CROP INSIGHTS
New Research Confirms Benefits of Improved Plant Spacing in Corn
by Tom Doerge, Tom Hall and Doug Gardner
Summary
 Past research has shown a benefit for improved within-row
plant spacing in corn fields, but results have not always been
consistent.
 Therefore, Pioneer researchers conducted new studies in
2001 and incorporated a new spatial analysis technique.
 Data from four diverse environments revealed an average
increase in grain yield of 3.4 bu/acre for every inch
improvement in plant spacing standard deviation.
 These results generally agreed with recent on-farm surveys
that showed a yield increase for improved plant spacing.
 Missing, misplaced and extra plants were found to have
different effects on yield. Poorly spaced and missing plants
decreased yield while occasional extra plants tended to
increase yields slightly.
 Future research is suggested to explain the mechanism of
plant response to spacing under various growing conditions.
“Picket fence” stands may increase yields with minimal input costs.
Summary of 2001 On-Farm Study
In 2001, Pioneer conducted an extensive on-farm plant spacing
study across four diverse corn-growing environments. The
objective of this study was to determine the effects of withinrow plant spacing on individual plant yield, using a new spatial
analysis technique.
Renewed Interest in Plant Spacing Uniformity
Methods
One way for corn growers to potentially increase yields with
minimal input costs is by improving within-row plant spacing
uniformity. This topic of “picket-fence” corn stands was
addressed frequently by extension agronomists and ag editors
in the early and mid-90s. Renewed interest in this concept has
occurred recently for at least two reasons:
Individual ear samples and within-row spacing measurements
were taken for over 6,000 plants from four commercial corn
fields in Missouri, Iowa (2) and Minnesota. Ear weights and
within-row measurements were used to calculate grain yields
of individual plants in bushels per acre. Spacial analysis was
then used to study the relationship between plant spacing and
grain yield per acre.
1. The popularity of several planter calibration services
currently being promoted across the Corn Belt, and
2. Testimonials of some corn yield contest winners who insist
that both adequate plant population and uniform spacing
are necessary for top yields.
New on-farm surveys across numerous growing environments
have clearly confirmed the benefits of improved within-row
plant spacing in increasing corn grain yield (Nielsen, 2001;
Doerge and Hall, 2000). However, a number of small-plot
university studies on plant spacing uniformity have given
inconsistent results (Lauer, 2001). These inconsistencies
suggest that additional research or a new methodology may be
needed to clarify this issue. Pioneer scientists have addressed
this problem by measuring thousands of individual plant yields
and developing a new spacial analysis tool to measure the
yield benefit of improved corn spacing.
CROP INSIGHTS
 VOL. 12  NO. 2  PAGE
Results
In the four fields included in the 2001 study, whole-field plant
spacing standard deviations ranged from 3.2 to 6.9 inches.
Improving the plant spacing standard deviation from its
original level down to zero (by using the new spatial analysis
technique) predicted grain yield increases of 7 to 19 bu/acre or
1.1 to 6.1 bu/acre/inch decrease in standard deviation. Across
all sites the average yield increase with improved plant spacing
was 3.4 bu/acre/inch.
The results of this study suggest that if the within-row plant
spacing standard deviation in a commercial field could be
improved by only one inch, the resulting yield benefit would
be about 3.4 bu/acre. In comparison, the yield increase needed
to offset the cost of planter meter calibration for a 600-acre
corn grower using a 12-row planter is only 0.5 bu/acre
(Doerge and Hall, 2000). Considering the amount of money a
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producer invests in their planter, seed, and other inputs, this
modest cost of planter meter calibration every 1 to 2 years is a
very inexpensive way to manage risk.
The remainder of this article provides a more complete
discussion of plant spacing uniformity, the methods used in the
2001 Pioneer study and the results obtained.
Sources of Plant Spacing Non-Uniformity
Within-row plant spacing standard deviation is a measure of
stand non-uniformity. This non-uniformity can arise from
several causes -- misplaced plants, missing plants (skips) and
extra plants (Figure 1).
