The amazing corn seed

Spring weather has brought challenges for local farmers to get their corn acres planted. Markets will be paying attention to the planting reports as future grain prices may be affected by the final number of planted acres across country. But for now, let's talk about the corn seed — which is quite a miracle in itself. Something that is slightly more than a half inch in length and even less than a half inch wide has the ability to produce a six-foot plant with 18 to 20 leaves and one or more ears with 500 to 1,000 kernels. Consider what is contained in a single corn seed. It has the cells and nutrients for the first six leaves and the first root system of the new plant. This nutrient package has enough energy and minerals to sustain a young corn seedling for about three to four weeks after germination. This amazing biological package consists of three parts: a pericarp, endosperm, and embryo. The pericarp is a fancy term for seedcoat, which Lentz protects the seed from attacking soil fungi and bacteria. The endosperm consists primarily of starch but also has important nutrients, proteins and oils. Its job is to provide the new plant food and energy until the permanent roots become fully functional, which is about four weeks after germination. The embryo has all the cells that will become the first six leaves and the seedling root system. Along with these cells are enzymes and other substances important for germination and growth. Once placed in the soil, these substances in the embryo will be triggered when the seed has detected the proper levels of moisture, temperature and oxygen. Under the right conditions, germination will become visible within two days. The root system is the first part of the seed to emerge in the germination process. The root structure emerging from the seed is called the radicle. The primary role of the seedling root system is to anchor the plant and provide water; the endosperm will provide needed nutrients at this time. The second part of the germination process is the emergence of shoot tissue. The growing shoot will be pushed to the soil surface by a structure called the mesocotyl, which will continue to elongate until the shoot is exposed to sunlight. Sunlight will then trigger hormones that will stop mesocotyl elongation and develop the crown or hub, which will form about three quarters to one inch below the soil surface at the top of the mesocotyl. The crown or hub of the young seedling is the control center for the developing plant. Initially the growing point can be found here. The growing point is a collective term for cells that will eventually differentiate and become leaves, ears, and the tassel. The growing point will gradually move up the developing plant stem (stalk) until it reaches the top at tasseling. Since it starts below the soil surface, the first six leaves produced from the seed may be damaged by frost, hail, or other factors without injury to future leaves and reproductive structures. The seed will be directly responsible for the first six leaves and has provided a root system that anchors the plant and provides water during the transition between seedling roots and the establishment of the permanent crown or nodal roots. By the time the sixth leaf is fully extended, the plant will be 12 to 18 inches tall and crown roots will have become the main root system. The corn plant is not considered established until the crown roots have taken over the responsibility of absorbing water and nutrients and supporting the plant. It takes three to four weeks after germination for crown roots to become the only root system. The seed will have exhausted its stored nutrients by the time it reaches 12–18 inches in height. With the permanent roots established, the corn plant enters a rapid growth stage and will have a high demand for nutrients such as nitrogen. Farmers will have added fertilizer before this time to insure adequate nutrients are available to these plants. and the seed will no longer be providing nutrients. Farmers also know that weeds will cause the most yield loss when left uncontrolled during the first four weeks of the seedling stage. Their herbicide programs are designed to control weeds at planting and through the early part of the growing season. Corn plants become very competitive against weeds once they reach 18 inches and begin their rapid growth stages. The seed has done its part after the corn plant becomes established about four weeks after germination. The farmer has protected the seedlings from weeds during this time and has added nitrogen to feed the rapidly growing plants. For the rest of the growing season, the plants will be on "auto pilot" and the farmer will mainly protect the plant from insects and diseases. After all of this effort, only a remnant of the seed may be found in the soil. Even at tasseling, if an individual carefully digs up a plant they may find the shell of a pericarp and a shriveled mesocotyl in the center of the root crown. On a side note, farmers are always interested in how soon corn plants will emerge after planting. Assuming conditions were right for germination at planting, farmers can estimate the time of emergence by counting growing degree days. Plant developmental stages will occur after so many growing degree days have accumulated. To determine the number of growing degrees for each day, take the average of the high and low temperature for the day and subtract 50. Since the corn plant grows between 50 and 86°F, count any daily high temperature above 86 as 86 for the high and any low temperature below 50 as 50 for the daily low. Add the growing degrees for each day to determine the accumulated growing degree days. Agronomists have determined that the corn plant will require about 120 growing degree days after planting to emerge, providing the seed had adequate soil moisture and other needed germination requirements. So, based on the Findlay airport weather data and counting back from May 18, corn should have accumulated more than 120 growing degrees if planted before May 9.. As I think about how the corn plant develops, I am reminded that corn as a grain sustains life and as a seed in the ground it becomes new life. The corn plant is amazing, and farmers get the pleasure of being a part of this miracle. Ed Lentz is agriculture and natural resources educator with Ohio State University Extension — Hancock County.