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Harvesting and Storing Corn

By Dr. Harold Willis

How you go about planting and growing corn depends to a large extent on what you are going to do with it when you get done. Are you growing it for grain? To feed to your animals or to sell? Or are you going to make silage or green chop it? Or perhaps are you growing a specialty crop — sweetcorn for canning, or popcorn?

Each purpose for growing corn has its own set of limitations and desired goals. We will mainly concentrate on growing for grain and for silage (popcorn is harvested as grain, and sweetcorn is harvested early like silage).

Corn waiting for harvest

Generally, when growing corn for grain, you will want to plant a variety that has a short enough growing season to mature before frost, and plant it early to be sure it gives a high yield. The use of a high quality seed and a seed treatment also helps. On the other hand, for silage, mature grain before frost is not necessary, so you can plant a longer season variety and higher population than for grain.

Silage

Ensiling is an excellent method of preserving a nutritious, palatable feed for dairy and feeder cattle, with little waste and easy mechanization. When moist whole corn or ear corn is chopped and packed into an air tight silo (or trench or tube), aerobic bacteria, yeasts, and fungi naturally occurring on the corn plants will begin fermenting the plant material. But in several hours they use up the oxygen they need to remain active, so anaerobic bacteria take over and continue decomposition, producing lactic and acetic acids as by-products.

After about two weeks, conditions are too acid (pH 3.5 to 4.0) for them to remain active, so all microbial activity more or less stops and the silage is preserved. But if there are leaks in the silo or when you begin feeding the silage, oxygen enters and decomposition by bacteria and fungi continues, spoiling some of the silage. Poorly packed silage will also develop pockets of spoilage.

The commonly recommended stage of maturity and moisture for harvesting corn for silage is when the kernels have started to harden and glaze,* or when kernel moisture is from 30 to 35% moisture and the total chopped material is 60 to 70% moisture. Water can be added to nearly ripe corn to bring it to the proper moisture so it will pack well.

*This is true of average corn, but with the high quality corn you can raise on good soil, ensiling can be done when the grain is in the milk stage. At that stage the calcium present in the grain is in a form more readily used by animals. Also, high quality grain will have a lower moisture content than average corn at the same stage of maturity.

There are several materials that are sometimes added to silage for various purposes.

  1. Lactobacillus inoculants serve to introduce the right kind of acid-producing bacteria, to insure correct preservation. Although such bacteria are supposed to occur on the corn naturally, the use of an inoculant can be cost effective.
  2. Ammonia and urea are being added to increase the nitrogen content of the silage. It is said that ruminants can use the nitrogen to make extra protein; thus weight gain or milk production increases. This is a band-aid approach. The animals really don’t need protein as much as high energy foods (carbohydrates, oils). High quality feed will have adequate protein already, or else a high quality supplement such as soybean oil meal should. If urea or ammonia are used, they must be balanced by a high energy content feed or else liver damage can occur. Urea can be toxic in too great amounts, and should be mixed thoroughly in the silage.
  3. Gypsum (calcium sulfate) or sodium sulfate are used as a source of sulfur if urea is added; this should not be necessary if high quality feed is used.
  4. Limestone is used in combination with urea to give increased gains, to neutralize strong acid additives (covered next), or else is added to lower the nitrate content of high nitrate feed. Again, high quality feed eliminates these needs.
  5. Propionic acid or other chemical additives (sulfur dioxide, sodium metabisulfite, phosphoric acid, formic acid, sulfuric acid, hydrochloric acid) short-circuit or speed up the attaining of acid conditions, preventing spoilage at high moisture levels. But the desirable partial breakdown of proteins that would occur by bacteria is also short-circuited. Such preservatives should be unnecessary for high sugar content crops (corn, sorghum, Sudan, small grains) and especially not for high quality crops.
  6. Molasses, ground grain, and other carbohydrate sources, or whey are added to increase feed value and palatability, and at the same time to encourage growth of beneficial silage bacteria and speed up the ensiling process. Whey gives the least satisfactory results.

Nitrates

One serious problem that can arise when the whole corn plant is fed to animals is nitrate poisoning, which at high levels produces oxygen deficiency in the animals, evidenced by blue mucus membranes and chocolate-brown blood. Death follows. Milder sub-lethal cases include vitamin A deficiency (pink eye), thyroid disturbances (iodine deficiency), reproductive difficulties, lower milk production, reduced weight gain, and oxygen deficiency.

In a healthy corn plant, nitrates will be made into proteins and stored in the grain, but under certain conditions this does not occur normally and excess nitrates accumulate in lower leaves and especially the lower stalk. The conditions that favor high nitrates in corn stover are:

  1. High available nitrogen or potassium in the soil (from excessive nitrogen and potassium fertilization)
  2. An extreme shortage of phosphorus or potassium (reduces growth while roots continue to take in nitrate nitrogen)
  3. Drought
  4. Barren stalks (no kernels to store proteins in)
  5. Shading of leaves, either from high plant populations or cloudy weather
  6. A heavy rain after a long dry period (roots absorb much nitrate along with water)
  7. Certain herbicides, especially 2,4-D (prevent nitrates from being made into proteins).

If you are forced to use high nitrate feed, here are some points to consider:

  1. Non-ruminants (hogs and poultry) can tolerate more nitrates than ruminants (cattle, sheep). Feed the nitrate feed gradually throughout a day and increase the amount gradually. That way rumen bacteria can adjust and partly detoxify it. Adding grain, molasses, limestone, or live yeast culture to the feed reduces the effect of high nitrate (corn grain has little or no nitrate). Molasses and grain are high energy foods, giving the animals added strength.
  2. Ensiling high nitrate corn reduces nitrates considerably after a few weeks. Do not feed green-chopped fodder, and cut the stalks high (1 1/2 to 2 feet). Delay harvesting as long as possible, since nitrates decrease in time.
  3. Also check for nitrates in the animals’ drinking water. Nitrates in water are absorbed into the blood faster than from food, and they add to what is in the feed, making the problem worse.

