Leaves are the factories for photosynthesis, the process responsible for manufacturing sugars essential for plant growth and development and eventual grain yield. Leaf loss close to tasseling is extremely detrimental to corn yield. Leaf loss when the corn plant is young will have only minor effects on yield because the plant can grow more leaves. Leaf loss late in development (late seed fill) will hurt yield very little.
Corn roots are extensive, reaching as deep as 6 to 7 feet in the soil and thoroughly spreading throughout the upper 2 feet or so in the soil. Finer roots have more area for their weight than larger-diameter roots, so they are more efficient at moving into soil and taking up water and nutrients. Root systems branch a great deal, with roots generally getting smaller the farther “down the root” they branch from. Finer roots are often called “root hairs,” but that term technically refers to tiny “threads” that root cells sometimes produce that go out into the soil to help pick up nutrients.
The main root system of the corn plant is the nodal root system, which means that the roots originate at one of the lower stem nodes (“joints”) of the plant. There are usually fives nodes below the soil surface, and the bulk of the root system grows from these nodes. The roots that grow from nodes above the soil surface are called “brace roots,” based on the observation that they appear to help brace the crop from falling over. Brace roots enter the soil some distance away from the stalk so they have a better angle from which to brace the plant. Brace roots also take up water and nutrients, unless the surface soil is dry. If brace roots appear at more than two nodes, there may be a problem elsewhere in the plant, such that excessive sugars accumulate in the lower stem. By the same token, lack of good growing conditions may limit sugars in the lower stem and brace roots may develop poorly or not at all. If there are no problems with high winds during the season, lack of brace roots may not be a problem.
The proportion of roots on a corn crop has been reported at values between 0.1 and 0.7, but there is yet no definitive answer. One difficulty is that the root system reaches its maximum dry weight within a few weeks after pollination, or perhaps six weeks before the aboveground part of the plant reaches its maximum weight. In general, we can probably estimate that there is 1 pound of belowground dry matter for every 4 to 5 pounds of aboveground dry matter. We need to remember that plants spend considerable energy (sugars from photosynthesis) to grow and maintain the root system, meaning that growing large roots will usually be at the expense of crop yield.
Bigger corn root systems are not usually better, though there are sometimes weather and soil conditions under which larger root systems might help plants to avoid water deficits. Root systems require a lot of energy from the plant (leaves) for growth and maintenance, so larger roots often come at the expense of crop yield. Unfortunately, knowing exactly what the optimum root size needs to be for a certain season is impossible.
Early corn canopy closure can have some beneficial results. If the cornfield approaches 90 percent light interception near silking, yield should be maximized. In areas where temperatures are cooler and days suitable for growing a crop are fewer, narrow rows tend to reach 90 percent light interception at tassling more frequently than corn in 30-inch rows. Early canopy closure could help with weed competition and earlier shading of the soil to prevent water loss from evaporation. In some environments these factors may help with yield.
For more information on this or other topics related to corn production, contact your state extension corn specialist or your local extension educator/agent.
Following is the link to the corn extension specialists: state extension corn specialist.