Introduction As you drive down the road in early summer, most corn fields appear uniform. However, a closer examination often reveals a wide variation in how evenly plants are spaced within the row. When planters are not operated or functioning properly, a high number of doubles or gaps may occur. Some researchers have suggested using standard deviation (SD) as a measure of in-row corn stand uniformity (Nielson, 1991). At Purdue University, Nielson (1991) has suggested that corn grain yield declines about 2.5 bu/acre for each 1 inch increase in standard deviation above a value of 2 inches. Conversely, many researchers have seen very little impact of corn spacing SD on final grain yield (Butzen, 1998). Nafziger (1996) has suggested that SD alone is not a good means of predicting yield responses to stand variability because of the differing and interactive effects of row skips, doubles, and plant density. Few studies have been done in the upper Midwest to quantify in-row stand uniformity of production corn fields and measure its effect on grain yield. To investigate this question, a research project was initiated in 1998. Methods Stand
uniformity in production fields Interactions
of planting speed, stand uniformity, and grain yield
|
|
Table
1.
Planter and field information for 1998 and 1999 corn stand
uniformity trials |
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|
Location |
Year
|
Planter
Make/model |
Seed
Delivery System |
Row
number/ |
Planting
Date |
Planting
Rate |
|
|
|
|
|
(#/in.) |
|
(seeds/acre) |
|
Lamartine |
1998 |
IH
Cyclo 800 |
air |
6/30 |
6
May |
32,000 |
|
Eden |
1998 |
JD
7000 |
finger |
6/30 |
21
May |
35,600 |
|
Malone |
1998 |
JD
7200 |
finger |
6/30 |
11
May |
30,900 |
|
Two
Rivers |
1998 |
JD
7200 |
air-vac |
6/30 |
14
May |
28,500 |
|
Mason |
1998 |
JD
1770 |
air-vac |
12/30 |
15
May |
30,000 |
|
Saxon |
1998 |
White
5400 |
air |
4/30 |
16
May |
26,000 |
|
Malone |
1999 |
JD
7200 |
finger |
6/30 |
11
May |
30,200 |
|
Byron |
1999 |
Kinze
2000 |
finger |
6/30 |
4
May |
31,000 |
|
Brownsville |
1999 |
JD
7200 |
finger |
6/30 |
2
May |
29,600 |
|
Gillett |
1999 |
JD
7000 |
finger |
6/30 |
13
May |
27,000 |
|
Saxon |
1999 |
White
5400 |
air |
4/30 |
28
May |
26,000 |
|
Arlington |
1999 |
Kinze
|
finger |
4/30 |
10
May |
30,000 |
Standard
Deviation Primer
SD
is a mathematical measure of variability within a group of measurements.
For example, a “perfect” corn stand with every plant exactly
the same distance away from the next plant would have a SD of 0 inches.
This of course never happens even with the best of planter
maintenance programs and operation.
The more variability that exists among plant-to-plant
measurements, the higher the SD value.
Effectively, SD describes how close all measurements cluster
around the sample average. Nielson
(1991) suggested that a SD of 2 inches is about the best a producer can
obtain in actual production fields because of planter performance
limitations and the fact that a small percentage of seed will not
germinate. A Survey of Stand Uniformity in Wisconsin Corn Fields
Eighty-seven Wisconsin corn fields have been evaluated for in-row
stand variation during the 1998 and 1999 growing seasons.
It is again important to emphasize that fields with good to
excellent emergence were targeted in an effort to measure corn planter
performance rather than other variables inhibiting germination and
emergence. Success in
accomplishing this goal is indicated by the fact that actual stands
averaged 97.1% of farmer-reported planting rates.
Corn planter characteristics and planting rates for these fields
are presented in Table 2. |
|
Table
2.
Overview of corn planters and planting rates for fields evaluated
(n=87) |
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|
Planter |
#
fields |
|
Row |
#
fields |
|
Target
Planting |
#
fields |
|
|
|||||||
|
|
|
|
(in) |
|
|
(seeds/acre) |
|
|
Finger |
57 |
|
20 |
2 |
|
<25,000 |
3 |
|
Air |
16 |
|
30 |
67 |
|
25,000
– 29,999 |
25 |
|
Vacuum |
9 |
|
36 |
8 |
|
30,000
– 35,000 |
58 |
|
Plate |
5 |
|
38 |
10 |
|
>35,000 |
1 |
| Average SD for all fields was 3.3 inches with a range of 1.9 to 5.9 (Table 3). Doubles per 50 ft. ranged from 0.1 to 25.9 with an average value of 5.1. Gaps per 50 ft. averaged 7.3 with a range of 1.0 to 16.9. Gaps had more of an impact and were a better predictor of SD than doubles (Figures 1 and 2). This is in agreement with previous research done by Nafziger (1996). Some fields with a relatively large number of doubles but few gaps still had very respectable SD values. This was especially (and perhaps not surprisingly) true of fields planted in 38-inch row spacings at relatively high plant densities. Conversely, the two fields planted in 20-inch rows had the lowest frequency of both gaps and doubles. Hence, it appears that SD alone is not a perfect indicator of stand uniformity by which to make comparisons unless other factors such as row spacing and plant density are similar. It was encouraging to note that most Wisconsin producers with fields in this study were planting seed at rates much higher than would have been the case ten years ago. Average planting rate for the 87 fields was 30,311 seeds per acre. Actual plant counts ranged from 22,264 to 35,501 plants per acre with an average of 29,377. |
|
Table
3.
Stand characteristics of 87 Wisconsin corn fields evaluated for
stand uniformity |
||
|
|
All-farm
Average |
All-farm
Range |
|
Standard
Deviation
(in) |
3.3 |
1.9
– 5.9 |
|
Doubles per 50 ft. of row |
5.1 |
0.1
– 25.9 |
|
Gaps per 50 ft. of row |
7.3 |
1.0
– 16.9 |
|
Average
spacing
(in) |
7.2 |
5.4
– 10.1 |
|
Planting
rate
(seeds/acre) |
30,311 |
21,000
– 35,600 |
|
Actual
plant density
(plts/acre) |
29,377 |
22,264
– 35,501 |
|
Stand as % of planted |
97.1% |
77.8%
- 113.5% |