Experimental Methods in 2001
Plant spacing measurements and individual ear sampling were
conducted in 2001 to determine the grain yield response per
acre for single plants. Individual plant measurements were
obtained in commercial fields at four contrasting locations
within the Corn Belt (Table 1).
Table 1. Location attributes of the four sites used in 2001 to
evaluate plant spacing effects on individual plant grain yield.
Location Hybrid CRM
Yield Level
(Bu/acre)
No. of Plants
Sampled
Missouri
34B28
109
102
884
Iowa 1
34B24
110
139
2,127
Iowa 2
33G30
112
162
1,560
Minnesota 35R58
105
193
1,450
Total
Figure 1. The three sources of plant spacing non-uniformity.
Researchers generally agree that increased plant spacing
standard deviation caused by missing plants will always result
in lower yields compared to a perfectly planted stand
(Nafziger, 1996).
There is less agreement on the effect of very closely-spaced
“extra” plants on overall yield. Some argue that crowding
will cause plants to go barren (produce no ear) as they
compete with each other for light, water and nutrients. Others
suggest that closely spaced plants will produce grain per unit
area that is at least equal to that of well-spaced plants
(Nafziger, 1996).
The effects of misplaced plants on yield is less apparent to
researchers. This study was conducted to help understand
those effects.
New Tool Needed for Plant Spacing Analysis
Previous studies have used plant spacing standard deviation as
the preferred index of spatial uniformity in corn fields.
However, this approach ignores that the three causes of higher
standard deviations may not all have the same effect on grain
yield and do not occur at the same proportions in each field. A
new analysis tool is needed for developing a better
understanding of the effects of misplaced, missing and extra
plants on grain yield.
6,021
The selected sites all exhibited a wide variation in plant
spacing uniformity. In addition, the locations covered a wide
range in growing season stresses, yield levels and hybrid
genetics. The hybrids used reflected three distinctly different
genetic backgrounds and varied in relative maturity (CRM)
from 105 to 112.
Three measurements were recorded for each plant; ear weight
and the distance to its two neighboring plants in the row. Row
width at all four locations was 30 inches. Measurements were
taken for all of the plants in paired 50-foot sections of row at
eight to twelve locations within these fields. Individual ears
were harvested, placed in paper bags and labeled as to their
location in the row. Ear samples from each location were
placed in plastic mesh bags, dried in a forced-air drier to a
constant moisture content below 15% and weighed.
Approximately 40 ears spanning the range of ear sizes
encountered at each of the four locations were selected. These
ears were hand shelled and the shelling percentages (% grain)
were determined. These values were used to calculate the
relationship between ear weight and grain weight for
individual plants from each of the four locations.
The field area assigned to each plant was calculated as
follows:
Within-row plant area = Within-row plant distance X Row width.
(Within-row plant distance is one-half the distance between a
plant’s two neighbors).
The individual plant grain yield per acre is then calculated as:
Individual plant yield (in bu/acre) =
Grain weight @ 15% moisture Within-row plant area.
CROP INSIGHTS
 VOL. 12  NO. 2  PAGE
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Figure 3. Plant spacing signature for the Iowa 2 location.
Results of Plant Spacing Analysis
Any analysis of plant spacing uniformity effects must consider
the proximity of both of a plant’s two neighbors. This is one of
the shortcomings of using the standard deviation of inter-plant
spacings as the single index of plant spacing uniformity. A
simple two-dimensional spatial analysis technique was
developed to overcome this limitation (Figure 2).
Distance to Neighbor A (inches)
Figure 2. Plant spacing analysis tool that depicts the
position of individual plants versus the distance to that
plant’s two within-row neighbors.
Distance to Neighbor B (inches)
25
Plant Spacing Signature
3
Skips
1
Skip
10
D
10
Ideal
5
0
5
10
15
20
25
Distance to Neighbor A (inches)
yield. Geographical Information System (GIS) software is used
to create these maps. Plant spacing yield maps are similar to
regular yield maps developed from yield monitor data. The
difference is that in plant spacing analysis, the coordinate
system is based on the distances to a plant’s two neighbors,
instead of latitude and longitude. Figure 4 shows the plant
spacing yield maps for the four locations studied in 2001.
