The Upper Iowa River completely flooded farm fields in Freeport Sunday evening, when the river reached its crest following a weekend of heavy rainfall. (Decorah Newspapers photo by Sarah Strandberg)
The Upper Iowa River completely flooded farm fields in Freeport Sunday evening, when the river reached its crest following a weekend of heavy rainfall. (Decorah Newspapers photo by Sarah Strandberg)
There are a number of key considerations which determine whether or not crops will withstand heavy flooding, according to ISU Agronomist Brian Lang.

"Survival depends on a number of factors," said Lang.

Lang said factors which determine the continued existence of a corn or soybean crop include the length of time a field is flooded, whether it is partially or completely submerged, temperature and stage of development.

"Basically, crops in flooded soils deplete available oxygen in 24 to 48 hours," said Lang.

Lang said the continued survival of crops is better with cool temperatures, cloudy days and clear nights.

"Of course, the quicker the water levels subside is most important. Partially submerged crops withstand water considerably longer than completely submerged plants," said Lang, adding disease problems may develop later in plants that survive a flood.

With regard to alfalfa, Lang said it can endure flooding for 14 days at a temperature of 60 degrees or 10 days at 70 degrees. It will last seven to eight days at 80 degrees and six days at 90 degrees.



Related factors

Lang said the effects of excess moisture are more severe after cutting, when there is little herbage to support it.

Flooded plants can also suffer from xylem necrosis (leaf death), beginning on the lowest stem, and phytophthora (root rot).

"If flooded or saturated soil conditions occurred prior to emergence, damping-off disease (which can kill or weaken seeds or seedlings before they germinate) is more likely to occur," said Lang.

He also said if silt from flooding is still attached to the plant when it is harvested, the forage will contain additional ash content resulting in a diminished feed quality.