Estimating Corn Yield

According to the latest Ohio Crop Weather Report 94% of the Ohio corn crop is silking, 6 percentage points ahead of the 5-year average.  39% of the crop is in the dough stage and 1 percent of the Ohio corn crop is dented.

This time of year many of us begin to think about our potential corn yield.  The most popular yield estimator is the  THE YIELD COMPONENT METHOD.  This procedure was developed by the Agricultural Engineering Department at the University of Illinois. The principle advantage to this method is that it can be used as early as the milk stage of kernel development, a stage many Ohio corn fields have probably achieved. The yield component method involves use of a numerical constant for kernel weight which is figured into an equation in order to calculate grain yield. This numerical constant is sometimes referred to as a “fudge‑factor” since it is based on a predetermined average kernel weight. Since weight per kernel will vary depending on hybrid and environment, the yield component method should be used only to estimate relative grain yields, i.e. “ballpark” grain yields. When below normal rainfall occurs during grain fill (resulting in low kernel weights), the yield component method will OVERESTIMATE yields. In a year with good grain fill conditions (resulting in high kernel weights) the method will underestimate grain yields.

In the past, the YIELD COMPONENT METHOD equation used a “fudge factor” of 90 (as the average value for kernel weight, expressed as 90,000 kernels per 56 lb bushel), but kernel size has increased as hybrids have improved over the years. Dr. Bob Nielsen at Purdue University suggests that a “fudge factor” of 80 to 85 (85,000 kernels per 56 lb bushel) is a more realistic value to use in the yield estimation equation today. For more on this check http://www.agry.purdue.edu/ext/corn/news/timeless/YldEstMethod.html.

Step 1. Count the number of harvestable ears in a length of row equivalent to 1/1000th acre. For 30‑inch rows, this would be 17 ft. 5 in.

Step 2. On every fifth ear, count the number of kernel rows per ear and determine the average.

Step 3. On each of these ears count the number of kernels per row and determine the average. (Do not count kernels on either the butt or tip of the ear that are less than half the size of normal size kernels.)

Step 4. Yield (bushels per acre) equals (ear #) x (avg. row #) x (avg. kernel #) divided by 85.

Step 5. Repeat the procedure for at least four additional sites across the field. Keep in mind that uniformity of plant development affects the accuracy of  the estimation technique.

The more variable crop development is across a field, the greater the number of samples that should be taken to estimate yield for the field.

Example: You are evaluating a field with 30‑inch rows. You counted 29 ears (per 17′ 5″ = row section). Sampling every fifth ear resulted in an average row number of 16 and an average number of kernels per row of 33. The estimated yield for that site in the field would be (29 x 16 x 33) divided by 85, which equals 180 bu/acre.

Corn Growth & Development – R3 Milk

Today managing your corn crop requires knowledge of the different growth stages of the corn plant.  Growth stage identification is critical for scouting and proper timing of fertilizer and pesticide applications.

R3 – Milk

The R3 (Milk) stage occurs about 18 – 22 days after silking.  At this stage the outside of the kernel is colored yellow while the inside is white.  The kernel contains a “milky” white fluid that will explode when pressure is applied.  Kernel moisture content is approximately 80% and starch is beginning to accumulate in the kernel.

Management/Scouting: Scout for drought symptoms.  Stress can still cause kernel abortions from the ear tip downward.  Insects: Corn Earworm, Corn Rootworm adults and Japanese Beetles Diseases: Eyespot, Gray Leaf Spot, Norther Leaf Blight, Southern Leaf Blight and Tar Spot

Photo Source: Corn Growth & Development, Iowa State University

Corn Growth & Development – R2 Blister

Today managing your corn crop requires knowledge of the different growth stages of the corn plant.  Growth stage identification is critical for scouting and proper timing of fertilizer and pesticide applications.

R2 – Blister

The R2 (blister) stage occurs about 10 – 12 days after silking.  At this stage the kernel is visible and resembles a blister.  The kernel is filled with clear fluid, the embryo is barely visible and it is at about 85% moisture.

Kernels are in a rapid period of grain-fill.  Rapid and steady grain-fill will continue through R6.  If severe stress occurs now or during R3, kernel abortion will occur from the tip of the ear downward.  Kernel abortion will continue until the plant has has enough carbohydrates for the remaining kernels.

Silks outside the husk leaves are drying and changing in color from tan to light brown.  The silks will naturally detach from their kernels following fertilization.

Kernel Set Scuttlebutt

Source: Dr. Bob Nielsen, Purdue

The post-pollination scuttlebutt overheard in coffee shops throughout Indiana during late summer often revolves around the potential for severe stress that might reduce kernel set or kernel size in neighborhood cornfields. Growers’ interest in this topic obviously lies with the fact that the number of kernels per ear is a rather important component of total grain yield per acre for corn.

Poor kernel set, meaning an unacceptably low kernel number per ear, is not surprising in fields that are obviously severely stressed by drought, but can also occur in fields that otherwise appear to be in good shape. Good or poor kernel set is determined from pollination through the early stages of kernel development; typically 2 to 3 weeks after pollination is complete.

