Originally published May 2000, Revised Apr 2009
URL: http://www.kingcorn.org/news/timeless/Roots.html
Root Development in Young Corn
R.L. (Bob) Nielsen
Agronomy Dept., Purdue Univ.
West Lafayette, IN 47907-2054
Email address: rnielsen
at purdue.edu
uccessful
emergence (fast & uniform) does not guarantee
successful stand establishment in corn. The next crucial phase is the establishment
of a vigorous nodal root system. Success is largely dependent on the initial
development of nodal roots from roughly V2 (2 leaves with visible collars) to
V6.
Corn is a grass and has a fibrous type root system, as compared to soybeans or alfalfa that have tap root systems. Stunting or restriction of the nodal root system during their initial development (e.g., from dry soil, wet soil, cold soil, insect damage, herbicide damage, sidewall compaction, tillage compaction) can easily stunt the entire plant’s development. In fact, when you are attempting to diagnose the cause of stunted corn early in the season, the first place to begin searching for the culprit is below ground.
To better understand rooting development and problems associated with root restrictions, it is important to recognize that root development in corn occurs in two phases. The first phase is the development of the seminal or seed root system. The second phase is the development of the nodal or crown root system.
Corny Trivia: Sometimes you may hear the seminal root system referred to as the primary root system and the nodal root system as the secondary root system. This classification was described by Cannon (1949) and certainly makes chronological sense but always confuses me from the standpoint of importance to the plant.
The Seminal (Seed) Root System
Seminal (seed) roots originate from the scutellar node located within the seed embryo and are composed of the radicle and lateral seminal roots. The radicle emerges first and elongates towards the tip end of a kernel. The lateral seminal roots emerge later from behind the coleoptile and elongate towards the dent end of a kernel.
Click on image to open a larger version.
 V2 corn seedling. |
 Seminal and nodal roots of V2 seedling. |
Elongation of the stalk tissue begins between leaf stages V4 and V5. Elongation of the internode above the fifth node usually elevates the sixth node above ground. Subsequent elongation of higher-numbered stalk internodes will result in higher and higher placement of the remaining stalk nodes. Sets of nodal roots that form at above ground stalk nodes are commonly referred to as “brace” roots, but function identically to those nodal roots that form below ground. If surface soil conditions are favorable (moist and not excessively hot), brace roots will successfully penetrate the soil, proliferate, and effectively scavenge the upper soil layers for water and nutrients.
Corny Trivia: 
Root
hairs are lateral extensions of root epidermal cells, grow to a length of several
millimeters, and number about 200 per sq. millimeter (Gardner et al.,
1985). Their typical life span is only about 2 days at moderate temperatures
and less so at higher temperatures (Gardner et al., 1985). Root hairs are visible
even on the radicle root of a young seedling. Collectively, the surface area
represented by root hairs is very large and can account for a large share of
nutrient and moisture uptake by the plant.
A split stalk of an older plant will reveal a “woody” triangle of stalk tissue at the bottom of the corn stalk. This triangle is typically comprised of four stalk nodes, one on top of the other, whose associated internodes do not elongate. The first internode to elongate is the one above the fourth node, which elongates about 1/4 to 1/2 inch, above which is found the fifth node (usually still below or just at the soil surface). Consequently, five sets or whorls of nodal roots will usually be detectable below ground (one set for each of the below ground stalk nodes).
Click on image to open a larger version.
 First five sets of nodal roots identified on a split
stalk of corn. |
 Length of internode between 4th and 5th nodes of
corn. |
Effects of Root Damage in Young Corn Plants
Even though the seminal root system contributes little to the season-long maintenance of the corn plant, early damage to the radicle or lateral seminal roots can stunt initial seedling development and delay emergence. Such damage will not necessarily cause immediate death of the seedling as long as the kernel itself and mesocotyl remain healthy, but may result in the seedling leafing out underground. As more and more nodal roots become established over time, damage to the seminal root system will have less and less impact on seedling survival.
