Determining yield potential for a problematic stand
It seems that almost every spring there is discussion about replant issues to some degree. Several environmental scenarios will increase the possibility of needing to replant, including prolonged cold soils, freezing temperatures, excessively wet soils, and insect feeding.
Two scenarios typically exist in fields with problematic stands:
- The corn had non-uniform emergence resulting in different plant developmental stages. It is highly unlikely that you will benefit from replanting a field that appears this way. In general, a two-leaf differential between plants can reduce yields 5-10% because the smaller plants compete with the larger plants. Estimate yield loss in fields exhibiting non-uniform development (see the article Tools to calculate yield loss from uneven heights).
- The corn has a significantly lower population than desired. Replanting may be beneficial in this case. Several considerations and comparisons should be made when determining if a specific field fits this category.
Measure the existing plant population in several random areas in the field; this will help determine the potential yield of the field. Go to the Replant Checklist for information on the steps needed to evaluate an existing stand in a problem field.
The most important factor in deciding whether or not replanting will be beneficial is to calculate your expected yield now versus what you could potentially have if it was replanted. Refer to Figure 1 inserted here as a reference. Data contained here shows relative yield potential for numerous planting dates and plant populations.
| Planting Date | ||||||
|---|---|---|---|---|---|---|
| April 20-May 5 | May 13-19 | May 26-June 1 | June 10-16 | June 24-28 | ||
| Final Stand* | Relative Yield Potential (%) | |||||
| 28,000-32,000 | 100 | 99 | 90 | 68 | 52 | |
| 24,000 | 94 | 93 | 85 | 64 | 49 | |
| 20,000 | 81 | 80 | 73 | 55 | 42 | |
| 16,000 | 74 | 73 | 67 | 50 | 38 | |
| 12,000 | 68 | 67 | 61 | 46 | 35 | |
Figure 1. Influence of planting date and plant population on corn grain yields. (Based on current research, this table potentially overestimates corn yields with later planting dates.) Source: Iowa State University Extension, 2001. Corn Planting Guide , PM 1885, (Table 7). *Assumes uniform plant spacing
Let's consider that a producer wants to replant late-May. The field was originally planted on April 26 but only has a population of 24,000 plants per acre. Is there any yield advantage to replanting it now? By looking at the May 26-June 1 planting date window in the table, we can estimate the relative yield potential expected from a later planting. Approximately 90 percent of the maximum yield potential would be achieved if it was replanted at a final population of 32,000 plants per acre. Yet the producer's existing stand of 24,000 plants/acre will reach approximately 94 percent of its yield potential; therefore, it is better to leave the original stand than to replant. Realize that extra costs will occur from replanting not only upfront but also potentially post-harvest due to higher grain moisture content.
In Corn planting dates, we discussed ISU current planting date research (2006) that showed a positive yield response to earlier planting dates. Based on preliminary data it appears that producers can plant prior to April 20th and attain 100% yield, if conditions are favorable. In Table 7 of the Corn Planting Guide, 99-100% relative yield potential is shown to occur with planting dates between April 20 and May 19. It is possible that the values given in the table are more optimistic than what they should be particularly for mid-late May plantings.
Of course, numerous factors will determine what each field may potentially yield; data can only be used as a tool in approximating what may result. Producers should take the values contained within the table as approximate values, realizing that the actual yield loss may be greater or less than what is shown for a particular year.
Portions of text, written by Lori Abendroth and Roger Elmore, originally appeared in the Integrated Crop Management extension newsletter on pages 133-134 of the IC-496(12) - May 22, 2006 issue.
