Watch wet wheat
University of Missouri agronomist Greg Luce warns that flooding, ice sheeting and generally waterlogged soils could have a significant impact on wheat crops across the MFA trade territory.
“As with most weather-related events, the level of impact will need to be judged on a field-by-field basis, yet there are some important factors to keep in mind,” said Luce, an adjunct instructor at MU and Research Director for the Missouri Soybean Association.
Crop injury from waterlogging and ice sheeting is primarily caused by the lack of oxygen. A main concern of the flooding is the impact on the growing point of wheat which is below ground until after tillering. The growing point is subject to water saturation or ice cover and the amount of oxygen available to plant tissues below the surface of the soil decreases as plants and microorganisms use up what is available. The depletion of oxygen in saturated soil is dependent on many factors, but temperature is an important factor.
At higher temperatures, the rate of oxygen depletion is greater. For example, during summer conditions, the oxygen level in water saturated soil reaches the point that is harmful to plant growth after 48 to 96 hours. However, under cooler temperatures, the negative effects of flooding take longer to impact plant tissues. Dormancy of wheat, or cover crops like cereal rye, greatly reduces the requirement for oxygen but does not eliminate it. According to Luce, warm temperatures in December meant winter crops were not dormant when the wet weather began.
“Considering the extreme conditions, it seems reasonable that some stand loss is expected in the areas where water saturation or ice sheeting remains for long periods. However, before writing off a winter wheat crop that has been flooded, or ice covered, experience has taught me that wheat is very resilient,” Luce reported through an MU Integrated Pest Management bulletin. “I would suggest that growers confirm wheat viability by bringing a sample inside a warm building and observing it for regrowth after a couple of days,” he said.
“This could be done later in the winter, prior to green-up. If, after exhibiting new leaf growth, the plants also sprout new white roots, a grower can be relatively assured that the sampled area holds some live plants. If the plant is in good condition, the crown will appear white and healthy, and new roots will be developing. At green-up, field scale decisions will need to be made,” explained Luce.
The critical threshold for a wheat grain field is an average of 12 to 15 live plants per square foot.
Also consider nitrogen loss, said Luce.
“Excessive water can cause denitrification and leaching of nitrate nitrogen beyond the rooting zone of the developing plant, particularly in lighter-textured soils. Soil temperatures below 50º F slow the nitrification and denitrification processes, so loss of nitrogen at this point may not be significant. Also, most nitrogen tends to be applied to wheat in the spring anyway.”
Luce said to maximize yield response in winter wheat, the majority of nitrogen fertilizer should be applied before jointing takes place.
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