Flooding Impacts on Corn Growth & Development

The first few months of 2019 were very moist in Iowa, with near-record snowfall totals during the winter months followed by a wetter-than-average spring. The result of the excess moisture was flooding across the state, which hit historic levels in some regions. This flooding impacted Iowa’s agricultural sector in a big way, both during and after the waters had receded. This article will address the impacts of flooding on corn production, a key component of agriculture in Iowa & the Midwest.

EFFECT ON THE PLANT

When a corn crop is submerged in water, its oxygen supply is greatly reduced. The oxygen supply to the plant approaches zero after 48 hours, which greatly reduces or even stops critical plant functions such as nutrient and water uptake^1,2. Submerged corn also experiences a reduction in photosynthesis rates³. Expect some damage to corn that has been submerged for a certain length of time, but this damage should be minimal if the flooding duration was less than 48 hours^1,2,3.  Once the flooding duration gets to 4 days, the survival chances for the corn are greatly reduced^1,2,3. For longer-term flooding, corn has a greater survival chance if temperatures are not too warm (60’s, low 70’s) and it has established growth above the water surface^1,2,3. Fully submerged seedlings (no growth above water level) will likely not survive after 4 days². See Table 1 for potential damages and survival chances for flooded corn at different growth stages.

Table 1. Survival of flooded corn plants. Adapted from Crop Watch Newsletter (University of Nebraska), 20 May 2005.

Soils that have been flooded are also susceptible to injury, which can impact corn production long after the flood waters have receded. When fields are flooded for an extended period of time, a significant amount of nitrogen loss can be expected. Research out of the University of Nebraska found that at 55-60ᵒF, soils flooded for 5 days lose 10% of the total nitrogen applied to the field. This number jumps up to 75% at temperatures of 75-80ᵒF². Along with nutrient loss, flooded soils can also develop a hard, crusty layer on the surface once waters have receded. This can inhibit seedling emergence and reduce the amount of water and oxygen supply to the roots^1,2.

MANAGEMENT OPTIONS

It is recommended to wait about five days after flood waters recede before assessing the damage done to the corn crop. Pull up a few plants and examine the growing point. If the growing point is cream-colored, the corn can recover with minimal impact to yield if favorable growing conditions are present during the rest of the season^2,3. However, if the growing point is soft and darkened, it is dying^2,3. A decision to replant should be made only after assessing stands and considering the economics of replanting or converting the acreage to soybean or another crop. An Iowa State University Extension resource on determining when to replant is the Corn Planting Guide (PM 1885). Corn planted prior to May 15 would be expected to yield similarly to the corn that was already planted if stands are comparable and diseases do not infect the seed or seedling. Therefore, if stands are extremely poor, replanting would be a good option; although, be aware that conditions can quickly change with several good days of weather. Only consider reapplying nitrogen to fields if soil nitrate concentrations are below 20 ppm¹. For crusting on soil surfaces, cultivating between rows or using a rotary hoe should be done as soon as possible to allow water and oxygen to get to the roots, or allowing new seedling to emerge^1,2.

SOURCES

[1] Holmberg, M, 2019. Effects of Flooding on Corn. Online: http://www.agrigold.com/Universal/Articles/Effects-of-Flooding-on-Corn/.

[2] Rea Hybrids, 2019. Effects of Flooding on Corn Emergence. Online: https://www.rea-hybrids.com/en-us/agronomy-library/effects-of-flooding-on-corn-emergence.html.

[3] Heisler, M, n.d. Between the Rows: Effects of Flooding and Saturated Soils on Corn. Online: https://www.wyffels.com/uploads/attachments/BTR_Effects_of_Flooded_and_Saturated_Fields_on_Corn.pdf.