Frost, Wet Anaerobic Soils Affecting Seedling Establishment - UNL CropWatch, May 21, 2011

Frost, Wet Anaerobic Soils Affecting Seedling Establishment - UNL CropWatch, May 21, 2011

May 21, 2011

With the cool wet spring, serious concerns over seedling establishment are apparent. This past week, many producers saw what effect a late spring frost could have on their crops. This was especially apparent in low-lying areas.

Frost nipped many corn plants just emerging from the soil surface. Their coleoptiles (spike) along with the first leaf (plumule or embryonic – round tipped leaf) and some plants with the 1st true leaf (first pointed leaf) were subjected to a late killing frost. While some the leaf tissue appears to be frosted and brown (necrotic), know that the growing point of the corn plant does not come out of the ground until about the 4th to 6th true leaf stage, depending on variety. Thus the first several leaves can be safely sloughed off without long-term effects on crop establishment and/or subsequent yield.

Early Growth Process – Corn and Soybeans

At this time the growing point is well below the soil surface and the meristematic tissue is protected by the soil covering the plant. The intercalary meristematic tissue, as the term implies, pushes the developing leaf tissue out of the crop whorl, but the growing point stays well below the soil surface, initially.

If we compare the growing habit of corn to that of soybeans, we have an entirely different picture. Soybeans have an apical meristematic tissue growing point. This highly sensitive tissue is on the terminal ends of every stem and/or branch of the soybean plant. When it emerges, the growing point moves above ground and is subject to a killing frost. You freeze the apical meristematic tissue of a soybean plant, and it dies. You would have to replant, depending on the severity of the freeze (temperature low and duration of low). Farmers with soybeans that have already emerged, should check low-lying areas for confirmation of their survival.

Similarly, if emerging soybeans suffer injury (insect or mechanical) that breaks off the cotyledons (actual seed that has emerged and split into two equal parts), there will not be enough stored energy left for the plant to become established and survive. The cotyledons serve as a food source for the young soybean plant to become established.

After the root structure and subsequent leaf tissue develop, the cotyledons naturally fall off. That is why it may not be wise to rotary-hoe your soybeans (in surface crusting situations) for fear of breaking off the cotyledons. Even a crack in the hypocotyl will kill the plant. Timing of a rotary-hoeing is absolutely critical to survival. Similarly, if frost injures the cotyledons, survival of the soybean plant is unlikely.

How Anerobic Soils Affect Crop Growth

In addition to the frost, we have a lot of low-lying wet soils with poor drainage where plant development has been severely retarded. This is largely due to a lack of oxygen in the saturated soils. Soils without sufficient oxygen are said to be “anaerobic,” meaning “without oxygen.” Anaerobic soils occur where oxygen consumption by soil biota exceeds the diffusion of oxygen into the soil profile.

Low-lying areas of a wet field may have a musty smell. Remember the green leaf tissue of a corn or soybean plant trades oxygen and water molecules in exchange for carbon dioxide as they open their guard cells (stomates) in the outside skin covering (epidermis) of the leaves. The roots of a plant, however, still require oxygen for respiration. If you have too much water in these low-lying areas, not enough oxygen can enter those soils.

Poor aeration adversely affects crop growth in at least four ways:

  • growth of the plant, particularly the roots, is curtained;
  • absorption of nutrients decreases;
  • absorption of water decrease; and
  • the formation of certain inorganic compounds toxic to plant growth are favored.

In the case of wet fields, if possible, you will want to open up an area between the rows with a chisel shank or cultivator in an attempt to provide oxygen to the roots of your affected plants. This will encourage better crop growth and development.

Mark Hinze
Extension Educator, Hall County


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