Corn Grain Drydown and Strategies for Successful Harvest

Erick Larson, State Extension Specialist - Grain Crops
By Erick Larson, State Extension Specialist - Grain Crops August 7, 2021 10:51

Corn Grain Drydown and Strategies for Successful Harvest

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Corn harvest should ramp up soon as grain matures and dries down to an agreeable moisture for harvest. Corn maturity is generally later than normal this year, primarily related to lower than normal heat unit accumulation, despite a lot of early planting opportunities this spring. Thus, you are likely eager to successfully get this crop out of the field and safely deliver it to market. Understanding how weather and other factors affect grain drying, potential harvest losses, moisture dockage, and even aflatoxin can greatly help improve your harvest efficiency and success.

Corn grain maturity and the transition to drydown – When corn reaches maturity a “black layer” forms at the kernel base when hard starch accumulation is complete. This black layer is an abscission layer that effectively cuts off moisture transfer and all physiological activity from the plant. Thus, grain drying rate is essentially completely dependent upon environmental conditions, rather than plant health or disposition. Furthermore, since corn is an annual plant, the vegetation will naturally senescence or die after maturity, particularly when temperatures are hot and/or soil moisture is limited. Consequently, using a harvest aid will have little or no effect on grain drying, since the black layer halts moisture flow to the grain, and the plants are naturally dying.

The black layer separates the kernel from the cob, making drying rate dependent on ambient conditions.

Grain drying rate in the field – Weather and climatic conditions basically dictate corn grain drying in the field. Fortunately, we are normally blessed with plenty of heat and dry weather during August and September, so our corn drying rates are usually considerably greater than in Corn Belt states north of us. However, when rainfall persists, along with cloudy days, high humidity and cool temperatures, grain drying will slow considerably or be suspended. Mississippi corn normally dries at an average rate of 0.6% per day from physiological maturity or black layer (when grain moisture is around 30%) down to 15% moisture. However, this drying rate will usually be faster when grain moisture is high, and then scales back as it drops into the teens, when the disparity between grain moisture and the environment diminish. Accordingly, you may see grain moisture fall about 0.75% per day or more the first ten days or so after physiological maturity.

Factors that affect harvest efficiency and losses – The best time to begin corn harvest may vary considerably, primarily depending upon how long it might take to harvest your crop. This will depend on how many acres you have, relative to your harvesting capability, including combine, trucking, and storage capacities. These factors, along with the other crops you grow on your farm, determine the potential harvest duration and the relative risk associated with harvest losses, delays or other complications. Those potential risks include various types of stalk lodging and/or grain quality deterioration, which can result from stormy weather, insect pest damage, and late‐season weed growth. The most significant weather-related threat to Mid-South corn is likely high winds promoting stalk lodging. One dropped ear per 100 feet of row or two corn kernels per square foot or equals about 1 bushel per acre yield loss. The bottom line is that the longer corn stays in the field, the greater the likelihood of substantial field losses and complications.

Lodging caused by storms can substantially increase harvest loss and hinder harvest progress.

The effect of grain moisture on dockage and yield ‐ Corn may be harvested any time after grain reaches physiological maturity, which occurs at around 30% moisture. However, corn may not be safely stored until considerable moisture loss occurs. Thus, grain elevators discount wet corn to account for drying expenses and moisture weight loss during drying. Moisture dockage schedules between elevators may vary, so thoroughly compare rates. Most schedules discount about 2.5‐3.0% per each percent moisture above the standard, and may increase as moisture content rises. Water evaporated during drying (shrinkage) accounts for 1.18% of the grain weight per percent moisture. You lose this weight regardless of whether you sell wet grain to the elevator, dry it mechanically or let the grain field dry. Thus, you should subtract this value from the dockage rate to show your realized or “actual” dockage. Furthermore, corn delivered to market at less than the standard moisture weighs less, so you are essentially docking yourself (1.18% per percent moisture) if you do so.  For this reason, along with mounting harvest losses, you should generally strive to finish harvest before grain moisture falls below 15%.

Grain management during and after harvest – Although harvesting corn earlier will normally reduce potential field and harvest losses, it does require considerably more effort to properly handle and store grain, especially in our climate. Grain is a living organism which may spoil quickly when the grain moisture and temperatures are high. For example, temperatures during harvest in the South will be well above 85 degrees F, which is a stark contrast to the Corn Belt. Furthermore, moist grain and high temperatures also cause fungal growth to flourish, potentially causing aflatoxin to escalate rapidly in improperly stored or handled grain. This has created some aflatoxin issues in past years, especially when unseasonable rainfall tempered field drying. If you are hauling high moisture corn directly to market, it is vital to deliver it as quickly as possible. Do not store grain in trucks, grain carts, combines, grain bins, or any non-aerated site for more than 4 to 6 hours. Swift and proper handling is also critical if you intend to dry your own corn. Corn should be dried to less than 15% moisture with 24 hours after harvest. High capacity, continuous flow driers are generally capable of rapidly drying corn to 15 percent moisture or less, but in-bin drying or aeration systems are generally not capable of this goal, and thus, present serious management challenges for high moisture corn. Dried corn should also be aerated and cooled shortly thereafter as well. Fungal growth and associated aflatoxin development becomes dormant when grain moisture drops to about 12 percent, especially when grain temperatures decline to around 55 degrees F, so this should be your goal for long-term storage through the fall and winter.

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Erick Larson, State Extension Specialist - Grain Crops
By Erick Larson, State Extension Specialist - Grain Crops August 7, 2021 10:51
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1 Comment

  1. Howard August 15, 12:13

    Your comment that harvesting corn should near completion by the time it reaches 15% is interesting. It used to be that we thought that’s when we should start, to prevent dockage loss.

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