By Peter Thomison and Alexander Lindsey, Ohio State University Extension
Persistent rains during the past two weeks have resulted in ponding and saturated soils in many Ohio 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: (1) plant stage of development when ponding occurs, (2) duration of ponding and (3) air/soil temperatures. Corn is affected most by flooding at the early stages of growth (see https://agcrops.osu.edu/newsletter/corn-newsletter/2018-15/young-corn-wet-feet-what-can-we-expect). 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 late vegetative stages, 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). Past work has indicated <10% yield loss when corn was flooded for 2 days or less. Moreover, temperatures have been moderate which will minimize the level of stress. If the rain has been paired with strong winds, root lodging may occur. Yield losses of 4, 10, and 15-25% reported for 100% root lodging at V10, V13-15, and V17-R1, respectively in Wisconsin. These values are currently being re-evaluated for Ohio by OSU researchers.
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 N levels (“high” N ‑ 350 lb N/ac vs. “low” N‑50 lb N/ac) were also considered to determine how N affected corn response to flood injury. Corn that was flooded when 30” tall (approximately V6) experienced a 6-8% reduction under high N, and a 15-30% yield reduction under low N. Low N plots yields were reduced by 16% at silking when plots were flooded for 96 and 72 hours. In the high N plots, flooding at silking had little or no effect on yields.
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.
According to Dr. Emerson Nafziger at the University of Illinois (http://bulletin.ipm.illinois.edu/?p=1240) “…At the time the crop reaches stage V13 (about head-high), it still has to take up 110 to 120 lb of N, 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 lb of N per week would seem to raise the possibility of a shortage, the production of plant-available N 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.”