When is the Best Time to Start Corn Harvest?

Erick Larson, State Extension Specialist - Grain Crops
By Erick Larson, State Extension Specialist - Grain Crops July 21, 2012 21:26

When is the Best Time to Start Corn Harvest?

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Corn harvest will be upon us much sooner than normal and expectations are generally much higher than recent years.  However, we still need to get this corn crop out of the field and safely deliver it to market.   Methods to successfully harvest your corn crop may vary depending on several factors.

Field grain drying rate: Corn normally dries about 0.6% per day in Mississippi after it reaches physiological maturity or black layer (when grain moisture is around 30%) down to 15% moisture.  The “black layer” is an abscission layer that effectively cuts off moisture and nutrient transfer between the plant and the grain. Thus, corn grain drying rate after physiological maturity is primarily dependent upon environmental conditions. The drying rate is usually faster when grain moisture is high and slows as it dries and the disparity with the environment diminishes.  Although ample soil moisture may sometimes temporarily keep plants green after grain matures, using a harvest aid to kill green corn leaf tissue will have little or no significant effect on corn grain drydown rate, since there is no longer any active moisture transfer between plant and grain, and husks senescence (naturally die) near physiological maturity.  Furthermore, since corn is an annual plant, leaves will naturally die shortly after maturing anyway.  Some ear characteristics, including husk senescence timing, husk coverage, husk tightness, and kernel characteristics may influence hybrid drying rate, but are generally are less important than weather conditions.  Given normal environmental conditions, corn should dry faster than normal at high moisture and slow as grain moisture evaporates and becomes closer to equilibrium with the environment.  However, when rainfall persists, along with cloudy days, high humidity and low temperatures, grain drydown will slow considerably or be suspended, much like last August and early September. Late-maturing corn will likely dry slower than normal also, because temperatures are usually cooler. In summary, there is little you can do now to effect corn grain drying rate in the field.

The best time to begin harvest may vary considerably, primarily depending upon how long it should 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 harvested in the fall on your farm, determine the potential harvest duration and the relative risk associated with harvest delays or complications. Those potential risks include severe lodging and/or grain quality deterioration, which can result from inclimate weather, insect pest damage, and late-season weed growth.

Moisture Dockage: 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 dockage 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.

Harvest Losses: Harvest losses are just as important as moisture dockage rate in evaluating your harvest timing decision. However, harvest losses are nearly impossible to predict.  Our environment often encourages quick corn drydown and minimal harvest losses, if we have a hot, dry harvest season.  However, the threat of a hurricane or unrelenting rainfall can be conversely disruptive.  The bottom line is that the longer corn stays in the field, the greater the likelihood of substantial field losses. Factors such as stormy weather and southwestern corn borers can cause considerable lodging in unharvested fields. Late summer rainfall can also cause kernel sprouting and promote morningglory and other weed growth, which can greatly inhibit harvest efficiency. Each of these factors may cause substantial field loss, which may considerably outweigh moisture savings.  Thus, the longer it takes you to complete harvest, the earlier you should start harvest.  Try to harvest fields with marginal plant health, such as drought-stricken or questionable stalk quality, or refuge acres (non-Bt hybrids) with considerable insect infestation promptly to minimize losses.   You should closely check for loss while the combine is harvesting and make adjustments accordingly. Two corn kernels per square foot or one dropped ear per 100 feet of row equals about 1 bushel per acre yield loss. Research generally indicates combine efficiency is best (harvest losses are lowest) when corn grain moisture is about 20-22%. 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.  Thus, you should generally strive to finish harvest before grain moisture falls below 15%.

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Erick Larson, State Extension Specialist - Grain Crops
By Erick Larson, State Extension Specialist - Grain Crops July 21, 2012 21:26
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