4+ Skips
2
Skips
20
15
0
40
30
20
Ideal
The Effect of Within-Row Plant Area on Yield
Double
0
10
20
30
40
Triple Distance to Neighbor B (inches)
These maps provide two key findings concerning the effect of
within-row plant area on grain yield. One of these results was
expected, the other was not.
0
In a perfectly planted field with 30-inch rows and a population
of 29,840 plants/acre, the within-row distance between all
plants would be exactly 7.0 inches. If each plant were plotted
as a dot, all of the dots would fall on the same [7,7] point on
the graph. However, skips, doubles and triples inevitably occur
in all commercial corn fields. Figure 2 graphically shows the
different plant spacing outcomes that occur in commercial corn
fields.
Finally, the within-row distances to the two neighbors of
hundreds or even thousands of plants can be plotted on these
axes to give a visual representation of plant spacing uniformity
within a whole field. This can be thought of as the “plant
spacing signature” of that field.
Visual inspection of a plant spacing signature gives an
immediate indication of the quality of overall plant spacing
uniformity for a particular field. This is depicted in Figure 3
for the Iowa 2 location.
Yield Maps Based on Plant Spacing
This plant spacing analysis tool can also be used to create
yield contour maps that graphically show the effect of withinrow plant area and plant spacing uniformity on individual plant
CROP INSIGHTS
 VOL. 12  NO. 2  PAGE
As expected, individual plant yield on a per/acre basis
decreases continuously the farther it is positioned from the
origin [0,0]. This confirms previous research findings that
increases in plant spacing standard deviation due to “skips” or
missing plants always result in reduced overall yields
(Nafziger, 1996).
The remarkable finding at all four locations is that plants at
very close spacing (nearest the origin) are consistently the
highest yielding per acre. For these occasional closely-spaced
plants (comprising less than one percent of total plants in the
four fields studied), there was no evidence of increased
barrenness. These findings indicate that increases in plant
spacing standard deviation due to occasional closely-spaced
plants may actually improve overall grain yields.
The Effect of Plant Spacing Uniformity on Grain
Yield
These plant spacing yield maps also provide new information
on the effects of plant spacing uniformity at a constant plant
population. In Figure 4, plants falling on the solid diagonal
line connecting the [0,14] and the [14,0] points for the Iowa 1
location would all have the same within-row plant distance (7
inches), but would have quite different plant spacing
uniformity . This type of yield map can answer questions like
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Distance to Neighbor A (inches)
Figure 4. Plant spacing yield maps for the 2001 locations.
Missouri
30
Individual
Plant Yield
Bu/acre
Individual plant yield increased with improving plant spacing
uniformity, but only to a point. In general, individual plant
yield reached a maximum level when plants were within 2-3
inches of perfect equidistant spacing. This same pattern was
observed for all within-row plant distances and across all
locations.
200
180
160
20
140
120
10
100
80
These findings help explain why the relationship between
grain yield and whole-field plant spacing standard deviation is
not necessarily consistent from field to field. Plant spacing
standard deviation arising from missing, misplaced and extra
plants all have different effects on yield. Poorly spaced and
missing plants decrease yield while occasional extra plants, if
anything, increase yields slightly.
60
0
10
20
40
30
Distance to Neighbor A (inches)
Distance to Neighbor B (inches)
Iowa 1
20
Individual
Plant Yield
Bu/acre
200
16
12
180
• [0,14]
Benefits of Improved Plant Spacing Uniformity
160
140
[7,7]
•
8
Plant spacing yield maps can also be used to estimate the
potential benefits of improved plant spacing uniformity in
commercial corn fields. This is done by comparing the actual
yield measured at a location to the predicted yield if all of the
plants were at perfectly uniform spacing. These estimations are
summarized in Table 2 for the four locations used in this
study.
