3 Evaluating Crop Stand 

Corn plant populations are a critical component in achieving good yields. Often, because of poor weather, planter problems, insect damage, and other factors, growers obtain final stands far less than desired. Since this can lower yield, a careful evaluation is necessary to determine the actual population obtained. Additionally, some insect thresholds are influenced by the number of plants remaining.
Plant stands should be evaluated two to three weeks after plant emergence. Stands may be evaluated using either of two methods. Both methods involve stopping at randomly selected parts of the field and counting plants (that is, taking a sample). Table 2 recommends the number of samples to take, or stops to make, per field.

Method 1. Counting Plants per 10-Row-Feet Sample
At each stop, count the number of plants in an area measuring 10 feet along the row. Total the number of plants counted at all stops and divide by the number of stops. Using Table 3, look under the proper row width column and find the number that is closest to the average counted. Then find the corresponding plant population in Table 3.

Method 2. Counting Plants in a Length of Row Deter- mined by Row Width
Based on Table 1, make the appropriate number of stops per field. At each stop, measure a length of row as specified in Table 4 and count the plants within this area. Multiply the average number of plants counted (total counted divided by the number of stops) by 1,000 to obtain the final population per acre.
 

Table 2. Number of Samples per Field
No. Samples Field Size (acres)
3 1 to 15
5 16 to 30
7 31 to 50
A field larger than 50 acres should be broken into 2 units.
 
 

Table 3.  Estimating Crop Stand Using Method 1
 
Row Width  (Inches)
Population
28
30
36
38
40
 
(Number of Plants)
12,000
6.4
6.9
8.3
8.7
9.2
12,500
6.7
7.2
8.6
9.1
9.6
13,000
7.0
7.5
9.0
9.5
9.9
13,500
7.2
7.7
9.3
9.8
10.3
14,000
7.5
8.0
9.6
10.2
10.7
14,500
7.8
8.3
10.0
10.6
11.1
15,000
8.0
8.6
10.3
10.9
11.5
15,500
8.3
8.9
10.7
11.3
11.9
16,000
8.6
9.2
11.0
11.6
12.2
16,500
8.8
9.2
11.4
12.0
12.6
17,000
9.1
9.7
11.7
12.4
13.0
17,500
9.4
10.0
12.1
12.7
13.4
 
18,000
9.6
10.3
12.4
13.1
13.8
18,500
9.91
10.6
12.7
13.5
14.1
19,000
10.2
10.9
13.1
13.8
14.5
19,500
10.4
11.2
13.4
14.2
14.9
20,000
10.7
11.5
13.8
14.6
15.3
20,500
11.0
11.8
14.1
14.9
15.3
 
21,000
11.2
12.1
14.5
15.3
16.0
21,500
11.5
12.3
14.8
15.6
16.4
22,000
11.8
12.6
15.2
16.0
16.8
22,500
12.0
12.9
15.5
16.4
17.2
23,000
12.3
13.2
15.8
16.7
17.6
23,500
12.6
13.5
16.2
17.1
18.0
 
24,000
12.8
13.7
16.5
17.5
18.3
24,500
13.1
14.1
16.9
17.8
18.3
25,000
13.4
14.4
17.2
18.2
19.1
25,500
13.6
14.6
17.6
18.6
19.5
26,000
13.9
14.9
17.9
18.9
19.9
26,500
14.2
15.2
18.3
19.2
20.3
27,000
14.4
15.5
18.6
19.7
20.6
27,500
14.7
15.8
18.9
20.0
21.0
28,000
15.0
16.1
19.3
20.4
21.4
28,500
15.2
16.4
19.6
20.7
21.8
29,000
15.5
16.6
20.0
21.1
22.2
29,500
15.8
16.9
20.3
21.4
22.6
 
30,000
16.0
17.2
20.7
21.8
23.0
30,500
16.3
17.5
21.0
22.2
23.3
31,000
16.6
17.8
21.3
22.5
23.7
 

Table 4.  Length of Row To Be Counted
Row Width (Inches) Length of Row
28 18 ft., 8 in.
30 17 ft., 5 in.
36 14 ft., 6 in.
38 13 ft., 9 in.
40 13 ft., 1 in.
Example: In a 30-acre field with 36-inch rows, five stops are made and a section of the row 14 feet, 6 inches long is measured at each location. All plants within each 14-foot 6-inch area are counted. The counts from the five stops are added, then divided by five to get the average number of plants per stop. If the average is 20, multiply 20 by 1,000. The result is 20,000 plants per acre.

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