Assessing soybean emergence

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Many factors can adversely affect soybean germination and emergence. Detecting and identifying emergence problems early will enable producers to make timely management decisions and implement management strategies as needed. Because of this, soybean producers should check emergence in each of their fields. Under ideal conditions, soybean emergence will occur in six days, but can take more than 15 days under more challenging conditions.

There are two methods for taking soybean emergence and stand counts:

  1. Counting the emerged seedlings in a length of row equal to 1/1,000 of an acre
  2. Counting emerged seedlings within a well-defined sampling area (Hula Hoop method)

The Hula Hoop method is recommended for a row spacing of 10 inches or less and the 1/1,000 of an acre method is recommended for the row spacing equaling or exceeding 14 inches.

Regardless of which method you use, take 10 random samples from different areas of each field and calculate the average. This will ensure that the sampled areas and your emergence counts represent the field. Only plants that have lifted their cotyledons out of the soil should be considered as emerged.

To use the information in Table 1 to estimate the number of soybean plants per acre in 30-inch rows, count the number of plants in 17 feet 5 inches of row at 10 random locations in the field. Simply multiply the average count for the 10 locations by 1,000 to get plants per acre. For example, if the average count in the sampled rows was 108, the population would be 108,000 emerged plants per acre.

To use the Hula Hoop method, toss the hoop in 10 random locations in the field and record the number of emerged plants within the hoop at each location. Calculate the average and multiply it by the appropriate conversion factor for the diameter of the hoop you are using. For example, if the diameter of the hoop is 30 inches and the average number of emerged plants is 16, the population is 143,984 emerged plants per acre (16 x 8,874). If the diameter of your hula hoop is not listed in Table 2, you can calculate the conversion factor with the following equation:
Conversion Factor = 43,560 ÷ [3.14 x (the inside hoop diameter in inches ÷ 2)2 ÷144]

If you count more than 100,000 plants per acre and the stand is relatively uniform, the field has the potential to produce high yields. If your emergence counts are lower than 100,000 plants per acre, you should determine the cause of the problem so that you can make informed and timely management decisions.

Table 1. Length of row required to equal 1/1,000 of an acre
Row Width Length of a single row to equal 1/1000 of an acre
15” 34 feet and 10 inches
20” 26 feet and 2 inches
22” 23 feet and 8 inches
28” 18 feet and 8 inches
30” 17 feet and 5 inches
Table 2. Converting hula hoop plant counts to plants per acre
Inside diameter of hula hoop Conversion Factor (multiply the number of plants within the hoop by the appropriate factor to calculate plants per acre)
36” 6,616
33” 7,334
30” 8,874

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