The type of corn most widely planted in Ohio and across the U.S. is yellow dent. High grain and silage yield potential, high feed value, and availability of adapted superior hybrids account for the widespread use of yellow dents. Yellow dents have the highest content of carotene (vitamin A) of the cereal grains. Other types of corn include flint, pop, waxy and sweet. Most specialty corns have unique kernel characteristics that determine its use and how it is grown.
Because most specialty corn hybrids (including white dent, waxy, high oil, and popcorn) are grown under contract, it is advisable to identify a market before planting. Also, some specialty corn processors specify certain hybrids and cultural practices they want growers to use. Contracts for growing specialty hybrids usually offer a premium over the yellow dent price to compensate for the lower yield potential and the special handling required to ensure high grain quality. More information on specialty corns for identity preserved (IP) grain production is available online at: oardc.ohio-state.edu/hocorn/. Some of the specialty corns grown in Ohio and the U.S. in recent years include:
WHITE CORN White corn types are equal to yellow types in carbohydrate content but are deficient in vitamin A. White types are grown primarily for direct human consumption for use in Mexican-style and other corn-based foods including tortillas, corn flakes, corn meal, grits and hominy. Yields of white hybrids are generally not competitive with yellow dent yields. White corn has been among the most widely grown specialty corns but accounts for less than 1 percent of U.S. corn production.
WAXY CORN The carbohydrate or starch granules of regular dent corn consist of approximately 75 percent amylopectin and 25 percent amylose. Waxy corn has nearly 100 percent amylopectin. Waxy corn was initially recognized as a valuable source of industrial starch. The stability and clarity of amylopectin starch make it highly suitable as a food thickener. Waxy corn has also been considered as a potential animal feed. Feeding trials with waxy corn hybrids have occasionally shown a benefit, but they have not been consistent. Changes in feed efficiency and production have been insignificant, but usually in favor of the waxy corn hybrids. Yields of waxy corns are generally lower than those of yellow dent corn.
HIGH-LYSINE CORN The quantity of two essential amino acids in yellow dent corn, lysine and tryptophan, is below nutritional requirements for humans and nonruminant (single stomached) animals, such as pigs and chickens. High-lysine corn corrects this deficiency and may offer advantages in feeding rations. Adapted high-lysine corn hybrids are limited in number and have generally been lower in grain yield than normal dent varieties. The softer kernels of some high-lysine corn hybrids are more vulnerable to breakage at harvest, which has led to a higher incidence of kernel or ear rot.
HIGH-OIL CORN High-oil corn (HOC) contains 50 to 100 percent more oil than normal yellow dent corn, which averages about 4 percent oil on a dry weight basis. High-oil corn has been promoted as a livestock feed because it has greater energy value than normal yellow dent corn and can replace more expensive dietary sources of fats and proteins. Feeding trials with HOC indicate that it has improved feed efficiency and results in increased rate of gain over conventional corn. However yields of HOC are lower than conventional hybrids. In the late 1990s, HOC acreage increased to more than one million acres. Since then, HOC acreage has dropped sharply. A major factor contributing to this decline is the availability of cheaper sources of oils and fats which compete with HOC as an energy source in livestock feed rations.
These specialty corns must be grown in isolation from yellow dents to prevent cross-pollination and maintain purity standards required by the end user. Separation distances recommended by seed companies range from 60 to 300 feet depending on the specialty corn being grown. These distances can often be adjusted if harvested grain is separated by varying numbers of border rows from the rest of the field.
POPCORN Popcorns are essentially small-kerneled flint corns and are among the most primitive of the surviving races of corn. Kernels contain a hard endosperm with only a small portion of soft starch. Popcorns are generally either pearl or rice types. Pearls have smooth, rounded crowns, and rices are pointed. Heating the kernel turns the moisture inside the soft starch in the center into steam that explodes the kernel inside out. The greater the expansion, the higher the quality. Hybrids differ as to kernel quality, which also includes flavor, tenderness, absence of hulls, color, and shape. Popcorn hybrids usually yield less than half of normal dent hybrids. To achieve maximum quality, minimize mechanical damage and dry with low heat to a moisture of 13.5 percent. Overdrying and kernel damage result in reduced popping volume. Handling and quality are extremely important aspects of popcorn production. From an agronomic standpoint, popcorn must be planted to mature before frost, and herbicide programs must be labeled for popcorn. Fertility programs for popcorn and conventional yellow dent corn can vary, e.g., pay close attention to potassium fertility to guard against poor stalk quality and lodging. Most popcorn in the U.S. is grown under contract for processors and companies. Growers producing popcorn commercially generally follow cultural practices, plant popcorn hybrids, etc., specified by these companies. The isolation requirements for popcorn are not as critical as they are for other specialty corns because some popcorn hybrids are dent-sterile and cannot be pollinated by conventional dent corn hybrids.
Several seed companies have evaluated their existing conventional grain hybrids to determine which are best suited for ethanol production using the wet milling and dry-grind ethanol production methods. Most of the current ethanol output is produced using the dry-grind corn process, whereas wet milling plants (corn refineries) account for the remainder. The dry-grind method produces more gallons of ethanol per bushel of corn grain. Hybrids with high levels of extractable starch are best suited for ethanol production using the wet milling procedure. Such hybrids have been characterized as high extractable starch (HES) hybrids. Hybrids best suited for the dry-grind procedure generally contain high total fermentables and have been characterized as highly fermentable (HTF – high total fermentables) corn hybrids. Hybrids with HTF may not necessarily include the HES trait, nor is either trait necessarily correlated with total starch content. Some hybrids naturally release a higher percentage of the kernel’s starch in the wet milling process. The HES trait is related to the extractability of starch from the kernel. Total fermentables are the sum of all starch and simple sugars that can be utilized by yeast cells used in the fermentation process to produce ethanol. Many hybrids with HES or HTF have high grain yield potential and are widely adapted to Corn Belt growing conditions. Unlike most specialty corn traits, HES and HTF do not require rigorous IP protocols to ensure their expression.
ENOGEN® CORN Enogen® corn is a special type of corn developed and introduced by Syngenta for ethanol production. It contains a transgene from a bacteria that produces alpha amylase, an enzyme that breaks down corn starch into sugar. Presently alpha amylase enzyme is added to corn in a liquid form during the ethanol production process. Corn hybrids with the Enogen trait technology (i.e., Enogen corn) express alpha amylase enzyme directly in the corn kernel, eliminating the need for liquid alpha amylase in dry grind ethanol production. To prevent contamination of commodity grain by Enogen grain, Syngenta has established a stewardship program. Management practices that farmers under contract are required to follow include planting buffers of non-Enogen corn around fields planted to Enogen corn, storing the Enogen grain
in separate bins, and cleaning planters and combines between uses.