Growing Degree Days vs. Calendar Days – How Long Will Emergence Take?

Source: Alexander Lindsey, Greg LaBarge, OSU Extension

When we examine crop emergence post-planting, two factors can impact speed of emergence – soil moisture content and soil temperatures. If soil temperatures are lower, it can take more calendar days for emergence to occur meaning rowing corn may take a little more time. In the Ohio Agronomy Guide, emergence should begin to occur after approximately 100 air GDDs.

A difference in 10 degrees in temperature can dramatically affect how quickly crops will emerge. For example, at a temperature of 60 degrees F heat unit accumulation per day would be 60 F – 50 (base temperature for growth) = 10 GDDs. If it takes 100 GDDs to start to see emergence, at this rate it would take 10 calendar days to see the crop start to emerge. If temperatures are 70 degrees F, heat unit accumulation per day would be 70 F – 50 = 20 GDDs. This would shorten the emergence window to 5 calendar days instead, resulting in more rapid emergence from planting.

Figure 1. Emerged corn on May 6, 2021 planted April 19 near London, OH.

In recent work from Nemergut et al. (2021), researchers from OSU observed emergence starting at 110 to 120 soil accumulated GDDs (base of 50 degrees F) for corn, which equated to first emergence observed in 4 or 5 days after planting. Some of the difference in calendar date for emergence (though GDD accumulation was similar) was because planting depth was changed, and the 1” planting accumulated GDDs faster than the 2” and 3” planting depths. These studies though were planted in May or early June (2019 wet spring delayed planting), and daily accumulated GDDs was higher than we might expect if planted in late April. Soil accumulated GDDs have been discussed above, and these could vary slightly compared to air accumulated GDDs (calculated using air temperatures). In the work referenced above, accumulated air GDDs in the first four days post-planting were 106-118 GDDs, slightly less than the soil accumulated GDDs.

If you want to predicate emergence on your farm, the GDD calculator found at https://mrcc.illinois.edu/U2U/gdd/ is a useful tool. It is a two-step process, first find your location on the map, then enter your planting date. The graph will display accumulated GDD’s for your location. Example output in Figure 2 shows GDD accumulation from an April 19, 2021 planting date near London, OH in Madison County. By May 6 the accumulated GDD was 138 and the emerging corn is shown in Figure 1. The GDD calculator can be used to predict growth stage throughout the growing season. This is a handy to time when scouting and management decisions should be made.

Figure 2. GDD accumulation from April 19 to May 6, 2021 near London, OH.

As the days turn cooler, don’t be surprised if the crops don’t pop out of the ground quickly due to lower soil temperatures. If emergence is still not observed after two weeks, it may be worth checking the field to see if other issues may be affecting emergence.

Soil Moisture & Corn Seed Depth

Source: Dr. Bob Nielsen, Purdue Univ.

Bottom Line: Uniformly adequate soil moisture at seeding depth is important for assuring rapid and uniform germination of a newly planted corn crop. Take time to assess soil moisture at your selected seed depth on the day of planting. If soil moisture is not available or unevenly available at your normal seeding depth, then consider planting deeper than normal if soil moisture is available at those deeper settings.

Uniformly adequate soil moisture at seeding depth is important for assuring rapid and uniform germination of a newly planted corn crop. Take time to assess soil moisture at your selected seed depth on the day of planting. If soil moisture is not available or unevenly available at your normal seeding depth, then consider planting deeper than normal if soil moisture is available at those deeper settings.

Choice of seeding depth for corn is often paid scant attention by growers during the rush of planting their crop. Human nature being what it is, we tend to simply leave the planter’s depth control setting at the same position as it was in previous years. While it is true that a seeding depth of 1.5 to 2 inches is a fairly all-purpose range that works well in most situations, certain conditions merit more attention to seeding depth, the most common factor being soil moisture.

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Corn, Soybean and Wheat Enterprise Budgets – Projected Returns for 2021 Increasing Fertilizer Prices May Force Tough Decisions

Source: Barry Ward, John Barker, OSU Extension

The profit margin outlook for corn, soybeans and wheat is relatively positive as planting season approaches. Prices of all three of our main commodity crops have moved higher since last summer and forward prices for this fall are currently at levels high enough to project positive returns for 2021 crop production. Recent increases in fertilizer prices have negatively affected projected returns. Higher crop insurance costs as well as moderately higher energy costs relative to last year will also add to overall costs for 2021.

Production costs for Ohio field crops are forecast to be modestly higher compared to last year with higher fertilizer, fuel and crop insurance expenses. Variable costs for corn in Ohio for 2021 are projected to range from $386 to $470 per acre depending on land productivity. Variable costs for 2021 Ohio soybeans are projected to range from $216 to $242 per acre. Wheat variable expenses for 2021 are projected to range from $166 to $198 per acre.

Returns (excluding government payments) will likely be higher for many producers depending on price movement throughout the rest of the growing year. Grain prices currently used as assumptions in the 2021 crop enterprise budgets are $4.30/bushel for corn, $11.55/bushel for soybeans and $6.25/bushel for wheat. Projected returns above variable costs (contribution margin) range from $216 to $434 per acre for corn and $284 to $509 per acre for soybeans. Projected returns above variable costs for wheat range from $193 to $342 per acre. As a reminder, fixed costs (overhead) must be paid from these returns above variable costs. Fixed costs include machinery ownership costs, land costs including rent and payment for owner operator labor and management including other unpaid family labor.

Fertilizer prices continue to increase.  If you have not checked fertilizer prices lately, be prepared for some sticker shock. Producers with some fertilizer purchased and stored or pre-priced prior to recent price increases will likely see a healthier bottom line this upcoming crop year.

Those with little or no fertilizer pre-purchased and stored or pre-priced may want to consider using P and K buildup to furnish crop needs this year in anticipation of possibly lower prices in the future.  Now may be a good time review your fertilizer plans as you are considering how to best utilize your financial resources in 2021.

  • Use realistic yield goals.  Yield goals vary by field.  Each field has unique characteristics that can impact yield.
  • Utilize crop removal rates to determine crop nutrient needs.  Crop removal rates can be found in the new Tri-State Fertilizer Recommendations for Corn, Soybeans, Wheat, and Alfalfa (Tables 15 and 16), available at your local Extension Office.
  • Start with a recent soil test.  If your soil test levels are in the maintenance range or higher, 2021 may be a good year to “borrow” from your soil nutrient bank.

As an example, a 150-bushel corn crop will remove about 55 pounds of P2O5 per acre in the harvested grain.  This would result in a reduction in the soil test level of approximately 3 ppm.

Current budget analyses indicates favorable returns for soybeans compared to corn but crop price change and harvest yields may change this outcome. These projections are based on OSU Extension Ohio Crop Enterprise Budgets. Newly updated Enterprise Budgets for 2021 have been completed and posted to the Farm Office website: https://farmoffice.osu.edu/farm-mgt-tools/farm-budgets