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Corn and Soybean Replant Decisions

William Wiebold
Extension Professor
Division of Plant Sciences
Raymond Massey
Extension Professor
Department of Agricultural and Applied Economics and Commercial Agriculture Program

Deciding whether to replant a sparse stand is one of the more difficult decisions a corn or soybean grower will face. The difficulty of this decision stems from the difficulty of predicting how the effectiveness of replanting will be affected by the combination of planting date and changing environmental conditions. However difficult, replant decisions are made by at least some Missouri farmers every year.

This guide provides a step-by-step procedure for estimating dollar gain or loss from replanting. This procedure involves a careful study of the field in question and an analysis of its yield potential. Follow these steps:

  • Determine the cause of the sparse stand.
  • Determine the stand density and condition of the stand.
  • Determine the yield potential of the sparse stand.
  • Estimate the expected gross revenue from the sparse stand.
  • Estimate the cost to replant.
  • Estimate the yield potential and gross revenue from a replanted stand.
  • Determine whether replanting will pay for itself.

Cause of the sparse stand

Accurate determination of the cause of the sparse stand is an essential first step because a sparse stand can also result when replanting unless the cause is identified and corrected. Causes of sparse stands before emergence include poor seed quality, improper seeding practices, low moisture availability, soil crusting, saturated soil, herbicide injury, insect feeding and disease infection. Stand density can be reduced after emergence by weather events, diseases or animal feeding. Replanting should be contemplated only if the cause for the sparse stand can be corrected.

In most instances, planting into existing sparse stands is not recommended because stands with a mixture of plant sizes and maturities perform poorly. This is particularly true with corn. You can remove existing stands with either herbicides or tillage. Replanting without tillage saves time and soil moisture without diluting existing preemergence herbicides.

Stand density and condition

An accurate estimate of the remaining live plant population is necessary to determine potential yield of the sparse stand. If possible, wait several days to determine if plants are alive or regrowth is possible. The number of areas to be sampled depends on the uniformity of the damaged stand. With nearly uniform damage, fewer areas need to be sampled. Always remember that some portions of the field may not need to be replanted. Count the number of live plants in the appropriate areas, and calculate stand. As you count plants, you must decide if the plant is healthy or at least capable of recovery. Do not count weak plants or plants damaged beyond reasonable potential for recovery. To estimate stands after hail or animal damage, note which parts of the plant are damaged and how they affect the potential for regrowth. Leaf removal, for example, is far less serious than bruising of the lower stem.

Be sure to note the condition of the remaining plants and the field, including the extent of plant defoliation, the presence of large gaps in stands and the amount of weed pressure.

Count plants in an area for which you know the dimensions so that you can calculate the number of plants per acre. You can simplify your calculation by counting plants in a length of row equal to one-thousandth of an acre and multiplying by 1,000. Table 1 provides the row lengths equivalent to one-thousandth of an acre for 15- , 20- and 30-inch wide rows For drilled soybean, use the hula hoop method and refer to Table 2.

Table 1. Row length that equals one-thousandth of an acre.

Row width Row length that equals 1/1000 acre
30 inches 17 feet, 5 inches
20 inches 26 feet, 2 inches
15 inches 34 feet, 10 inches

Table 2. Hula hoop method for estimating population of drilled soybean.

Number of plants in hoop Inside diameter of hoop (inches)
30 32 34 36 38
Thousands of plants per acre
2 18 15 14 12 11
4 35 31 28 25 22
6 53 47 41 37 33
8 71 62 55 49 44
10 89 78 69 62 55
12 107 94 83 74 66
14 124 109 97 86 77
16 142 125 110 99 89
To perform the hula hoop method, randomly toss a hoop onto the field. Count the number of plants inside the hoop. Then use this table to determine the number of plants per acre: In the first column, find the number of plants in the hoop. Follow the row across to the column for the hoop’s diameter. The number indicated is in thousands. For example, if 12 plants are inside a 34-inch hoop, the field contains about 83,000 plants.

