Winter wheat is one of the few crops that are in the ground and subject to the adverse effects of flooding. Reports indicate that many winter wheat fields have been flooded for varying periods this spring. Not surprisingly, there is considerable concern about the impact that flooding or waterlogging will have on the winter wheat crop.

Crop injury from waterlogging is primarily caused by the lack of oxygen. When soils become saturated, the amount of oxygen available to plant tissues below the surface of the soil (or water level during flooding) decreases as plants and microorganisms use up what is available. The movement of oxygen from the air into water/saturated soil is much slower than in well-aerated soil and much less than needed by the crop and other organisms in the soil.

“The depletion of oxygen rate in saturated soil is dependant on a number of factors, but temperature is the most important and predictable factor,” says Joel Ransom, North Dakota State University Extension Service agronomist for cereal crops. “The higher the temperature, the faster the rate of oxygen depletion. During summer conditions, the oxygen level in flooded/saturated soil reaches the point that is harmful to plant growth after 48 to 96 hours. Most research and observations suggest that plants submerged for more than five to seven days, when temperatures are greater than 65 degrees, will die and that yield can be impacted by flooding after as few as 48 hours.”

There is limited data on the effect of flooding on winter wheat when temperatures are below 40 degrees. Under cooler temperatures, the negative effects of flooding take longer to impact plant tissues, so producers can reasonably expect winter wheat to tolerate flooding beyond the limits described above for midsummer conditions.

“I did receive a report this week from someone in Canada, however, who found winter wheat surviving after being under water for three weeks,” Ransom says. “Winter wheat that has not broken dormancy may tolerate longer periods of submersion because dormant plants require less oxygen.”

Before writing off a winter wheat crop that has been flooded, Ransom suggests that producers confirm its viability by bringing a sample inside a warm building and observing it for regrowth after a couple of days.

Flooding can affect the subsequent growth and yield of a crop because of diseases, changes in soil fertility and damage to roots and growing points.

“For crops that survived the winter and the spring flooding, I think the prospects for normal development is quite good, provided there is adequate soil fertility for the developing plant,” Ransom says. “Excessive water can cause denitrification and leaching of nitrate nitrogen beyond the rooting zone of the developing plant, particularly in lighter-textured soils. Cool temperatures slow denitrification, so the leaching of nitrogen may be the biggest concern this spring. Some additional nitrogen may be needed in fields that have been flooded. To maximize yield response in winter wheat, the fertilizer should be applied well before jointing takes place.”

NDSU Agriculture Communication