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Calculating Yield
Wheat yields are a function of a combination of factors
- Plant population: which affects tillering and number of heads
- Head size: the number of spikelets per head
- Number of kernels per spikelet
- Size of the kernels.
- The amount of nitrogen available to the plant through Feekes stage 6 is critical to determining the number of tillers formed, unless water or some other factor becomes limiting. Feekes stage 6 is when the first
node of the stem becomes visible.
- The number of tillers that will form a head is determined by Feekes stage 6.
- The factors that affect head size are most significant from mid to late tillering, which corresponds with Feekes stage 3 for winter wheat (this occurs by the time the main stem has five or six leaves in spring
wheat).
- Number of kernels per spikelet is determined at late jointing - Feekes stages 5 to 6, while the maturing process occurs during the period between boot and early heading (stages 10 to 10.5).
- Management practices starting at stage 8 can have a significant effect on kernel size. The key is to keep the flag leaf healthy as long as possible and to provide enough water and nutrients for maximum grain
fill.
—Jim Bauder, Montana State University
extension soil and water quality specialist
Formulas for Estimating Wheat Yields
1) Bushels = (Heads) x (spikelets) x (2.3) (divided by row space) (per foot) (per head) (in inches) x 0.48 per acre
2) Bushels per acre of hard red spring wheat = kernels per head x heads in 3 ft x 0.0319
3) Bushels per acre of durum = kernels per head x heads in 3 ft x 0.0377
4) Bushels per acre of barley = kernels per head x heads in 3 ft x 0.0389
Formulas 2, 3, and 4 are for 7” row spacing and three foot of row (For 6” spacing, multiply final answers above by factor of 1.17)
Examples above are based on three foot row sample.
Estimating Corn Yield
There are several techniques for estimating corn grain yield prior to harvest. This version was developed by the Ag. Engineering Department at the University of Illinois and
is the one most commonly used. A numerical constant for kernel weight is figured into the equation in order to calculate grain yield. Since weight per kernel will vary depending on hybrid and environment, the yield
equation should only be used to estimate relative grain yield. For example, yield will be overestimated in a year with poor grain fill conditions, while it will be underestimated in a year with good grain fill
conditions.
Step1. Count the number of harvestable ears per 1/1000th acre. (See table below).
Step 2. Count the number of kernel rows per ear on every fifth ear. Calculate the average.