Yield potential of the stand

Yield is greatly influenced by both environment and genetics. Corn and soybean yields are most affected by weather conditions in July and August, respectively. As it is nearly impossible to predict in May or early June what weather events will occur in July or August, assume normal weather patterns unless you have good reason to believe differently.

Use Tables 3 and 4 to estimate yield potential. Data in Tables 3 and 4 are expressed as a percentage of “expected yield” under normal conditions. You or your crop adviser must determine this expected yield. Neither overestimate nor underestimate expected yields for the location and soil type in question. An accurate estimate is essential to a proper replant recommendation.

Table 3. Estimated corn yield potential at various plant populations (yield as percent of expected).

Population Yield environment
Normal High*
Percent of expected yield
36,000   100
34,000   99
32,000   98
30,000 100 96
28,000 99 93
26,000 98 90
24,000 95 87
22,000 92 82
20,000 88 77
18,000 83 72
16,000 78 67
14,000 73 62
12,000 68 57
*High-yield environments consistently produce yields of more than 190 bushels per acre. Soils are deep with excellent water-holding capacity. Irrigation is common.

Table 4. Estimated soybean yield potential at various plant populations (yield as percent of normal).

Population Row width (inches)
30 7
Percent of expected yield
120,000 100 100
110,000 99 98
100,000 98 96
90,000 97 94
80,000 95 92
70,000 92 89
60,000 87 85
50,000 81 79
40,000 73 71
30,000 60 58
20,000 46 43

Expected gross revenue of the sparse stand

The decision to replant will be based on what you expect the grain to be worth at harvest. Current market price will probably not be the market price at harvest. Use a market advisory service or the futures market (less local basis) to estimate the price at harvest time.

The predicted market price can greatly influence replant decisions, so make an honest prediction. Determine income by multiplying predicted yield by the predicted market price.

Cost of replanting

Even if yield from replanting would be greater than that from the damaged field, the cost of replanting may still exceed the value of the additional yield from replanting. Therefore, you must estimate as accurately as possible the following costs.

Seed cost: Determine cost of seed by multiplying unit cost by the seeding rate. In many instances, seed companies reduce seed prices if their products were initially used in the sparse stands.

Fuel, machinery and labor costs: Include all fuel and machinery costs associated with replanting. Reduced tillage or no-till methods will reduce these costs. Custom charges for planting or chemical application can be used but may overstate the cost of replanting if you use your own equipment.

Pesticide costs: Usually additional preemergence herbicide will not be necessary unless tillage is performed. If you do not use tillage to remove the existing stand, a burndown herbicide application is necessary. Include only those costs that would not be incurred from already-planned herbicide applications. If the sparse stand resulted from disease or insect damage, additional fungicide or insecticide may be needed.

Additional costs: These costs would include interest on loans associated with replanting, increased dryer costs for late maturing corn, and labor costs not already covered.

For purposes of this analysis, none of the other costs of production are important. Fertilizer, chemical and other costs already incurred in production are considered sunk costs that do not affect the decision to replant. These costs affect profitability, but the replant decision addresses only the question of whether the increased revenue from replanting exceeds the increased cost associated with replanting.

Likely yield and income from replanted field

Delayed planting will usually decrease yield potential. The amount of decrease is difficult to predict. Use Tables 5 and 6 to estimate the effect of planting date on yield from replanted fields.

Once yield is predicted, determine income by multiplying yield by the predicted market price. Use the same predicted market price that you used in estimating expected gross revenue of the sparse stand. Estimate net income by subtracting the cost of replanting from expected income.

Table 5. Effect of planting date on corn and soybean yield in central and north Missouri.

Corn Soybean
Planting date Yield as percent of expected Planting date Yield as percent of expected
May 1 94 May 8 99
May 6 92 May15 98
May 11 89 May 22 96
May 16 86 May 29 93
May 21 83 June 5 89
May 26 80 June 12 84
May 31 77 June 19 79
June 5 75 June 26 72
June 10 71 July 3 65
June 15 65 July 10 54

Table 6. Effect of planting date on corn and soybean yield in southeast and southwest Missouri.