| Figure 1. Relationship between row gaps per 50 ft. and standard deviation of in-row plant spacings in 87 Wisconsin corn fields. (1998-99) |

| Figure 1. Relationship between seed doubles per 50 ft. and standard deviation of in-row plant spacings in 87 Wisconsin corn fields. (1998-99) |
Planting speed, stand uniformity, and grain yield
We’ve determined that a large range of in-row plant-to-plant
stand variability exists in Wisconsin corn fields.
The next logical question is:
“Does this variability impact corn grain yield?”
Planting speed was used as a mechanism to force differences in
stand variability and measure the effects on grain yield with field
scale equipment. Nielson
(1995), in a series of on-farm strip trials conducted in Indiana, showed
that planting speed can have negative effects on stand uniformity. At the 5 locations where yield measurements were taken, yields tended to decline as planting speed increased (Figure 3). When averaged across all locations, a significant yield loss from 183 bu/acre at the 4 MPH planting speed to 176 bu/acre at the 8 MPH speed occurred (Figure 4). Along with this decline in grain yield, there was a significant increase in SD from 3.3 inches at 4 MPH to 4.2 inches at 8 MPH (Figure 4).
|

|
Because these fields had good initial emergence, and changes in plant population were not large enough to explain the yield reductions (Table 4), it can be assumed that yield declines were primarily attributed to differences in plant-to-plant spacing. A fair question to ask is why did we see a larger response in yield decline relative to increased SD (about 4% for a 1-inch increase in SD) than has been documented in other Midwestern states? Perhaps it is simply a function of the type of growing seasons we had. Both 1998 and 1999 were exceptional years in Wisconsin for growing corn. Another possible reason is that we may see more response to uniform stands in the northern states where growing seasons are shorter. Certainly it appears this is the case with narrowing corn row spacing to attain more equidistant plant spacing (Lauer, 1996). Small plot, replicated research is currently being conducted at the University of Wisconsin to evaluate a wider range of stand variability with different frequencies of doubles and row gaps. Until more data is collected, we will reserve further judgment other than it appears growers would be well served to strive for uniform stands. A
closer look at planting speed and stand variables
Stand uniformity data was collected on a total of 12 planting
speed trials during the 1998-99 growing seasons.
Of these, 7 were finger-type planters and 5 were air planters
(either positive or negative pressure).
Stand uniformity data for the 12 sites is presented in Table 4.
Although there were differences in results depending on location
and year, some trends are apparent.
It is important to note here that it is the trends that are
important rather than the performance of a specific planter make, model,
or type of seed delivery system. These
trials were done over a range of different field conditions, target
plant densities, and planter maintenance schedules. |
|
Table
4.
Effect of planting speed on stand uniformity variables at 12
Wisconsin locations (1998-99) |
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|
|
|
|
Stand
Variable |
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|
|
Planting Speed |
|
|
Plant |
Average |
|
|
|
Location
/ Year |
|
St.
Dev. |
Density |
Spacing |
Doubles |
Gaps |
|
|
|
|
|
(in) |
(plts/acre) |
(in) |
(per 50
ft.) |
(per 50
ft.) |
|
Malone -
98 |
4 MPH |
|
3.5 |
27,814 |
7.7 |
1.3 |
12.4 |
|
|
6 MPH |
|
3.5 |
28,524 |
7.5 |
3.2 |
9.5 |
|
|
8 MPH |
|
5.0 |
27,814 |
7.8 |
6.8 |
12.4 |
|
Eden - 98 |
4 MPH |
|
3.1 |
32,597 |
6.6 |
3.8 |
6.4 |
|
|
6 MPH |
|
4.0 |
34,049 |
6.3 |
16.7 |
7.7 |
|
|
8 MPH |
|
4.6 |
34,403 |
6.2 |
19.9 |
10.6 |
|
Lamartine
- 98* |
4 MPH |
|
4.1 |
28,902 |
7.6 |
7.7 |
12.2 |
|
|
6 MPH |
|
4.4 |
29,169 |
7.4 |
8.1 |
11.6 |
|
|
8 MPH |
|
5.4 |
27,298 |
8.0 |
11.5 |
16.8 |
|
Saxon -
98* |
4 MPH |
|
5.6 |
26,814 |
7.9 |
13.4 |
16.4 |
|
|
6 MPH |
|
6.2 |
27,007 |
7.8 |
16.3 |
17.8 |
|
|
8 MPH |
|
7.4 |
25,262 |
8.5 |
15.3 |
21.5 |
|
Two Rivers
- 98* |
4 MPH |
|
3.5 |
28,911 |
7.4 |
4.3 |
8.7 |
|
|
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