Yield

Field Observations Thru September 8

Corn

Growth & Development

Most of the corn that I have seen this week is in either the R4 (Dough) or the R5 growth stage.

R5 – Dent

  • The second to last stage of corn development.
  • R5 (dent) occurs approximately 31‐33 days after silking.
  • Kernels are dented in at the top with the “milk line” separating the liquid and
    solid (starch) portions.
  • Within R5, kernels are often staged according to the progression of the milk line; i.e. ¼, ½, and ¾.
  • At the beginning of R5, kernels have 60% moisture content.
  • Stresses will reduce kernel weight at this time.

Scouting

I have heard a wide range for projected corn yields this year.  The Yield Component Method is the most widely used procedure for estimating corn yield.  While  you are out checking potential corn yields, also keep an eye out for:

  • Ear rots.
  • Stalk rots.
  • Anthracnose top dieback.
  • Stalk lodging.
  • Abnormal ear fill which identifies periods of stress.
  • Weed escapes (especially palmer & waterhemp).

Soybeans

Growth & Development

Soybeans are continuing to mature.  Last week I highlighted the R6 growth stage  the next stage is R7 the last growth stage prior to maturity.

R7 – Begining Maturity

  • One mature-colored pod anywhere on the main stem.
  • Yellow pods are moving toward maturity.
  • Tan, brown or tawny pods (depending on variety) signal physiological maturity.
  • Seeds at the R7 growth stage are at approximately 60% moisture.

Scouting

  • Foliar diseases – Sudden Death Syndrome, White Mold, and Frogeye Leaf Spot.
  • Insect feeding – Grasshoppers.
  • Weed escapes (especially Palmer and Waterhemp).

Estimating soybean yields

It is much more difficult to accurately predict soybean yield.  The process to estimate soybean yields can be found here.

County Rainfall Update

Estimating soybean yield

Soybeans are beginning to change color (mature) which has many of us thinking about yield potential.  To estimate soybean yield, four yield components need to be considered: plants per acre, pods per plant, seeds per pod, and seeds per pound (seed size).  A printable worksheet to estimate soybean yield can be found by clicking here.

Proceed with caution when estimating soybean yield. It is difficult to accurately predict soybean yield because of plant-to-plant variability and fall weather conditions can influence seed size.  Estimates are more accurate later in the growing season and on uniform stands.

To estimate soybean yield:

Step 1: To calculate plants per acre, count the number of pod-bearing plants in 1/1,000th of an acre.  In 7.5-inch row spacing, count the number of plants in 69 feet, 8 inches of row.  In 15-inch row spacing, count the number of plants in 34 feet, 10 inches of row.  In 30-inch row spacing, count the number of plants in 17 feet, 5 inches of row.

Step 2: To estimate pods per plant, count the number of pods (containing one or more seeds) from 10 plants selected at random.  Divide the total number of pods by 10 to get the average number of pods per plant.

Step 3: To estimate the number of seeds per pod, count the number of seeds from 10 pods selected at random.  Generally, the number of seeds per pod is 2.5, but this number can be less in stressful environmental conditions.  Divide the total number of seeds by 10 to get the average number of seeds per pod.

Step 4: To estimate the number of seeds per pound (seed size), assume that there are 3,000 seeds per pound.  If the soybean plants experienced stress, seed size will be reduced, and it will take more seeds to make one pound.  Use a seed size estimate of 3,500 seeds per pound if smaller seeds are expected because of late season stress.

Using the above estimates, the following formula can be used to estimate soybean yield in bushels per acre:  bushels per acre = [(plants/1,000th acre) x (pods/plant) x (seeds/pod)] ÷ [(seeds/pound) x 0.06]

 Example:110 plants per 1/1,000th acre, 65 pods per plant, 2.5 seeds per pod, 3,000 seeds per pound. [110 * 42 * 2.5] / [3,000 * 0.06] = 64.2 bushel per acre.

Estimating corn yields

According to the latest Ohio Crop Weather Report 90% of the Ohio corn crop is in the dough stage, 3 percentage points ahead of the 5-year average.  40% of the crop is in the dent stage 10% below the 5 year average.

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 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.  Assuming no stress during grain fill, 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.

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 32 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 (32 x 16 x 33) divided by 85, which equals 199 bu/acre.