Other methods

Green-chop fodder feeding can be an excellent source of nutritious animal feed if the crop is of high quality. In fact, high quality corn fodder can be a complete ration (if essential proteins, vitamins, minerals, and carbohydrates are present in adequate amounts). High quality corn can also be pelletized or baled like hay at the tassel stage or later. Mixing alfalfa or grass forages, straw, or grain with the corn reduces moisture and may improve feed value.

The ideal goal in growing corn for grain is for the grain to completely fill with high levels of proteins, starches, oils, minerals, and vitamins; to become physiologically mature; to grow dry; and for the plant to stay standing until harvest. Some of those terms or concepts may be new to you, so let’s explain them.

High quality corn will have its kernels packed full of nutrients, and as it matures, excess water will be “pushed out,” and it will grow dry enough to store. Physiological maturity means the kernel has reached its highest dry weight, when no more food is being stored in the grain. It is indicated by a “black layer” that forms at the tip of the kernel. The plant should remain green until maturity or beyond. Early-dying plants, dented or shriveled kernels, low test weight, and high moisture grain all indicate low quality. Something went wrong—perhaps weather stress, low soil fertility in the latter part of the growing season, weeds, pests, diseases, etc.

In case you read over it, let’s repeat: high quality corn should not dent (even “dent” varieties will dent little if at all) and should store without molding as it comes out of the field. That sounds hard to believe, I know. High quality corn may have a fairly high percent moisture (perhaps 24 or 28%), but this is “bound moisture,” which is locked into the stored food molecules. It should store without molding. If such corn is artificially dried down to 13% moisture like ordinary corn has to be, its food value will be greatly reduced. It should not be artificially dried. It will also have a high test weight, say 60 or 62 lbs. All of the above refers to truly high quality corn that has not been cut short by an early frost, not to just above average 56 lb. test weight corn, which probably will have to be dried to prevent mold. Sad to say, too much corn being grown these days is 52, 48, or 46 lb.

High moisture corn

Shelled corn or earcorn harvested early at 25–33% moisture and stored in an air-tight (sealed) silo is an excellent animal feed (if it is of high quality). If it is finely ground and firmly packed, high moisture corn can even be stored in conventional silos or trench silos. Storing high moisture corn eliminates any possible need for drying, but it also eliminates the possibility of selling the corn on the grain market. Preservation with propionic or propionic/acetic acids or sodium metabisulfite is often used to prevent mold; this should not be necessary with high quality corn.

Dry grain

For ordinary harvesting of dry earcorn or shelled corn, the kernel moisture content in the field should be from 21 to 28% for average quality corn. As we have said, high quality corn may be as dry as it will get at a higher moisture content than average corn. For storage of average quality earcorn, the kernel moisture should be below 23%, and below 14% for shelled corn. High quality corn will store without molding at higher moisture. Safe storage time is increased the colder the weather and the lower the kernel moisture content. Ear corn can be stored in cribs without the extra expense of ventilators and drying. Grain bins should be well designed and provide adequate ventilation and temperature control.

Grain drying has become a large, expensive, and seemingly necessary part of growing corn these days. But it is really necessary only for average or poor quality corn or to satisfy legal moisture requirements (which were written for poor quality corn). Drying with too high temperature literally cooks the grain, destroys its life, and greatly decreases its food value.

If you must dry your corn, then you must, but it isn’t always necessary to do it the expensive way, using precious fossil fuel. Field drying on the stalk works well as long as there is little lodging. Low temperature drying (with the air heated only several degrees above the outside temperature) takes longer but saves much fuel and doesn’t harm the grain. It is hardly practical with large amounts of corn in cool, humid climates, however. Solar driers have recently been developed and can be home-made. Plans may be available from your state university extension service.

Mold

Whether in silage, high moisture corn, or dry grain, molds are a ticking time bomb. The potential danger is immense, and a number of disasters have already occurred. Some fungi are harmless and some, like Penicillium, produce materials useful to us. But other fungi produce poisons, called mycotoxins, which can be deadly. The best known mycotoxins are the aflatoxins, produced by Aspergillus fungi, common among the molds that attack poor quality and too-moist grain. Abnormal or unhealthy crops are most often attacked: cracked kernels of stored high moisture grain or crops damaged by hail or early freeze, or suffering stress from drought and insect damage.

Symptoms of poisoning in animals include impaired liver functions, reduced blood clotting, fragile capillaries and hemorrhaging, kidney damage, impaired immunity to diseases, interference with vitamins A and D and with calcium metabolism, anemia, reduced weight gain and production of milk or eggs, and poor reproduction.

An animal’s milk, eggs, or meat can be contaminated by the toxins, and humans can also be exposed by directly eating food products made from moldy grain (cornmeal, grits, etc., also peanuts).
The common practice is to blend moldy grain with good grain to reduce toxins to “safe” levels before feeding to animals. You should be suspect of any ground feed you buy that wasn’t made from your own grain. A black light screening test to detect molds should be made on all batches of grain or feed that you buy.

To prevent molds from starting in your corn, try to grow healthy, stress-free crops and store grain under cool, dry conditions. Chemical additives for high moisture grain to kill molds may be necessary if quality is not very high.

Source: How to Grow Top Quality Corn by Dr. Harold Willis

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