temperature drops to 40°F or lower beyond 2 days after corn planting, the risk of imbibitional chilling injury is greatly reduced compared to when a similar drop in soil temperature occurs within 1 to 2 days after planting.

Soil Conditions

Avoid pre-plant tillage and planting when soils are wet, as this can negate potential advantages to an earlier planting date. A field is ready for seedbed preparation when soil in the depth of tillage crumbles when squeezed. Tillage of wet soil causes clods, which reduce seed-to-soil contact by creating air pockets between soil and seed. Excellent seed-to-soil contact is essential for rapid uptake of moisture by seeds and uniform emergence. Tillage of wet soil also creates a compacted layer below the depth of tillage, which can restrict root development.

Sidewall compaction can occur when planter disc openers cut through wet fine-textured soil, resulting in compacted soil around the seed that is difficult for roots to penetrate after the soil dries. Seed furrows can also open after planting in wet fine-textured soils, resulting in poor seed-to-soil contact, uneven emergence, and a low plant population.

It is important to avoid more pre-plant tillage than necessary. Excessive pre-plant tillage reduces soil moisture in the seed zone. It can also lead to crusting of the surface soil if there are high-intensity rains, which can restrict corn emergence. Excessive pre-plant tillage also increases the risk of soil wind erosion. Blowing sand-sized soil particles after corn emergence can cut off or injure corn seedlings.

Conserve moisture in dry soils

If soils are dry and there is concern that soils may be too dry for successful stand establishment, consider the following tactics to conserve soil moisture if pre-plant tillage is used:

  • Prepare seedbeds close to planting
  • Avoid unnecessary tillage passes
  • Avoid tilling deeper than needed
  • Use a rolling basket to reduce evaporation of soil moisture after tillage

Planting depth

A planting depth of 2 inches is optimal for corn in most situations. Shallow seed placement increases risk of poor nodal root establishment. If soils are very dry, planting as deep as 2.5 inches to reach soil moisture is okay, as long as planting is not early and soil temperature in the seed zone is at least 50ᵒF. Early in the planting process and also when switching to fields with different soil and residue conditions, make sure to dig up planted seed to ensure consistent planting depth and good seed-to-soil contact.

Uniform emergence

A goal of corn production is to have the majority of corn plants emerge at the same time. According to a previous study in southwestern Minnesota, a corn plant that is one leaf stage behind its neighboring plants early in the season will only yield about 80% of normal, while a corn plant that is two leaf stages behind its neighboring plants early in the season will only yield about 50% of normal. For uniform emergence, corn needs adequate and consistent (1) soil moisture in the seed zone, (2) seed-to-soil contact, and (3) soil temperature in the seed zone, along with a lack of crust on the soil surface and soil compaction near the seed. Of these factors, irregular soil moisture in the seed zone is the most common cause of uneven emergence, and it can result from inconsistency in soil conditions, residue, and the depth of seed placement.

Planting rate

Optimal planting rates for grain corn in Minnesota vary somewhat with soil productivity, expected yield, and hybrid, and typically do not differ with row width. Too high of a planting rate generally does not reduce corn yield but can reduce economic net return. For moderate- to high-yielding soils, optimal planting rates for grain corn are typically 34,000 to 36,000 seeds per acre, but can be as high as 38,000 to 40,000 seeds per acre in some cases. 

On non-irrigated drought-prone soils where maximum yields are 130 to 160 bushels per acre, optimal planting rates are generally 30,000 to 33,000 seeds per acre, but can be lower. On non-irrigated drought-prone soils where maximum yields are less than 130 bushels per acre, optimal planting rates are around 27,000 to 30,000 seeds per acre. 

To check optimum planting rates in your fields, consider using test blocks or strips that are planted at 3,000 to 4,000 seeds per acre higher and lower than the planned rate for each planting rate zone in a field, and then measure the yields.

More educational resources on corn production are available at Extension's Corn Production website

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