Source: Alexander Lindsey, Peter Thomison
Persistent rains during May and early June 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). Under certain conditions, saturated soils can result in yield losses. Saturated soil conditions can result in losses of nitrogen through denitrification and leaching. Additionally, root uptake of nutrients may be seriously reduced even if plants are not killed outright by the oxygen deficiency and the carbon dioxide toxicity that result from saturated soil conditions. 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. Once the corn has reached the late vegetative stages, saturated soil conditions will usually not cause significant damage. Moreover, moderate temperatures should help minimize the level of stress.
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). In Ohio in 2017-2018, we observed a 10% yield loss when corn was flooded at V4 for 2 days and received 120 lbs N pre-plant + 60 lbs N sidedress (applied post-flood). When flooded for 4 or 6 days, yield loss increased to 15 and 33%, respectively, when receiving the same N regime. If the additional 60 lbs N was not side-dressed post-flood, yield losses increased to 30, 50, or 57% for 2, 4, or 6 days of flooding, respectively. 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.”
If the rain has been paired with strong winds, root lodging may occur. Yield losses of 4, 10, and 15-25% have been reported for 100% root lodging at V10, V13-15, and V17-R1, respectively in Wisconsin. Results from Ohio in 2018 suggest these values may be greater than previously reported (8, 37, and 58% yield loss when root-lodged at V10, V13-14, and VT-R1, respectively). This trial will be repeated in 2019 in Ohio.
Disease problems that become greater risks due to ponding and cool temperatures include Pythium, corn smut, and crazy top. Fungicide seed treatments will help reduce stand loss, but the duration of protection is limited to about two weeks. The fungus that causes crazy top depends on saturated soil conditions to infect corn seedlings. There is limited hybrid resistance to these diseases and predicting damage from corn smut and crazy top is difficult until later in the growing season. However, the economic impact of these latter two diseases is usually negligible.