Examples of seminal root damage include imbibitional chilling injury, post-germination injury from lethal or sub-lethal cold temperatures, and “salt” injury from excessive rates of starter fertilizer placed too close to the kernel. Symptoms of such root damage include retarded root elongation, brown tissue discoloration, prolific root branching, and outright death of root tissue. If the radicle root is damaged severely during its emergence from the kernel, the entire radicle root may die. Once the radicle has elongated a half-inch or so, damage to the root tip will not necessarily kill the entire root, but rather axillary root meristems may initiate extensive root branching in response to damage to the apical meristem.
Click on image to open a larger version.
 Delayed emerger w/ healthy lateral seminal roots but damaged radicle root. Coleoptile is splitting prematurely and seedling will likely leaf out underground. |
 Closer view of premature splitting of coleoptile. |
 Closer view of damaged (dead) radicle root. |
 Another delayed emerger with healthy lateral seminal roots and damaged, but alive, radicle root. |
 Closer view of damaged radicle root tip with numerous adventitious roots. |
Corn seedlings transition from dependence on kernel reserves to dependence on nutritional support by the nodal roots around the V3 leaf stage. Damage or stress to the first few sets of developing nodal roots during the time period V1 to V5 can severely stunt or delay a corn plant’s development. Damage to the first few sets of nodal roots forces the young seedling to continue its dependence on kernel reserves longer than is optimum. If the kernel reserves are nearly exhausted, continued seedling development is easily stunted and seedling death is not uncommon. Typical stresses that can stunt initial nodal development include fertilizer salt injury, seedling diseases, herbicide injury, insect feeding damage, excessively wet or dry soils, soil compaction (tillage or planter).
Corny Trivia: The primary meristem of a root is located near the root tip. Elongation of cells behind the meristem leads to elongation of the root.
A somewhat uncommon, but dramatic, stunted root symptom is what is referred to as the “floppy corn” or “rootless corn” phenomenon. This problem occurs as a result of the detrimental effects of excessively dry surface soil near the time of initial nodal root elongation in young (V2 to V4) corn plants. Young nodal roots that emerge from the crown area of the plant will die if their root tips (and associated meristematic areas) desiccate prior to successful root establishment in moist soil. The crown of a young corn plant is typically located only 3/4 inch or so below the soil surface and so is particularly vulnerable to dry upper soil conditions.
Related References
Cannon, William Austin. 1949. A Tentative Classification of Root Systems. Ecology 30[4], 542-548.
Gardner, Franklin P., R. Brent Pearce, and Roger L. Mitchell. 1985. Physiology of Crop Plants. Iowa State Univ. Press, Ames, IA.
Nielsen, RL (Bob). 2004. Over-Extended Mesocotyls and Floppy Corn Syndrome. Corny News Network, Purdue Univ. [On-Line]. Available at http://www.kingcorn.org/news/articles.04/FloppyCorn-0624.html. (URL accessed 5/5/09).
Nielsen, RL (Bob). 2007. Be on the Alert for Floppy, Rootless Corn. Corny News Network, Purdue Univ. [On-Line]. Available at http://www.kingcorn.org/news/articles.07/Floppy-0523.html. (URL accessed 5/5/09).
Nielsen, RL (Bob). 2009a. Germination Events in Corn. Corny News Network, Purdue Univ. [On-Line]. Available at http://www.kingcorn.org/news/timeless/GerminationEvents.html. (URL accessed 5/5/09).
Nielsen, RL (Bob). 2009b. The Emergence Process in Corn. Corny News Network, Purdue Univ. [On-Line]. Available at http://www.kingcorn.org/news/timeless/Emergence.html. (URL accessed 5/5/09).
Nielsen, RL (Bob). 2009c. Visible Indicators of Germination in Corn. Corny News Network, Purdue Univ. [On-Line]. Available at http://www.kingcorn.org/news/timeless/GerminationGallery.html. (URL accessed 5/5/09
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