120
100
80
4
0
4
8
12
•
60
[14,0]
40
20
16
Distance to Neighbor B (inches)
Distance to Neighbor A (inches)
spacing, the expected yield is 143.4 bu/acre. At the [14,0]
point, spacing is at its worst, and the expected yield per plant
is 108.8 bu/acre.
20
Iowa 2
16
Improving the plant spacing standard deviation from its
original level down to zero improved yields by 7 to 19 bu/acre.
For these four sites, the change in yield per inch of
improvement in plant spacing standard deviation ranged from
1.1 to 6.1 with an average of 3.4 bu/acre/inch. This is very
similar to the findings of Nielsen’s (2001) extensive on-farm
survey in Indiana and Ohio.
Individual
Plant Yield
Bu/acre
200
180
160
12
140
120
8
100
Table 2. Estimated yield improvement due to improved plant
spacing at four on-farm locations in 2001.
80
4
60
0
4
8
12
16
20
40
Original Spacing
Distance to Neighbor A (inches)
Distance to Neighbor B (inches)
Minnesota
24
20
Perfect Spacing
Average
Spacing
S.D.
Yield
(Actual)
in.
in.
bu/acre
in.
bu/acre
bu/acre/in.
Missouri
10.8
6.9
102
0
109
1.1
160
Iowa 1
6.2
3.2
139
0
158
6.1
140
Iowa 2
7.1
3.6
163
0
174
2.9
Minnesota
7.1
3.8
193
0
206
3.3
Average
---
4.4
149
0
162
3.4
Individual
Plant Yield
Bu/acre
200
Yield ImYield
S.D. (Predicted) provement
180
16
12
120
8
100
80
4
60
0
4
8
12
16
20
24
40
Distance to Neighbor B (inches)
this one: “Do plants at perfect 7 X 7 inch spacing yield more
than plants at 14 X 0 inch spacing?”. At perfectly uniform
CROP INSIGHTS
 VOL. 12  NO. 2  PAGE
These results suggest that even if the aggregate plant spacing
standard deviation in a commercial field is improved by only
one inch, the resulting yield benefit would be about 3.4
bu/acre. The yield increase needed to just offset the cost of
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planter meter calibration for a 600-acre corn grower using a
12-row planter is only 0.5 bu/acre (Doerge and Hall, 2000).
Non-uniformity in corn stands places a grower’s sizable
investment in their planter, seed and other inputs at risk of
lower returns. Calibration of planter meters every 1-2 years is
an inexpensive way to help manage that risk.
Future Plant Spacing Research Needs
 What is/are the mechanism(s) for plant response to
spacing uniformity? (root, shoot, light interaction ?)
 Are there effects of different genetics or relative
maturities on response to plant spacing uniformity?
References
 What are the effects of plant spacing on yield
components?
Doerge, T.A. and T.E. Hall. 2000. The value of planter
calibration using the MeterMax* System. Pioneer Hi-Bred
International, Inc. Crop Insights Vol. 10, No. 23.
 Does response to plant spacing vary under rainfed vs
irrigated conditions?
Lauer, J.G. 2001. Theoretical and experimental evaluation of
within-row plant spacing in corn. Agron. Abstr. Amer. Soc.
Agron., Madison, WI.
Nafziger, E.D. 1996. Effects of missing and two-plant hills on
corn grain yield. J. Prod. Agric. 9:238-240.
Nielsen, R.L. 2001. Stand establishment variability in corn.
AGRY-91-1 (rev. Nov.-01), Department of Agronomy, Purdue
Univ., W. Lafayette, IN.
 Does plant spacing have a different effect at ultra-high
yield levels?
 Are there yield effects beyond the two nearest
neighboring plants?
 Are there plant spacing effects on seed production;
i.e. relative production of flats vs rounds, etc.?
 Are there plant spacing effects in crops other than
corn?
 How much yield variation is present, but unaccounted
for, in small plot research and on-farm strip tests due
to non-uniform plant spacing?
CROP INSIGHTS
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