Managing Thin Soybean Stands

Mike Staton, MSU Extension Soybean Educator

Thin soybean stands can occur for a variety of reasons such as disease and insect damage, dry soil, a poor seedbed, or planting equipment failures or maladjustments. Producers need to know if remedial action is warranted and what specific action steps to take.

The most important step is to detect emergence problems and identify potentially thin stands as early as possible. The next step is to identify what caused the poor emergence. This is important as it determines if the problem needs to be addressed and what needs to be done. Uneven or slow emergence due to variable planting depth, crusting or dry soil may not require any action if rain is forecast. However, if rain is not predicted, rotary hoeing may be required to break up a soil crust. If poor stands occur even though adequate soil moisture has been available and soil temperatures are above 50°F, dig up seed and look for signs of normal germination (swollen seed and root or shoot growth). Also, look for diseased tissue or signs of insect feeding.

Estimating your existing and potential stand is the next step. There are two accepted ways for estimating stands - counting plants in a defined area such as a hula hoop and counting plants in a length of row equal to 1/1000 of an acre. Both work well, but I prefer the 1/1000 of an acre method for wider row widths.

Table 1. Length of Row Required to Equal 1/1,000 of an Acre

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. Then, 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