Step 3. Count the number of kernels per row on each of the same ears, but do not count kernels on either the butt or tip that are less than half size. Calculate the average.
Step 4. Yield (bushels per acre) equals:
(ear #) X (avg. row #) X(kernel #)
90
Estimated % corn grain yield loss due to defoliation at various growth stages1
|
|
% Leaf Defoliation
|
|
Growth Stage2
|
10
|
15
|
20
|
25
|
30
|
35
|
40
|
45
|
50
|
55
|
60
|
65
|
70
|
75
|
80
|
85
|
90
|
95
|
100
|
|
|
% Yield loss
|
|
7 leaf
|
0
|
0
|
0
|
0
|
0
|
0
|
1
|
1
|
2
|
3
|
4
|
4
|
5
|
5
|
6
|
7
|
8
|
9
|
9
|
|
8 leaf
|
0
|
0
|
0
|
0
|
0
|
1
|
1
|
2
|
3
|
4
|
5
|
5
|
6
|
6
|
7
|
8
|
9
|
10
|
11
|
|
9 leaf
|
0
|
0
|
0
|
1
|
1
|
2
|
2
|
3
|
4
|
5
|
6
|
6
|
7
|
7
|
9
|
10
|
11
|
12
|
13
|
|
10 leaf
|
0
|
0
|
0
|
1
|
2
|
3
|
4
|
5
|
6
|
7
|
8
|
8
|
9
|
9
|
11
|
13
|
14
|
15
|
16
|
|
11 leaf
|
0
|
0
|
1
|
1
|
2
|
3
|
5
|
6
|
7
|
8
|
9
|
10
|
11
|
12
|
14
|
16
|
18
|
20
|
22
|
|
12 leaf
|
0
|
0
|
1
|
2
|
3
|
4
|
5
|
7
|
9
|
10
|
11
|
13
|
15
|
16
|
18
|
20
|
23
|
26
|
28
|
|
13 leaf
|
0
|
1
|
1
|
2
|
3
|
4
|
6
|
8
|
10
|
11
|
13
|
15
|
17
|
19
|
22
|
25
|
28
|
31
|
34
|
|
14 leaf
|
0
|
1
|
2
|
3
|
4
|
6
|
8
|
10
|
13
|
15
|
17
|
20
|
22
|
25
|
28
|
32
|
36
|
40
|
44
|
|
15 leaf
|
1
|
1
|
2
|
3
|
5
|
7
|
9
|
12
|
15
|
17
|
20
|
23
|
26
|
30
|
34
|
38
|
42
|
46
|
51
|
|
16 leaf
|
1
|
2
|
3
|
4
|
6
|
8
|
11
|
14
|
18
|
20
|
23
|
27
|
31
|
36
|
40
|
44
|
49
|
55
|
61
|
|
17 leaf
|
2
|
3
|
4
|
5
|
7
|
9
|
13
|
17
|
21
|
24
|
28
|
32
|
37
|
43
|
48
|
53
|
59
|
65
|
72
|
|
18 leaf
|
2
|
3
|
5
|
7
|
9
|
11
|
15
|
19
|
24
|
28
|
33
|
38
|
44
|
50
|
56
|
62
|
69
|
76
|
84
|
|
19-21 leaf
|
3
|
4
|
6
|
8
|
11
|
14
|
18
|
22
|
27
|
32
|
38
|
43
|
51
|
57
|
64
|
71
|
79
|
87
|
96
|
|
Tassel
|
3
|
5
|
7
|
9
|
13
|
17
|
21
|
26
|
31
|
36
|
42
|
48
|
55
|
62
|
68
|
75
|
83
|
91
|
100
|
|
Silked
|
3
|
5
|
7
|
9
|
12
|
16
|
20
|
24
|
29
|
34
|
39
|
45
|
51
|
58
|
65
|
72
|
80
|
88
|
97
|
|
Silks brown
|
2
|
4
|
6
|
8
|
11
|
15
|
18
|
22
|
27
|
31
|
36
|
41
|
47
|
54
|
60
|
66
|
74
|
81
|
90
|
|
Pre-blister
|
2
|
3
|
5
|
7
|
10
|
13
|
16
|
20
|
24
|
28
|
32
|
37
|
43
|
49
|
54
|
60
|
66
|
73
|
81
|
|
Blister
|
2
|
3
|
5
|
7
|
10
|
13
|
16
|
19
|
22
|
26
|
30
|
34
|
39
|
45
|
50
|
55
|
60
|
66
|
73
|
|
Early milk
|
2
|
3
|
4
|
6
|
8
|
11
|
14
|
17
|
20
|
24
|
28
|
32
|
36
|
41
|
45
|
50
|
55
|
60
|
66
|
|
Milk
|
1
|
2
|
3
|
5
|
7
|
9
|
12
|
15
|
18
|
21
|
24
|
28
|
32
|
37
|
41
|
45
|
49
|
54
|
59
|
|
Late milk
|
1
|
2
|
3
|
4
|
6
|
8
|
10
|
12
|
15
|
18
|
21
|
24
|
28
|
32
|
35
|
38
|
42
|
46
|
50
|
|
Soft dough
|
1
|
1
|
2
|
2
|
4
|
6
|
8
|
10
|
12
|
14
|
17
|
20
|
23
|
26
|
29
|
32
|
35
|
38
|
41
|
|
Early dent
|
0
|
0
|
1
|
1
|
2
|
3
|
5
|
7
|
9
|
11
|
13
|
15
|
18
|
21
|
23
|
25
|
27
|
29
|
32
|
|
Dent
|
0
|
0
|
0
|
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