Joel Ransom, North Dakota State University Extension agronomist, says there are six things that affect corn root growth. It's possible you can manage some of them to achieve high yields. The six are:
1. Soil temperature. The optimum soil temperature for corn root development is 79 degrees F; there is little or no growth below 50 degrees F. 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 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.
2. 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"
3. Excess soil moisture. Excess moisture 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 rots 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.
4. Nutrient status. Root growth is favored by phosphorous. 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 seedlings that typically have restricted root growth due to cold soil temperatures. A pop up fertilizer, however, will not always solve problems like those pictured. 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.
5. 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.
6. Insect damage. The most common root damaging insects in North Dakota are white grubs, wireworms and corn root 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.