Posted 27 March 2012. Crop Management.
Unusually Warm Spring May Cause Stored Grain Problems
Grain storability depends on grain quality, moisture content and temperature
Source: North Dakota State University Press Release. www.ndsu.nodak.edu
Fargo, North Dakota (March 19, 2012)--The warm spring temperatures following a warm winter may lead to stored grain problems, particularly for grain that exceeds the recommended storage moisture content or did not stay cool during the winter.
The storability of grain depends on the grain quality, moisture content and temperature, says Ken Hellevang, the North Dakota State University Extension Service’s grain drying expert.
Grain moisture content must decrease as the grain temperature increases to store grain safely. For example, the allowable storage time of 17 percent moisture corn is about 280 days at 40 degrees, 75 days at 60 degrees and only 20 days at 80 degrees. Even 15 percent moisture corn has an allowable storage time of only about 70 days at 80 degrees.
Allowable storage time (AST) is cumulative, so because some of it was used last fall and during the winter, only a portion of the AST still remains. The goal should be to keep the grain as cool as possible, preferably below 40 degrees.
Due to the nice 2011 harvest season, some farmers only relied on field drying, and some corn was placed in the bin at moisture contents slightly above the recommended level for long-term storage. They either used or plan to use natural air-drying rather than drying the corn in a high-temperature dryer.
“This corn should be monitored and kept cool by running aeration fans at night or during times when outdoor temperatures are cooler than 40 degrees until the corn is dried,” Hellevang advises. “Because grain spoils faster at warm temperatures, air-drying when average air temperatures exceed 70 degrees may result in spoiled grain before it gets dry. Unfortunately, the rate of spoilage increases faster than the rate of drying at warmer temperatures.”
If fans were operated during the abnormally warm temperatures, continue to operate them to cool the grain. Average temperatures in the 50s or 60s are better when air-drying corn in the spring. The required airflow rate increases with warmer temperatures and moisture contents.
Stored grain temperature increases in the spring due to rising 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. Air temperatures in the bin head space will be much warmer than the outdoor air temperature, which will heat the grain near the top surface.
Grain should be kept cool during spring and summer storage, Hellevang says. Periodically run aeration fans to keep the grain temperature below 40 degrees during the spring.
He also recommends monitoring stored grain closely to detect any storage problems early. Grain temperature and moisture content should be checked every two weeks during the spring and summer. Grain should be examined for insect infestations as well.
Corn needs to be dried to 13 to 14 percent moisture for summer storage to prevent spoilage. Soybeans should be dried to 11 percent, wheat to 13 percent, barley to 12 percent and oil sunflowers to 8 percent for summer storage.
Check the moisture content of stored grain to determine if it needs to be dried. Verify that the moisture content measured by the meter has been adjusted for grain temperature. In addition, remember that moisture measurements of grain at temperatures below about 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.
Grain storage molds will grow and grain spoilage will occur in grain bags unless the grain is dry. Grain in the majority of the bag will be near average outdoor temperatures, so grain will deteriorate rapidly as outdoor temperatures increase unless it is at recommended summer storage moisture contents.
Corn at moisture contents exceeding 21 percent should be dried in a high-temperature dryer. For natural air-drying, assure that the airflow rate supplied by the fan is at least 1 cubic foot per minute per bushel (cfm/bu) or the recommended airflow rate for your climate. Also make sure the initial corn moisture does not exceed 21 percent.
Start drying when the outside air temperature averages about 40 degrees. Below that temperature, the moisture-holding capacity of the air is so small that very little drying occurs. Hellevang recommends an airflow rate of at least 1 cfm/bu to natural air-dry up to 16 percent moisture soybeans. The expected drying time with this airflow rate will be about 50 days.
He doesn’t recommend operating the drying fan just during the day when the air is warm and shutting it off at night because the warm daytime air normally dries the grain to moisture contents lower than desired. For example, air at 70 degrees and 40 percent relative humidity will dry corn to about 10 percent moisture. The grain above the drying zone will be warmer if the fan is run just during the warm portion of the day, which will cause the grain to deteriorate faster. And even though the warm air may hold more moisture, the drying time is still almost twice as long because the fan is operating only half of the day.
Natural air-drying oil sunflowers also should start when outdoor temperatures average about 40 degrees. Hellevang recommends an airflow rate of at least 0.75 cfm/bu to natural air-dry up to 16 percent moisture sunflowers.
He suggests an airflow rate of at least 0.75 cfm/bu to natural air-dry up to 17 percent moisture wheat. Start drying when the outside air temperature averages about 50 degrees. Drying during an average May is similar to drying wheat and barley during an average September.
Also use an airflow rate of at least 0.75 cfm/bu to natural air-dry up to 16 percent moisture barley. This is particularly important for malting barley in instances when germination can be lost.