Problems with kernel set stem from ineffective pollination, ineffective fertilization of the ovaries, kernel abortion, or all three. Distinguishing the symptoms is easy. Determining the exact cause of the problem is sometimes difficult.

Potential Yield Loss

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Soybean Vegetative Growth Stages- VC vs V1

By: Laura Lindsay, OSU

Across the state, soybean growth and development is variable, ranging from early vegetative stages to flowering. However, there has been some confusion regarding the identification of the VC and V1 growth stages. This confusion is mostly due to two definitions of V1…that actually mean the same thing. The Fehr and Caviness Method (1977) is based on the number of nodes that have a fully developed leaf, whereas Pederson (2009) focuses more on leaf unrolling so that the leaf edges are no longer touching. The VC definition for both methods is the same, but the differences start to appear between the methods at V1. Fehr and Caviness define V1 as “fully developed leaves at unifoliolate nodes,” which also means that there is “one set of unfolded trifoliolate leaves unrolled sufficiently, so the leaf edges are not touching.” This second definition is common in extension publications (Pedersen, 2009).

Soybean growth stages are described in the OSU Corn, Soybean, Wheat, and Forages Field Guide (available for purchase here: https://extensionpubs.osu.edu/corn-soybean-wheat-and-forages-field-guide-pdf/). A visual guide to soybean staging is available as a pdf from Dr. Shawn Conley at the University of Wisconsin-Madison (https://coolbean.info/library/documents/2017_Soybean_GrowthDev_Guide_FINAL.pdf).

Recommendations for Soybeans Planted in June

Source: Laura Lindsey, The Ohio State University

While progress is way ahead of last year, soybean planting is spilling into June. (According to USDA NASS, 53% of soybean acreage was planted by May 24, 2020. Last year, at the same time, only 11% of soybean acreage was planted.) As planting continues into June, farmers may want to consider adjusting their cultural practices:

Row spacing. Soybean planted in narrow rows (7.5 or 15-inch row width) generally yields higher than soybean planted in wide rows (30-inch). The row spacing for June-planted soybeans should be 7.5 to 15 inches, if possible. Row width should be narrow enough for the soybean canopy to completely cover the interrow space by the time the soybean plants begin to flower. The later in the growing season soybeans are planted, the higher the yield increase due to narrow rows.

Seeding rate. Higher seeding rates are recommended for June planting dates. The final (harvest) population for soybean planted in June should be 130,000 to 150,000 plants/acre. (For May planting dates, a final stand of 100,000 to 120,000 plants/acre is generally adequate.)

Relative maturity. Plant the latest maturity variety that will reach physiological maturity before the first killing frost. This is to allow the plants to grow vegetatively as long as possible to produce nodes where pods can form before vegetative growth is slowed due to flowering and pod formation. The recommended relative maturity ranges are shown in the table below.

 

Cold Weather Impact on Corn and Soybean

Alexander Lindsey, Laura Lindsey – The Ohio State University

In Ohio, between May 9 and 10, temperatures were as low as 26°F with some areas even receiving snow. The effect on corn and soybean depends on both temperature, duration of low temperature, and growth stage of the plant. The soil can provide some temperature buffering capacity, especially if soil is wet. Water is approximately 4x more resistant to temperature changes than air or dry soil, and thus will buffer the soil from experiencing large temperature changes as air temperatures drop. Deeper planted seeds may also be more resistant to large temperature swings.

Imbibitional chilling. Imbibitional chilling may occur in corn and soybean seeds if the soil temperature is below 50°F when the seed imbibes (rapidly takes up water from the soil, usually 24 hours after planting). Imbibitional chilling can cause reductions in stand and seedling vigor. If seeds were planted into soil at least 50°F (and have imbibed), the drop in temperature is not likely a problem if the plants have not yet emerged from the soil.

Corn after germination. The growing point of corn is below the soil surface until the V6 growth stage, and therefore is protected from low temperatures to some extent. However, if the soil temperature falls below 28°F, this can be lethal to corn. Temperatures between 28 to 32°F may result in frost damage, and both the temperature and duration will affect the severity of damage. Between May 9 and May 10, the minimum soil temperature at a 2-inch depth was 38°F at the Northwest Agricultural Research Station in Wood County, 44°F at the Ohio Agricultural Research and Development Center in Wayne County, and 58°F at the Western Agricultural Research Station in Clark County.

Soybean after germination. The growing point of soybean is above the ground when the cotyledons are above the soil surface. If damage occurs above the cotyledons, the plant will likely recover. If damage occurs below the cotyledons, the plant will die. Look for a discolored hypocotyl (the “crook” of the soybean that first emerges from the ground), which indicates that damage occurred below the cotyledons.

Assessing your fields. It is best to assess damage to plants or seeds 48 to 96 hours after the drop in temperatures, as symptoms may take a few days to appear. Additionally, cold temperatures slow GDD accumulation and may further delay crop emergence. For corn, recent work suggests 50% emergence can be expected following accumulation of 130-170 soil GDDs (using soil temperature to calculate GDD rather than air temperatures) from planting, which may take 5-7 days to accumulate under normal weather conditions.