Jeff Rectenwald , CCA, Territory Agronomist for Asgrow/Dekalb
Now is a good time to be evaluating corn and soybean stands for plant populations, inter-row plant spacing, and seedling plant health. It takes about 100 growing degree units (GDU) before corn will emerge. While in the field, be on the lookout for black cutworms and bean leaf beetles.
When scouting fields, I like to take a piece of rope 17.4 inches long for determining corn plant populations, a hoop 28.2 inches in diameter for soybean populations, a tile spade for quickly digging plants out of the row, and a bucket with a lid and some water for washing off roots and looking for disease. These are just a few of the scouting tools that can be used for diagnostics in the field.
Evaluating plant emergence and viable plant population shortly after emergence is important for future management decisions. If population is greatly reduced, replanting may be justified and should be accomplished as soon as possible. Viable population may also influence decisions regarding weed control, irrigation, and grain marketing.
When evaluating a corn or soybean stand, only count plants that have a good chance of survival. Keep in mind that while corn plant populations are a critical component of yield, soybean plants are better able to compensate for low plant populations. Below are several methods that can be used to evaluate stands.
Count the number of plants in a length of row equal to 1/1000 of an acre based on row width. Multiply the number of plants by 1,000 to get plants per acre. Repeat the process in several locations in the field.
Stand count evaluation for 1/1000 acre based on row width and number of plants in a given row length.
Row Width (inches) Row length for 1/1000 acre
7 74-feet eight-inches
15 34-feet 10-inches
20 26-feet two-inches
30 17-feet five inches
A more accurate method is to count 150 plants and measure the distance from start to finish with a measuring wheel. Divide the number of feet traveled into the appropriate factor in Figure 2 to determine plant popula- tion. For example, if you walked 94 feet while counting 150 plants in 30 inch rows, the population is 2,613,600/94=27,804.
Stand count evaluation factors, by row width, for measuring the distance when counting 150 plants.
Row width (inches) Factor
This method is especially useful when determining stand counts in drilled soybeans. Measure the diameter of the hoop, toss it in the field and count the number of plants inside the hoop. Do this in at least 5 locations in the field. Multiply the average number of plants by the appropriate factor in to get the number of plants per acre.
Stand count evaluation factors, by hoop diameter, for determining soybean plant populations using the hoop method.
Diameter of hoop (inches) Factor