Estimating Yields

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.

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 Soybean Yields Prior to Harvest
Yield estimates made prior to maturity can be done by counting yield components rather than weighing using the following procedure, from Edward Oplinger, extension agronomist, University of Wisconsin-Madison.

1. Count the number of pod-bearing plants in 1/1,000 acre. (For 7-inch rows count plants in 75 ft of row, 15-inch rows count 35 ft and 30-inch count 17.5 ft of row.)
2. Determine pods/plant by counting number of pods (containing one or more seeds) from 10 plants selected at random. Divide total pod number by 10 to get pods/plant.
3. Calculate the estimated yield using the formula: (# plants) x (pods per plant) ÷ 60 = bu/acre.

Example: If the number of pod-bearing plants in 1/1,000 acre was 120 and the average number of pods per plant was 25, the estimated yield would be: 120 x 25 ÷ 60 = 50 bu/acre.

Repeating steps in several places in the field will improve the accuracy of the yield estimate.

If the number of beans/pod and/or the number of beans/pound are known or are measured, then instead of step 3 use this formula:

(# plants) x (pods per plant) x (beans per pod) ÷ (# beans per lb) x (.06) = bu/acre.

Example: If the number of pod-bearing plants in 1/1,000 acre was 120, the number of pods per plant was 25, the beans/pod was 2.5 and there were 2,200 seeds/lb, the estimated yield would be (120 x 25 x 2.5) ÷ (2,200 x .06) = 56.81 bu/acre.

Estimating Sunflower Yield

To estimate crop yield, you need to take the following into account:

• Plant population
• Head diameter
• Seed size category
• Good seed set
• Center seed set

The following web site explains how to estimate these factors: www.ag.ndsu.nodak.edu/aginfo/procrop/sun/yildes08.htm.

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.

Step 1. 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