While your city cousins are comparing the depth of water in their basements, you are frantically trying to dig drainage channels between your fields and the nearest ditch. With multiple inches of rain on wet fields, ponding has increased, and there are now large gaps in fields with small beans. Excess moisture in many parts of the Cornbelt has created great concerns for how long the crop can survive with wet feet. Let’s address some of your questions about flooded fields.

Soybeans can survive more than 48 hours underwater, but the actual length of time depends on the temperature, cloud cover, the soil moisture prior to flooding and the rate the pond drains. Wisconsin agronomist Shawn Conley says high temperature and sunshine speeds up plant respiration and that depletes oxygen. “If the soil was already saturated prior to flooding, soybean death will occur more quickly as slow soil drainage after flooding will prevent gas exchange between the rhizosphere and the air above the soil surface. Soybeans often do not fully recover from flooding injury.” And water logging can cut yields 17 to 43%. Conley says consult your crop insurance agent before you replant.

The rate of field drying after a flooding event also plays a large role in soybean survival, says Minnesota agronomist Seth Naeve. Also, researchers have found yield reductions to be much greater on flooded clay soils than on silt loam soils when flooded for the same period of time (Scott et al, 1989). At the V4 stage, these researchers reported yield losses of 1.8 bu/ac per day of flooding on a clay soil and 0.8 bu/ac per day on a silt loam soil.

If replanting is a possibility, Michigan State agronomist Kurt Thelen says soybeans can generally be planted up to the end of June although yields will likely be reduced commensurate with the later planting date. If replanting soybeans, do not drop more than one maturity group from what you usually plant. For example, if you generally plant group II soybeans, replant with group II or group I soybeans.

When replanting flooded out areas that still have some viable plants, it is usually best to tear up the existing stand and start over with an even-emerging stand. This may require you to manage the area differently than the non-flooded parts of the field with regard to activities based on plant growth stage such as weed control and time of harvest. Other considerations in flooded out areas include potential weed problems from weed seed brought in by encroaching waters, herbicide residue washed in from adjacent fields, loss of herbicide control from excessive leaching or erosion, and increased incidence of phytophthora and other root disease. Nodule function in soybeans is also reduced in saturated soil. However, nodule activity resumes to normal levels once the soil dries out.

Yield loss increases rapidly every day planting is delayed after May 15, says Iowa State soybean agronomist Palle Pedersen. Most of our current planting date information is based on planting conducted from late April to early June; therefore we do not have any new information on the yield penalty if the planting is done in late June and early July. When soybean planting is delayed, vegetative growth is reduced since flowering can start as soon as the plants have one or two nodes. Thus, soybean planted later does not develop the same canopy biomass as soybean of the same variety planted earlier. Late-planted soybeans are therefore shorter. The time from flowering to harvest maturity is generally the same when a variety is planted at different planting dates since it is controlled by the maturity group for that specific variety. Changing to an earlier maturing variety is not necessary unless the planting and/or replanting date is very late.

If your corn has failed because of flooding, can you plant soybeans in it? That depends on the herbicides used for your corn, say Purdue agronomists Bill Johnson and Glenn Nice. The only herbicides labeled for use in corn which would allow replanting soybean immediately are Prowl and Python. All other soil-applied corn herbicides have a several month rotational interval which must elapse before soybean can be planted. Most of the post emergence herbicides have shorter rotational intervals, but would still require a couple of weeks before soybean can be planted.

An increasing number of farmers paying high cash rents have been using crop insurance, and if that is one of your options for revenue management, Iowa State ag economist William Edwards says crop insurance may help with either replanting or prevented planting, since there is still nearly 10% of the expected soybean acreage that has yet to be planted. Prevented planting acres must have a cover crop sown on them, and must be reported to the appropriate insurance agent by June 28 (corn) or July 13 (soybeans). An acreage report on all insured acres must still be submitted to the agent by June 30.

In addition, acres that produce below average yields in the fall could still qualify for an indemnity payment under the normal yield or revenue insurance guarantees. Coverage levels are gradually reduced for corn acres planted after May 31 and soybean acres planted after June 15, so it is important for producers to record the number of acres planted on each date.

If these issues do not answer all of your questions, visit the resources assembled by Purdue agronomist Bob Nielsen.

When flooding hits in mid-June, problems extend from prevented planting to replanting and delayed planting, and each has its own set of problems. As seen with wet weather in 2009, delayed crop maturity from late planting created many additional problems. While most crops were planted on time this year, flooding has created may replant enigmas for both beans and corn. The calendar is not too late for planting or replanting soybeans, but some fields may be able to survive with only spot planting in ponds.

Source: Stu Ellis, University of Illinois