Pennsylvania Soybeans: Early-Season Stand Assessment

No-till soybeans in crop residue. Photo: Iowa State University

As soybean fields begin to emerge, you may notice some variable stands. Now can be a perfect time to examine those fields and make management decisions on whether to fill in a stand, replant, or leave them alone.

One of the first key factors that must be assessed is the stand density. There are two basic ways to calculate stand: Counting linear plants in a row, or the “hula hoop” method.

Counting plants

First, determine your row spacing. Here are some common row spacings, and the appropriate length of row needed for 1/1,000th of an acre:

Row Width (inches) Length of Row Needed to
Represent 1/1,000th of an Acre
30 17 feet, 5 inches
20 26 feet, 2 inches
15 34 feet, 10 inches
10 52 feet, 3 inches
7.5 69 feet, 7 inches

Adapted from Purdue Corn & Soybean Field Guide

Take at least five counts from different areas of the field, calculate the average, and then multiply by 1,000 to get the population per acre.

Hula-Hoop method

Any round hoop will work, but hula hoops can be a very cost-effective option that may already be present somewhere on the farmstead. Measure the diameter of the hoop, and use the table below to calculate the plant population:

Diameter of Hoop (inches) Factor to Multiply to get
Number of Plants Per Acre
18 24,662
21 18,119
24 13,872
27 10,961
30 8,878
33 7,337
36 6,165

Adapted from Purdue Corn & Soybean Field Guide

Take at least five randomly selected locations within the field, average the number of plants, and multiply by the factor to calculate plants per acre.

Based on the stand count, the next step would be to estimate the yield potential of the field. One of the most remarkable aspects of a soybean plant is the ability to compensate for missing plants. The table below compares yield potential for different populations:

Population Drill (7.5” rows) Planter (30” rows)
160,000 100% 100%
120,000 100% 100%
80,000 96% 100%
60,000 92% 94%
40,000 87% 88%
20,000 77% 81%
10,000 58% 72%

Adapted from Purdue Corn & Soybean Field Guide

If a decision to replant is made, there are several different factors to consider. First is the yield potential for a delayed planting date. According to the Penn State Agronomy Guide Table 1.6-5, a field planted on June 10 will only have 88% of the yield potential for the same field which would have been planted on May 10. That figure drops to 76% of potential yield on June 20. You also must consider the costs of seed, fuel, machinery and other expenses.

For more information on stand assessment, including a worksheet on replanting decisions, check out this factsheet produced by Purdue Extension or this Making Soybean Replant Decisions article by Penn State Extension.

You can also watch a YouTube video of Dr. Shaun Casteel, Purdue Extension Soybean Specialist, demonstrate a stand assessment in soybeans using both the hula hoop and the linear methods:

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