Persistent rains during the past two weeks have resulted in ponding and saturated soils in many corn  fields and led to questions concerning what impact these conditions will have on corn performance. The extent to which ponding injures corn is determined by several factors including: plant stage of development when ponding occurs, duration of ponding and air/soil temperatures.
Corn is affected most by flooding at the early stages of growth. Once corn has reached the late vegetative stages, saturated soil conditions will usually not cause significant damage. Since most corn in Ohio is approaching the silking stage, this bodes well. Although standing water is evident in fields with compacted areas, ponding has usually been of limited duration, i.e. the water has drained off quickly within a few hours, so the injury resulting from the saturated soil conditions should be minimal. Moreover temperatures have been moderate.
However, under certain conditions saturated soils can result in yield losses. Although plants may not be killed outright by the oxygen deficiency and the carbon dioxide toxicity that result from saturated soils, root uptake of nutrients may be seriously reduced. Root growth and plant respiration slow down while root permeability to water and nutrient uptake decreases. Impaired nutrient uptake may result in deficiencies of nitrogen and other nutrients during the grain filling stage. Moreover, saturated soil conditions can also result in losses of nitrogen through denitrification and leaching.
Past research at Iowa State University evaluated flood damage to corn that was inundated for variable periods of time at different stages of growth (including silking). Two different nitrogen levels – "high" nitrogen (350 lbs. N/acre) vs. "low" nitrogen (50 lbs. N/acre) were also considered to determine how nitrogen affected corn response to flood injury. Low nitrogen plots yields were reduced by 16% at silking when plots were flooded for 96 and 72 hours. In the high-nitrogen plots, flooding at silking had little or no effect on yields.
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According to Dr. Emerson Nafziger at the University of Illinois , “…At the time the crop reaches stage V13 (about head-high), it still has to take up 110-120 lbs. of nitrogen, and in years when June is wet, a common question is whether or not the crop might run out of nitrogen, leaving the crop short.
“While the need for 20 or more lbs. of nitrogen per week would seem to raise the possibility of a shortage, the production of plant-available nitrogen from soil organic matter through the process of mineralization is also at its maximum rate in mid-season. For a crop with a good root system growing in a soil with 3 percent organic matter, mineralization at mid-season likely provides at least half the N needed by the crop on a daily basis. This means that normal amounts of fertilizer N, even if there has been some loss, should be adequate to supply the crop.”
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