Corn reaching maturity about October 1 will normally dry slowly in the field due to cooler ambient temperatures. Standing corn in the field may dry about 1.5 to 3 percentage points per week during October and 1 to 1.5 per week or less during November, assuming normal North Dakota weather conditions. Table 1 below provides field drying rates for corn in Minnesota.
Corn has a moisture content of about 32 percent when it reaches maturity. If it has a moisture content of 32 percent on Oct. 1, it may only dry to about 22 percent moisture by Nov. 1, assuming normal North Dakota climatic conditions. Field drying normally is more economical until mid-October, and mechanical high-temperature drying is normally more economical after that.
Table 1. Field drying rates for corn in Minnesota.
|Date||Grain moisture loss|
(% per day)
|September 25-October 5||0.50-0.75|
|After October||>very little|
|Source: Hicks (2004)|
Balancing potential field losses with drying costs
Assure corn stalks and shanks are strong if considering leaving very high moisture corn in the field. Field losses can range from minor to severe. Compare the cost of drying versus losses associated with leaving the corn in the field. The propane cost per bushel per point of moisture removed can be estimated by multiplying the propane price per gallon by 0.02. For example the cost to remove 10 points of moisture using $2.00 propane is $0.40. Dividing the propane cost by the corn price provides the percentage of corn losses that will equal the drying cost. ($0.40/$3.00=0.13 or 13%) Also, verify the impact on insurance of leaving the corn in the field.
Storage in a poly bag is a good storage option, but it does not prevent mold growth or insect infestations. Grain should be dry when placed in a grain bag. Higher moisture corn in a bag should be considered as very short-term storage and only at or near freezing temperatures. At moisture contents exceeding about 25 percent, ensiling may occur at temperatures above freezing and prevent the corn from being dried and sold in the general market. Select an elevated, well-drained location with the surface prepared to prevent punctures for the storage bags, and run the bags north and south so solar heating is similar on both sides of the bag. Wildlife can puncture the bags, creating an entrance for moisture and releasing the grain smell, which attracts more wildlife. Monitor the grain temperature at several locations in the bags.
Drying high moisture corn
Corn above 21 percent moisture should not be dried using natural-air and low-temperature drying to minimize corn spoilage during drying. Because the drying capacity is extremely poor at temperatures below 35 to 40 degrees, little drying is typically possible using a natural-air system after about November 1. Adding heat does not permit drying wetter corn and only slightly increases drying speed. The primary effect of adding heat is to reduce the final corn moisture content. When outdoor temperatures average near or below freezing, cool the corn to 20 to 25 degrees for winter storage and finish drying in April to early May. Limit the corn depth to about 20 to 22 feet to obtain an airflow rate of 1 to 1.25 cubic feet per minute per bushel which is necessary to dry the corn before deterioration occurs. Turn fans off during extended periods of rain, snow or fog to minimize the amount of moisture the fans pull into the bin.
Using the maximum drying temperature that will not damage the corn increases the dryer capacity and reduces energy consumption of a high-temperature dryer. Removing a pound of water requires about 20 percent less energy at a drying air temperature of 200 F than at 150 F. Follow the dryer manufacturer's recommendation, but generally recommended plenum temperatures when drying corn are 210 to 230 F.
Be aware that excessively high drying temperatures may result in a lower final test weight and increased breakage susceptibility. In addition, as the drying time increases, high-moisture corn becomes more susceptible to browning. A cross-flow dryer that moves corn from the inside to the outside of the drying column, varies the corn flow rate across the drying column or varies the corn's exposure to the drying air is more likely to maintain corn quality.
Removing debris that accumulates on or in a dryer is more critical when outside air temperatures are cold because condensation can develop on the dryer, creating a wet surface on which debris can collect. The debris may reduce airflow through the dryer, decreasing the dryer's capacity and creating a fire hazard.
More mechanical damage occurs when harvesting high moisture corn which affects the storage life of the corn. Dry low-test-weight and corn with increased damage a percentage point lower in moisture content than normal. Cooling the grain in storage to about 20 to 25 degrees for winter storage in northern corn-growing regions and near freezing in warmer regions is more important than for mature sound corn. Check immature and damaged grain more frequently and do not put immature or damaged corn in long-term storage.
Working with high moisture corn can be hazardous. Become informed of the hazards and recommended safety practices. Do not become a fatality.
For more information, visit the North Dakota State University Grain Drying and Storagewebsite and the University of Minnesota Corn Harvest website.