Wet corn and the propane shortage

November 13, 2019 3:31 PM
Blog Post

Update Note: This was first published November 13, 2019. As of November 19, 2019 we are expecting a few days of warm weather; dewpoints will get above freezing. It would be counterproductive to keep the fans on during this period.

The late planting has caused higher moisture corn than normal.  Since most farm dryers and some elevator dryers operate on propane gas (LP), the LP distribution backup has caused wet corn to be held, either in storage, or in the field.   With 36% of acres unharvested as of November 11, Iowa has relatively less wet corn waiting than states to the north and east.  Elevator reports indicate the wet corn is around 20% moisture in central and western Iowa, up to 25% moisture  or higher in northern and eastern Iowa.

The general corn quality in 2019 is below average, due to the record late planting and subsequent immaturity and incomplete grain fill.  Immature corn has lower test weight, lower protein content, and poorer storability (resistance to mold invasion). Replanted corn and very late initially planted corn are also causing large variations in moisture content that cannot be fully evened out in high temperature dryers; there will be pockets of wet grain in the dry corn.  Bin dryers with stirring machines are better at evening out moisture variations but have much lower throughput capacity than high temperature batch or continuous flow dryers. The drying season is pretty much over for low temperature and natural air dryers because the moisture evaporation capacity of cold air is low.

Immaturity has also made 2019 corn harder to dry. Elevators are reporting 5-10% increases in energy use per unit of moisture removed; soft texture makes corn hang on to the water tightly. 

This means the storage life (allowable storage time) is shorter than normal estimates. See: https://crops.extension.iastate.edu/cropnews/2019/10/crop-quality-2019-another-unusual-year-0.

Elevators regardless of fuel source have gotten behind with more moisture to remove, more energy required per unit of moisture, and in many cases higher yields than expected. 

Maintaining uniformly cold grain temperature will be the key to holding wet corn until it can be dried or sold.  Conical piles, both covered and uncovered, are difficult to aerate uniformly, and therefore will experience more storage problems than bins or regularly shaped flat storages with good aeration systems.

Harvested wet corn should be placed immediately in an aerated bin.  Do not leave wet corn on vehicles or un-aerated bins, as this can use significant amounts of the future allowable storage time to be lost.

Grain will cool by evaporation to nearly the dewpoint (temperature at which water will condense).  Dewpoints are very low right now.   The dewpoint is lower than the actual temperature unless the air is 100% relative humidity.  Airflow rates typical for aeration of dry corn (0.1 cfm/bu or higher) will be enough for cooling (not drying). 

Corn can be stored at temperatures below freezing.  The risk is having frozen chunks that either obstruct airflow or jam conveyors.  Frozen corn should be as clean as possible.  Periodically remove grain from the center of bins; this will take out fines, keep the grain moving, keep a roughly level surface for air distribution and provide a sample for temperature measurement if the bin does not have temperature cables or is too deep for surface probing alone. One load should be enough in medium farm bins, less in small bins and more in larger ones.

Pay attention to the weather forecasts and conditions.  You do not want to rewarm the wet corn in a warm spell.  Consider 35F as the upper limit for grain temperatures, for wet corn.  The dewpoint is the critical measurement to follow.  On low humidity days, there can be low dewpoints even with moderate air temperatures.  For example, 50 degree air with 40% relative humidity will have a dewpoint of 30F. 

Update Note: This was first published November 13, 2019. As of November 19, 2019 we are expecting a few days of warm weather; dewpoints will get above freezing. It would be counterproductive to keep the fans on during this period.

Tarped piles that require fan operation to hold the tarp on the pile will face greater risks from rewarming.  Weekly records of exiting air temperatures at each fan, or at the top with upflow aeration, will give indications of temperature stability in the grain mass but will not necessarily identify pockets of heating.

Dry the corn or sell it as soon as you can, even if this means some extra handling. The longer that wet corn stays in a bin, even cold, the higher the risk of spoilage in some places, such as along a wall that gets warmed on sunny days.  Storage life loss shows up in the spring with hot spots, blue eye mold and eventually serious spoilage. 

If drying is slowed but still possible, consider drying to an intermediate moisture (17-18%), then put the corn in an aerated bin, cool it and finish drying later.  You gained storage time by reducing the moisture.

In 2009, we had significant amounts of corn left in the field due to high moisture and insufficient drying capacity.  The corn reached about 18% moisture, which was the long term equilibrium for winter air in Iowa.   There were some mold issues, but not from fungi that produce mycotoxins.  Test weights remained about the same as they were in the fall, which suggested that there was not large dry matter deterioration.  Stalk lodging and snow cause field loss to the ground, which is a risk with leaving corn in the field.

The abnormally early cold temperatures are providing a significant benefit this year, in the holding of higher than normal moisture corn until it can be dried or used.


Charles Hurburgh Professor, Agricultural and Biosystems Engineering

Dr. Charles R. Hurburgh, Charlie to most everyone, is a native Iowan from Rockwell City (Iowa, USA). He continues to operate the family farm, and is a professor of Agricultural and Biosystems Engineering at Iowa State University. He has a bachelor's degree, master's degree, and doctoral degree fr...