Estimating Soybean Stands with a Cell Phone App

By Daniela Carrijo

The time for stand counts is near!

As of May 12, 2024, about 20% of the expected soybean acres in Pennsylvania have been planted (USDA, NASS, Crop Progress Report). That means the time is near for assessing the plantings and performing stand counts. The earliest time you can go out and get an accurate stand count estimate in soybeans is at the VC stage (unifoliate leaves are fully expanded, Figure 1). Performing stand counts at the VE stage (i.e., emergence, cotyledons are above the surface) will likely result in an underestimation of plant population. This is especially true when soybean emergence tends to be less uniform, for example, in drill-seeded soybeans and slopy fields in which variations in seed depth placement and soil moisture can be large.

The traditional method for performing stand counts in soybeans is to count the number of plants for a given area in different parts of the field and extrapolate plant counts to an acre basis. Step-by-step instructions are described in this previous article. However, if you have a smartphone or tablet, you can use the Bean Cam App to do most of the counting. Bean Cam is a free app developed by the University of Wisconsin that is available for download on Android and iOS devices. It is mostly useful for soybean row spacings of 7.5, 15, and 30 inches, so the instructions below are only valid for these soybean row spacings.

Using the Bean Cam App

1. Go to the App Store on your device and search for “Bean Cam.” Download the app.
2. Type the name of the field where you will perform stand counts and click “Create.”
3. Select the soybean growth stage and row spacing representative of the field. Then, select “use camera” as the counting method. Note that this counting method is only available for 7.5-, 15-, and 30-inch row spacings.
4. Go to one of five spots in the field that are representative of the entire field or field area where you would like to get the stand count estimate.
5. Measure an area that is five feet wide by four feet in row length. Five feet wide equates to two rows in 30-inch soybeans, four rows in 15-inch soybeans, and eight rows in 7.5-inch soybeans. Count the total number of plants in this 5x4-foot area.
6. Click on “Sample 1” and take a picture of the same area you counted in step 5. When taking the picture, place the camera directly above the soybean rows so the camera is parallel to the ground, and line up the soybean rows with the yellow lines on the screen. A contrast filter can be toggled off and on to help you see the rows on the screen.
7. After taking the picture, the App will show the number of plants counted. Compare this number with the manual count from step 5 and move the calibration slider until both numbers match. Now, the App is calibrated, and you can move on to the remaining four field locations.
8. Move on to the second, third, fourth, and fifth field locations (samples 2, 3, 4, and 5, respectively) and take a picture of the soybean stand as you did in step 6. You do not need to manually count these.
9. Once five pictures are taken, the App will calculate the average plant population of the field.

Considerations when Using the App

While this App does a great job at counting soybean plants, there are a few considerations that still require the human eye. First, the App does not measure the uniformity of plant distribution within a row. So, it is possible that even though the field average indicates a satisfactory stand count, some areas may justify filling in because of large gaps within the rows. Second, if there are many emerged plants that are significantly damaged (e.g., missing leaves and/or growing point), it is important to make sure that the standard estimate reflects only plants that will likely make it through harvest. Manual stand counts may be needed in these situations.

Replanting Decisions

A suboptimal stand count at VC is not an automatic replant. In addition to stand counts, deciding whether or not to replant will depend on several factors, such as:

• The distribution of plants and their ability to recover are not accounted for by the Bean Cam App, as mentioned above.
• Replanting costs and seed availability.
• Changes in weed management may be warranted. For example, a suboptimal stand will result in lower canopy cover, which may require more aggressive weed management. Conversely, replanted fields will have plants at different growth stages, which may limit herbicide options.
• The tradeoff between plant population and planting date. This is probably the most important consideration because there is a significant penalty for delayed planting. Therefore, by the time an accurate stand assessment can be made, the yield penalty caused by a poor stand could be equal to or less than that of an optimal stand planted later (i.e., replanted). Tables 1.6-3 and 1.6-5 of the Penn State Agronomy Guide depict this tradeoff. For example, in 30-inch soybeans, a field planted on May 10 with a suboptimal plant population of 40,000 plants per acre has the same yield potential (88% of full yield potential) as a field planted on June 10 with an optimal plant population of 120,000 plants/acre.

Final Two Cents

While suboptimal stands trigger thoughts of desperation in most of us, soybean plants are great at compensating for open spaces, and most research shows that replanting soybeans is rarely economical. If possible, repair the plant (“fill in” an existing stand) instead of starting over.