By Dan Martens
University of Minnesota Extension
It’s time to take a close look at spring grain care, if you haven’t started already.
In 2013, a late spring led to wet soybeans and corn at harvest time; and propane supplies became short in the fall. Some soybeans and corn were not dried completely in the fall with the goal of keeping the crop cold and to finish drying in the spring. The cold winter makes a cold grain mass. Warmer, more humid spring weather can create condensation on the surface of the grain and on bin walls.
Most of the following discussion is from North Dakota State University Extension grain storage specialist Ken Hellevang and circulated in Minnesota by Regional Extension Educator Dave Nicolai.
The stored grain temperature increases in the spring due to an increase in outdoor temperatures and solar heat gain on the bin. Solar energy produces more than twice as much heat gain on the south wall of a bin in early spring as it does during the summer.
Periodically run aeration fans to keep the grain temperature below 30 degrees until the grain is dried if it exceeds recommended storage moisture levels; and below 40 degrees during the spring if it is dry. Grain should be checked every two weeks during the spring and summer for temperature, moisture, and any signs of spoilage or insect problems.
Check the moisture content of stored grain to determine if it needs to be dried. Adjust moisture meter readings for grain temperature based on the meter’s directions. Moisture measurements of grain at less than 40 degrees may not be accurate. Verify the accuracy of the measurement by warming the grain sample to room temperature in a sealed plastic bag before measuring the moisture content.
Corn should be dried to 13 to 14 percent moisture for summer storage. Soybeans should be dried to 11 percent, wheat 13 percent, barley 12 percent and oil sunflowers 8 percent.
Corn above 21 percent moisture should be dried in a high-temperature dryer because it can spoil faster than it dries with natural air drying at warmer temperatures. Corn might be stored safely at 22 percent moisture for about 190 days at 30 degrees; 60 days at 40 degrees; and only 30 days at 50 degrees. Light test weight, kernel damage, and foreign material reduce safe storage potential.
The cost of high-temperature drying per point of moisture removed using a moderately efficient dryer can be estimated by multiplying the propane price per gallon by 0.02. For example, the estimated cost per percentage point per bushel of drying with propane at $2.60 per gallon is 5 cents. To remove 8 points of moisture would cost about 40 cents per bushel for propane.
Obtain the most energy-efficient drying by operating the dryer at the highest temperature that will not damage the corn. For natural air-drying, assure that the airflow rate the fan supplies is at least 1 cubic foot per minute per bushel (cfm/bu) and the initial corn moisture does not exceed 21 percent.
Due to the higher propane price or lack of a high-temperature dryer, farmers may want to air-dry wetter corn. Corn at 23 percent moisture requires an airflow rate of at least 1.5 cfm/bu, which is not feasible in a full bin. If a bin is sized to provide an airflow rate of 1 cfm/bu, only fill the bin about three-fourths full to obtain an airflow rate of about 1.5 cfm/bu, which will permit air-drying corn at moisture contents up to 23 percent. For example, fill a bin to no more than 16 feet, rather than 22 feet.
The Minnesota Extension Publication for “Natural Air Corn Drying” offers these guidelines: 1) if the corn at the top of the bin is 19-21 percent moisture, run the fan continuously starting about March 15 until the corn is dry. 2) For 17 to 19 percent corn, run the fan continuously starting about April 1. 3) For corn less than 17 percent moisture, to dry to 14 percent or less, run the fan continuously starting about April 15. If you aim for 15 percent, turn the fan off during the warmest, driest weather or the corn will get too dry.
The goal is to get the grain dry before it warms up enough in the spring to start spoiling faster than you can get it dry. These dates are based on having average daily temperatures of about 40 degrees. We do need to make sure the grain stays cool until we are ready to get serious about drying it.
It can also be helpful to know that air at 50 percent relative humidity and 30 degrees can take corn moisture down to 13.9 percent; at 40 degrees down to 13.1 percent; at 50 degrees to 12.5 percent.
The goal is also to avoid over-drying the grain. Keeping grain below 40 degrees helps to reduce spoilage and insect development.