Corn Has Unique Root System

This past week I had the opportunity to drive through the eastern two-thirds of the county. The countryside has a beauty we do not see often. On the negative, the number of acres planted exceeded my expectations. It looks like there will be a few more acres of corn to harvest this fall, anyway, I hope so. The last time we gave corn a good try on the non-irrigated acres, the summer and fall did not produce enough heat units to make corn again.

Compared to wheat, we know that the above ground tissue of corn is much different. This difference extends to the root system.

Corn has two rather distinct rooting systems. The first is comprised of the seminal roots that arise from the seed at germination. The seminal root system is limited in size and function but provides a mechanism for the emerging plant to access nutrients and water. The nodal roots develop about 1 inch below the soil surface beginning at about the first collar leaf stage. Nodal roots (2-10 per node) generally develop from all of the subterranean nodes (typically 5).

By the four leaf stage, the nodal roots are larger and more expansive than the seminal roots. Roots can also arise from corn nodes that are above the surface of the soil. These roots are called brace roots and, if conditions are favorable, are able to penetrate into the soil and effectively extract water and nutrient from the top layer of the soil. Some general factors that affect root growth to consider and manage when possible, that may or may not have application this season.

Soil temperature – the optimum soil temperature for corn root development is 79°; there is little or no growth below 50°. The cool temperatures this spring have generally limited root development causing plants to be pale green or show symptoms of P deficiency. No-till soils with high residue tend to be a few degrees colder than the soils that are tilled. Furthermore, well drained soils warm up faster than wet soils. This could be an advantage of a tiled field if the water table is an issue causing wet conditions.

Inadequate soil moisture – roots will not develop or grow through soil that is below the permanent wilting point. They will follow water in the soil, however, in that they will branch and develop in regions of the soil that have favorable soil moisture even if surface layers are depleted of moisture. If the soil surface is dry, hot or compacted during nodal root development, nodal roots may be limited resulting in young plants that easily lodge. This has been referred to as the ‘rootless corn syndrome’. There were a few reports of this problem last year in North Dakota. I think with the rainfall after planting this year, there will be a few if any problems of rootless corn.

Excess soil moisture – Excess moisture this spring is a much bigger problem for corn root development than inadequate soil moisture. When soils become saturated, the amount of oxygen available to the roots decreases rapidly as plants and microorganisms deplete available sources. Corn roots need oxygen for respiration, cell division and nutrient uptake. Waterlogged conditions can also predispose plants to root lots later in the season, so the ultimate effect of excess moisture may not be known until late in the season. Promoting rapid field drainage can directly benefit root development in wet seasons like this year.

Nutrient status – root growth is favored by phosphorus. Roots will not preferentially grow towards a band of fertilizer but if they grow into one, they will develop more profusely there if nutrients are otherwise limiting. Pop-up fertilizers are recommended in North Dakota in order to enhance P uptake by corn seedings that typically have restricted root growth due to cold soil temperatures. A pop-up fertilizer, however, will not always solve problems. Mycorrhizae fungi also aids corn roots in extracting P from the soil. Add additional P when corn follows a black fallow, canola or sugar beets as these crops/practices reduce the amount of Mycorrhizae fungi in the soil.

Compaction and chemical barriers – Roots are not able to penetrate very compacted layers of soil or grow into layers that are high in salts or calcareous hardpans. For fields with soils known to be prone to compaction, check for compaction layers. A well aggregated, well drained soil will promote root growth.

Insect damage – the most common root damaging insects in ND are white grubs, wireworms and cornroot worm larvae. As part of your scouting program examine the roots for damage from insects. Most root-feeding insects are best controlled with insecticides applied on the seed or at the time of planting or in the case of the rootworm, the use of corn hybrid that is traited with a Bt gene effective against that pest.