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Dry Soils and Poor Corn Emergence (06/01/17)

Conditions during the last couple of weeks have been good for planting.

Dry Soils and Poor Corn Emergence

Conditions during the last couple of weeks ransom.1have been good for planting. Most of the corn and soybeans have now been planted (94 percent of the corn and 83 percent of the soybeans as of May 28). Plant stands in the early-planted corn fields I have seen in the eastern part of the state appear to be good to excellent. Nevertheless, I have heard of at least one case where corn emergence was extremely variable with the final plant population far below optimum. This was due to dry soil conditions coupled with a shallow planting depth. I suspect there will be more such reports in the coming weeks particularly for later planted fields as most of the state has not received adequate rainfall to restore moisture in the surface layer that was lost from tillage and evaporation. For most soils, 0.5 inches of rain (sandy soils slightly less) is needed in order for moisture to move to a 2 inch depth (the seed zone) in dry soils. Therefore, the 0.2 and 0.3 inch rainfall events received recently in parts of the state have not been sufficient to ensure good germination if the soil was previously dry. Other factors can also affect germination and emergence when soil moisture is marginal. Poor soil-seed contact can restrict the corn seed from extracting enough moisture from the soil to germinate. Crop residues that touch the seed can similarly impede the movement of water to the seed. Occasionally, fertilizers placed with the seed inhibit germination due to their salt effect being more pronounced in dry soils.

Moisture in the top two inches of soil is also required for nodal root development. Nodal roots develop from the crown, which establishes about ¾ inch below the soil’s surface, regardless of planting depth. These roots initiate soon after the V1 stage and rapidly develop to become the primary means by which the plant acquires water and nutrients by the V3 stage. If the soil remains dry around the crown for an extended period during early vegetative growth, however, nodal roots will not develop and when plants obtains sufficient size, they flop over (accompanying photo). Though this phenomenon, called the floppy or rootless corn syndrome is found occasionally in areas of the field with lighter soils or where there is compaction or shallow seeding, it may be more widespread during seasons of limited early rainfall like this year.

For those with poor stand struggling with a decision about replanting I have included a table developed from many years of experiments conducted in Wisconsin that may provide some guidance (Table 1). These data indicate that even a half stand planted early will likely be more productive than a full stand planted after the June 1st. Of course, uniformity of the field and uniformity of emergence can also be factors to consider when looking at the potential productivity of your field and the need for replanting. Before deciding to replant, also, take into account the final planting date for full insurance coverage for corn in your area (May 25 for all except the southeast corner which is May 31). When replanting, the original stand of corn should be destroyed before you replant. Late planted plants that grow next to an early-planted plant will be at a competitive disadvantage and will very likely not produce an ear.

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Information in this table is adapted from data obtained for the northern zone of Wisconsin (70-95 RM zone). See http://corn.agronomy.wisc.edu/Pubs/UWEX/A3353.pdf by J. Lauer for the full report. The May 1st column in this table assumes that a full season hybrid is used. All other columns assume a hybrid adapted to the shorter season is grown.

Joel Ransom

Extension Agronomist for Cereal Crops

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