Corn tilted or “disk”. Photo: Ohio State University
Excessive drying of the upper soil profile contributes to the development of what some of us kindly call the syndrome of “rootless corn” or “loose corn”. The problem illustrates a classic example of the importance of stress times depending on the stage of plant development.
The permanent (aka nodular) roots of the corn plant are initially pulled from the nodes near the crown area of the young plant (approximately 3/4 inch below the soil surface) and first become visible between the neck stages of leaves V1 and V2. Young roots develop in the form of individual sets or “curls”, starting from the lowest node of the stem and progressing over time acropetally to the node № 6 or so.
The main growth point or meristem of the root is just behind the tip of the root and must remain alive for the root to develop normally.
The roots elongate downward primarily in response to gravity (i.e., a positive gravitropic response). There is evidence that roots also respond to soil moisture gradients (hydrotropism), extending toward soil regions with more favorable moisture levels. However, the main factor in the growth of roots down is probably gravity.
If nodular roots begin their initial elongation in dry surface soil but extend down to sufficient soil moisture at deeper depths before the meristematic tip of the root dries, the root will survive and multiply. When the tip of the root (and the accompanying meristem) dries out before reaching soil moisture, often the entire young nodular root dies.
This is especially true if the axillary meristems along the length of the root (which eventually produce the roots of the added branches) have not yet differentiated or become active.
The drying effect of dry surface soils on young, freshly elongated nodular roots is exacerbated by sunny weather and hot temperatures. Dry soil warms up faster and sharper than wet. On a warm sunny day with temperatures between 80 and 90 degrees Fahrenheit, soil temperatures at 3/4 inch or at depth can exceed lethal levels for young roots. This is especially true for fields without residues cultivated traditionally.
The appearance of withered roots is something that could be imagined; they are wrinkled and discolored. This symptom is unlike any other deadly root stress, including salt damage from fertilizers. These symptoms NO as well as any associated with herbicide damage or insect feeding.
Within a few days, a whole set or “turn” of nodular roots may appear and die. When this happens with the first set of roots (node № 1), when they begin to lengthen (between leaf stages V1 and V2), the young plant survives on what is left in the core stock and what the seed roots provide in terms of moisture and nutrient uptake until the next set of nodular roots develops and strengthens.
If subsequent sets of nodular roots die in the same way, the plant continues to depend on the nucleus and support of the seed roots.
In fact, it’s amazing to me how an aboveground species of a plant whose nodular roots dry up and die can look pretty normal until a fatal windy day when the mesocotyl just can’t support the plant anymore and it literally falls to the ground.
“Disc” corn plants NO technically root; they are simply broken in the mesocotyl below the crown area of the plant. Obviously, the health of the mesocotyl and seed roots determines whether the affected plant can “linger” until there is a decent “soaking” of the rain to replenish the soil moisture level.
I started this article by telling you that “bulk corn” syndrome is a classic example of the importance of stress versus time depending on the stage of plant development. Rooting of young plants is most vulnerable to exposure to dry surface soils until the nodular root system is well rooted (approximately V5 or V6).
Thus, “disc corn” is more common in a field with younger, newly planted corn than in a neighboring field of older, previously planted corn whose nodular root development is further away.
What can be done to alleviate the problem?
Unfortunately, very little can be done to prevent the situation from getting worse. Growing rows can stimulate the development of new nodular roots if moist soil is poured around the base of the plants. However, if the soil is dry enough to cause the problem in the first place, there is probably very little moist soil, small enough that it can be grown by row tillage.
The ultimate solution to the problem is good rain or at least enough rain to support the development of new nodal roots long enough for the roots to reach deeper and hopefully wetter soil conditions before the top of the soil again dry up.
Reminders or tips on foresight.
- “Rootless” corn grows easier at extremely shallow sowing depths, resulting in nodular roots that start closer to the soil surface than at normal depths of about 3/4 inch. This is one of several reasons why growers should not choose a planting depth of less than about 1 to 1-1 / 2 inches.
- Conversely, an unusually deep planting (more than 2 inches) does not result in an unusually deeper initial elongation of the roots, because the light-mediated elongation of the mesocotyl during emergence results in the crown of the seedlings being at about the same depth (3/4 inch) ) below the soil surface.
- Erosion of furrows after planting as a result of heavy rains can cause “shallow planting” of seeds as a result of removal of the top layer of soil.
- Shallow soil compaction as a result of fine tillage of fields that are “slightly on the wet side” can limit the initial development of nodular roots of shallow and often dry soil over compacted layer.
- Open seed cracks as a result of planting without treatment “on the wet side” can contribute to drying and death of the initial development of nodular roots, if the original nodular roots dry out before they successfully penetrate the side walls of the furrow.
https://agfax.com/2022/06/14/indiana-rootless-or-floppy-corn-syndrome/ “Rootless” or “disc” corn syndrome – AgFax