PUTNAM COUNTY — Rainfall this weekend helped some drought stressed
corn fields. The U.S. Drought Monitor estimates 46 percent of Ohio was
rated “moderate drought” in northern Ohio and 15 percent in “severe
drought”. Two procedures to estimate corn grain yields prior to harvest
are the YIELD COMPONENT METHOD and the EAR WEIGHT METHOD. Each method
will produce yield estimates that are within 20 bu/ac of actual yield.
YIELD COMPONENT METHOD principle advantage is that it can be used at
the milk stage of kernel development, currently similar to most Ohio
corn fields. The yield component method uses a numerical constant
sometimes referred to as a “fudgefactor” 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.
For the YIELD COMPONENT
METHOD, Dr. Bob Nielsen at Purdue University suggests a “fudge factor”
of 80 to 85 (85,000 kernels per 56 lb bushel) as a realistic value to
use in the yield estimation equations. Dr. Emerson Nafziger at the
University of Illinois says under current drought stress “…. If there’s a
fair amount of green leaf area and kernels have already reached dough
stage, using 90 [as the “fudge-factor “] might be reasonable. If green
leaf area is mostly gone and kernels look like they may be starting to
shrink a little, kernels may end up very light, and using 120 or even
140 [as the “fudge-factor”] might be more accurate”.
estimated grain yield as follows: 1) Count the number of harvestable
ears in a length of row equivalent to 1/1000th acre or 17 ft. 5 in. for
30 inch rows. 2) On every fifth ear, count the number of kernel rows per
ear and determine the average. 3) 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.)
4) Yield (bushels per acre) equals (ear #) x (avg. row #) x (avg.
kernel #) divided by 90. 5) Repeat the procedure for at least four
Example: You are evaluating a field with 30 inch
rows. You counted 24 ears (per 17’ 5” row section). Every fifth ear
resulted in an average row number of 16 and an average number of kernels
per row of 30. The estimated yield for that site in the field would be
(24 x 16 x 30) divided by 90, which equals 128 bu/acre.
WEIGHT METHOD can only be used after the grain is physiologically mature
(black layer), which occurs at about 3035 percent grain moisture.
Sample several sites in the field and measure off a length of row equal
to 1/1000th acre. Count the number of harvestable ears in the 1/1000th
acre. Weigh every fifth ear and calculate the average ear weight
(pounds) for the site. Hand shell the same ears, mix the grain well, and
determine average percent grain moisture.
grain yield as follows: A) Multiply ear number by average ear weight. B)
Multiply average grain moisture by 1.411. C) Add 46.2 to the result
from step B. D) Divide the result from step A by the result from step C.
E) Multiply the result from step D by 1,000.
Example: You are
evaluating a field with 30 inch rows. You counted 24 ears (per 17 ft. 5
in. section). Sampling every fifth ear resulted in an average ear weight
of 1/2 pound. The average grain moisture was 30 percent. Estimated
yield would be [(24 x 0.5) / ((1.411 x 30) + 46.2)] x 1,000, which
equals 135 bu/acre.
Because it can be used at a relatively early
stage of kernel development, the Yield Component Method may be of
greater assistance to farmers trying to make a decision about whether to
harvest their corn for grain or silage because there is greater benefit
in harvesting fields with marginal corn grain yield potential for
silage. From Dr. Peter Thomison OSU Corn Specialist, CORN Newsletter
Note: This is my last news article since I have taken
a new job as NRCS Soil Health Specialist for Ohio and Southern
Michigan, located in Findlay. Thanks for the opportunity to serve
agriculture in Putnam County.