Replanting Decisions in Corn and Soybeans… What to Consider

By Osler Ortez and Laura Lindsey et.al

Early plantings, cold air and soil temperatures, precipitation, wind, and warmer temperatures during or after planting may lead to reduced stands in planted fields due to factors such as imbibitional chilling, frost damage, soil crusting, and standing water. These factors (or combinations of them) can negatively affect seedling vigor, plant growth, crop establishment, and plant stands. Reduced stands may result in lower yields. If reduced stands are a concern, a potential solution is to replant fields. However, before replanting, here is a list of steps to consider:

Step 1. Wait… Plant stand should be assessed after ‘stable’ and ‘better’ conditions are achieved (e.g., warmer temperatures, good moisture conditions). Often, hasty decisions are not the best.

• For corn, past work has shown that 50% emergence can be expected following accumulation of 150 soil GDDs (base of 50°F) from the time of planting, about 5-7 days under normal conditions.
• For soybean, assess the stand at the VC growth stage. Visual stand assessment at the VE growth stage often underestimates the total number of plants that will emerge.

Step 2. Estimate the number of plants per acre from several areas within the field by conducting stand counts. Remember, field variability exists, and collecting stand counts from several representative areas is important (Figure 1).

Figure 1. In-field plant emergence variability in corn. Left and right plants with more growth and development relative to the plant in the center. 

• For corn, after estimating the number of plants per acre, use Table 1 to locate the expected yield of the plant stand depending on the planting date. Then, locate the expected replant yield by reading across from the expected replanting date to the stand that would be replanted. The difference between these numbers is the percentage yield change (increase or decrease) expected from replanting.

Table 1. University of Illinois Replant Chart Developed Under High Yielding Conditions (adapted from Nafziger, 1995-96).

• For soybean, replant is recommended only if the stand is less than 50,000 plants per acre. Although the stand will look poor, soybean plants can compensate for low plant populations by increasing the number of branches (Figure 2). In our research, going from 100,000 to 50,000 plants per acre resulted in only a 9 to 14% reduction in yield.

Figure 2. Soybean plants seeded at 100,000, 140,000, and 180,000 plants per acre.

Step 3. Check the weather forecast. How soon can you get back to the field to replant?

• For corn, early planting dates with lower stands can still produce good yields. From past research, a stand of 20,000 plants per acre planted on April 20 can still yield 91% of the optimum.
• For soybean, the date of planting has more effect on soybean grain yield than any other production practice. Yield loss resulting from delayed planting ranges from 0.25 to 1.0 bushel per acre per day. Replanting later may reduce yield more than having a low plant population.