As usual, the conversations around the tables at the Chat 'n Chew Cafe over the weekend involved a mix of good news and bad news about the current corn crop in Indiana. The optimists over in the corner booth were reveling over the recent string of sunny, warm days that has finally given the growth of the first-planted corn a kickstart. The pessimists up at the counter, though, were worried about the effects of rapidly drying surface soil on the root establishment of later-planted corn.
Let's recall earlier discussions on root development in corn. The nodal (permanent) roots begin to elongate near the crown of the seedling shortly after emergence and are distinctly visible by growth stage V1 (one visible leaf collar). An individual set of nodal roots forms at each stalk node below-ground plus one or more above-ground nodes. By growth stage V6, the nodal roots should be the main root system of the plant. The time period between growth stages V1 and V6, therefore, is critical in determining the success of the corn crop's root establishment.
Rapid drying of the surface soil layers during this critical time period can stunt the growth and development of the nodal root system. Warmer than normal temperatures, coupled with strong winds, can dry the upper inch or more of soil very quickly. Root 'buds' from any given stalk node that begin to elongate in dry soil or in soil cracks will quickly cease growth due to insufficient soil moisture. If the soil remains dry long enough, the root tips may dessicate and die.
If dry surface soil and/or hot, dry weather prevail, several sets of nodal roots may fail to form, giving rise to the rootless corn phenomenon. Affected plants are forced to depend on the seminal roots, seed reserves, and mesocotyl for nourishment, when normally this life support system has already taken a backseat to the nodal root system.
In addition to the nutrient stress imposed on the plants by not having an adequate permanent root system, the rootless phenomenon can eventually lead to the floppy corn syndrome. These plants are technically not root-lodged, they are simply broken over at the base of the stem near the crown area.
The permanent roots will appear stubbed off but not eaten. The tips of the roots will be dry and shriveled. These symptoms are unlike any associated with herbicide injury or insect feeding. Because several sets of roots may not have formed below-ground, the crown may "appear" to be at or above the surface.
The important thing to remember is that roots will not develop in dry soil. They will not grow toward moisture. If roots are already in moist soil, however, they may proliferate rapidly enough and appear to 'follow' moisture down as the soil dries. Row cultivation may throw enough moist soil around the stalks of the plants to encourage root development and provide some structural support. However, the ultimate answer to the problem is a soaking rain before the whole field has 'flopped'.
Return to the the Chat 'n Chew Cafe.
The Corn Growers Guidebook , a WWW resource for corn management systems in Indiana and the eastern CornBelt.
Purdue University Agronomy Extension WWW Home Page.
Purdue Agronomy On-Line! , Purdue's Agronomy Department WWW Home Page.