Flooded Fields

Jun 17, 2015
By Russel Higgins
Storm fronts dropping up to 5 inches of rain have swept across northern Illinois with additional rain in the forecast. The question asked by many farmers as they scout saturated fields from the truck is "how long" can crops in standing water survive? Flooding reduces yields by decreasing stands, and slowing dry matter accumulation or both. The most obvious effect of flooding is the lack of oxygen for the roots. Research has shown that oxygen concentration can be close to zero after 24 hours in flooded soil. Without oxygen, the plant can't perform important functions like respiration, critical for plant growth. Still, predicting the survivability of crops in saturated soils is challenging and highly variable.
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The majority of recent storms are tracking from west to east, hitting Iowa first. Brian Lang,  ISU Extension Agronomist shared the following tips in his June 15th Crop notes.
Flooding or Prolonged Saturated Soils on Corn
• Flooding before V6 is more damaging than later.
• Completely submerged plants are at higher risk for damage than those partially submerged.
• The longer flooding persists, plant damage and death increases.
• Soil temperature affects how quickly plants are damaged by flooding. Seedlings can survive up to 4 days of flooding when temperatures are relatively cool (mid-60°F or cooler) but fewer days if temperatures are warm (mid-70°F or warmer).
• Flooding damages roots, making plants more susceptible to stresses later in the season.
• Substantial amounts of nitrogen can be lost from flooded soils due to denitrification and nitrate leaching.
• Flooding or wet soils favor the development of seed decay and seedling blights as well as crazy top.
• As flood water subsides, mud deposits on plants can reduce photosynthesis. Ironically, rainfall is helpful to wash off the mud.
Several issues that most farmers had hoped would be solved by a week a above average temperatures has been delayed by rain and overcast conditions. 
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