Corn Soybean
Planting date Yield as percent of expected Planting date Yield as percent of expected
April 1 99 May 8 100
April 6 98 May 15 99
April 11 96 May 22 98
April 16 94 May 29 96
April 21 91 June 5 93
April 26 88 June 12 89
May 1 85 June 19 84
May 6 82 June 26 79
May 11 79 July 3 72
May 16 75 July 10 65
May 21 70    
May 26 65    

Making the decision

To determine whether replanting is appropriate, compare the net income from replanting with the income from a sparse stand. Even if this comparison is positive, you still may not wish to replant. Other demands on your time and competing crop management issues are important considerations.

The worksheet on the following page can help in organizing the important information and arriving at a well-informed decision. It is followed by an example of a completed worksheet with a note about the probable decision.

An automated Microsoft Excel workbook that helps with the replant decision is available at http://agebb.missouri.edu/download/university/replant.xlsx.

Corn/soybean replant worksheet

A. Estimated stand density of sparse stand plants/acre
B. “Expected” yield in bushels/acre bu/acre
C. Effect of sparse stand on yield potential (from Table 3 or 4) percent
D. Estimated yield from sparse stand
(line B × line C ÷ 100)
bu/acre
E. Estimated market value of crop $/bushel
F. Estimated income from sparse stand
(line E × line D)
$/acre
G. Extra herbicide needed due to sparse stand $/acre
H. Expected net income from sparse stand line F − line G) $/acre
I. Estimated cost to replant
(total of lines 1 + 2 + 3 + 4 below)
1. Seed __________
2. Fuel, machinery, labor________
3. Pesticides __________
4. Additional costs __________
$/acre
J. Effect of planting date on yield (from Table 5 or 6) percent
K. Estimated yield from replanted stand (line B × line J ÷ 100) bu/acre
L. Estimated income from replanted stand(line E × line K) $/acre
M. Net income from replanted stand (line L − line I) $/acre
N. Profit or loss from replanting (line M − line H) $/acre
Note
Sparse stands may also result in some additional expenses. Defoliated plants and sparse stands may require an additional herbicide application.

Corn/soybean replant worksheet example*

A. Estimated stand density of sparse stand 14,000 plants/acre
B. “Expected” yield in bushels/acre 165 bu/acre
C. Effect of sparse stand on yield potential (from Table 3 or 4) 73 percent
D. Estimated yield from sparse stand (line B × line C ÷ 100) 120.45 bu/acre
E. Estimated market value of crop $5.50 /bushel
F. Estimated income from sparse stand (line E × line D) $662.48 /acre
G. Extra herbicide needed due to sparse stand $10.00 /acre
H. Expected net income from sparse stand (line F − line G) $652.48 /acre
I. Estimated cost to replant (total of lines 1 + 2 + 3 + 4 below)
1. Seed __________
2. Fuel, machinery, labor________
3. Pesticides __________
4. Additional costs __________
$50.00 /acre
J. Effect of planting date on yield (from Table 5 or 6) 83 percent
K. Estimated yield from replanted stand (line B × line J ÷ 100) 136.95 bu/acre
L. Estimated income from replanted stand (line E × line K) $753.23 /acre
M. Net income from replanted stand(line L − line I) $703.23 /acre
N. Profit or loss from replanting (line M − line H) $50.75 /acre
*Assumptions
 
  1. Corn planted in central Missouri.
  2. Original planting date was April 28.
  3. Earliest replanting date is May 21.
Note
In this example, the grower would probably replant corn if it did not interfere with soybean planting or some other activity. However, if wet soil conditions were present so that replanting was delayed until May 31, it may not pay to replant.

 


G4091 Corn and Soybean Replant Decisions | University of Missouri Extension