As heavy rainfall has been trendy in 2022, crops have taken the hit. When there's an excess of rain, crops are susceptible to flooding and waterlogged soils, resulting in immersion of plants.
Water standing in a corn field, V5 stage, on June 8, 2022. Franklin County, Ohio.
For corn, waterlogged crops at the V4-V16 growth stages restrict yield potential when reducing ear size, and the amount of kern rows per ear. Yield loss in corn can also be affected by Nitrogen (N) application. Corn waterlogged at the V4-V5 growth stage for 3-4 days reduced yield in Ohio trials by 25-45% when 100-120 lb N were applied pre-plant and no additional nitrogen was applied compared to non-flooded plots. On the plots that had pre-plant N applied, adding 60-120 lb N post-flooding resulted in yield losses of only 3-15% compared to non-flooded controls receiving the same N application regime. Nitrogen loss (or lack of uptake) at the time of flooding can result in greater yield loss compared to fields with adequate nitrogen; waterlogging for 3 days with 120 or 180 lb N applied entirely after flooding had 28 or 9% lower yield compared to non-flooded plants receiving the same N program. The later the flooding occurs in corn, the less impact it has on grain yield losses. Bacteria deposited in leaf whorls by flooding may also result in diseases and dead plants.
Disease problems of greater risk due to ponding include corn smut, pythium and crazy top. If plants are covered with mud due to the excess water, photosynthesis may be limited but it is unlikely that the photosynthetic capacity of leaves has been completely destroyed. Smaller amounts of rain can wash silt off leaves allowing for resumption of photosynthesis. It will also help wash mud out of leaf whorls allowing new leaves to emerge. Wet soil conditions may also increase susceptibility to root lodging of larger plants (approaching the V10 stage or later). For corn that's emerged, check the color of the growing point to assess plant survival after flooding. It should be white to cream-colored, while a darkening and/or softening usually precedes plant death.
For corn not yet emerged, evaluate the appearance and integrity of seeds or seedlings that have yet to emerge (likely rotting if discolored and softening.) Also check for soil crusting as the soil dries, and be prepared to use a rotary hoe in the event crusting is impending emergence. Look for new leaf growth 3 to 5 days after water drains from the field.
Water standing in a soybean field. Symptoms of flood stress/saturated soils include yellow stunted plants.
Soybeans tend to be more sensitive to flooding stress during the reproductive stages rather than during the vegetative stages. Flooding for up to 4 days may not impact seed yield if it occurs during the vegetative (V4-V5) stages. A flood duration of 7 days or more can decrease yield by 17% to 63% in soybeans if it occurs during the vegetative stages. However, a flood duration of 4 days or greater during reproductive stages (R2-R5) can result in significant yield loss (25% to 85%.) Additionally, there is a wide range in varietal tolerance to flooding for soybeans, so every variety may not be impacted the same.
A greater concern may be the incidence of oomycete infection for young soybean plants, and producers may be on the lookout for phytophthora stem and root rot later in the season. If seed treatments were employed before planting, this could help minimize those issues. At the vegetative stage, symptoms of flood stress (saturated soil) include yellow stunted plants and poor root growth and nodulation.
Besides corn and soybean, forages can also be impacted by heavy rainfall events. The degree of injury is dependent on species, environmental factors and when crop was last harvested. Alfalfa is particularly sensitive to waterlogging injury, especially under high light conditions. Damage from flooding can be most severe if it occurs shortly after cutting. Harvesting alfalfa 2 and 12 days before soil flooding reduced regrowth yield by 56% and 33%, respectively.
Unharvested plants were not injured with a flooding duration of up to 14 days. Be aware of these interactions and allow extra recovery time if alfalfa is waterlogged soon after cutting. Waterlogged fields should also be protected from potato leafhopper injury to avoid permanent crown damage and stand loss that will plague you for the remaining life of the stand. Severely damaged alfalfa stands can be no-till interseeded with sudangrass to increase forage yield this year.
Growers should learn the impacts excess water may contain, such as direct yield and from an economic standpoint. Furthermore, they should develop a plan and be prepared for future damage.
Alfalfa field showing poor drainage between tile lines, Auglaise County, Ohio 2019.