It’s been a mostly dry and warm harvest with bins filling quickly with corn and soybeans on farms and at country elevators. With night-time temperature forecast ranging in the mid-30s to high-40s in the next ten days, the time is right to cool corn and soybeans but not necessarily to the same temperatures and ideally without excessive shrink. This article reviews some tools and best practices for cooling and storing corn and soybeans through the winter and into early spring.
Observed Corn and Soybean Quality
We have been receiving corn for drying and storing at the ISU Kent Feed Mill & Grain Science Complex (FMGSC) in Ames, Iowa, since early September. About 80,000 bu were received between 20-25% moisture content for a high-capacity dryer test. This provided an early glimpse on quality which overall has been good. Due to the impact of Southern Rust in many fields, corn plants shut down earlier in the season resulting in lower yields reflected in smaller kernels compared to normal and test weights about 2-3 lb/bu lower than normal. In terms of composition, starch content is somewhat lower and protein higher. On the other hand, corn is testing well below limits for six mycotoxins of concern and consistently grades No. 1 with less than 2% Broken Corn and Foreign Material (BCFM).
Soybeans have been harvested well below the 13% marketing moisture content. In much of Iowa, moisture content has ranged from 9-11% which represents a substantial moisture shrink and yield loss. Soybeans received at the FMGSC were between 9-9.5% and are in the process of being reconditioned in one of our higher airflow bins.
Tips for Cooling Corn versus Soybeans
A good decision-making tool for when to turn on aeration fans, how long to run them, and what temperature corn and soybeans will cool to is the ISU Grain Aeration & Storage App available free of charge for Android and I-phones. It allows for determination of the Equilibrium Moisture Content (EMC) and Safe Storage Moisture Content (SSMC) relationships for corn, soybeans and more than a dozen other crops as a function of ambient temperature and relative humidity. For example, the SSMC for soybeans at 50°F is 12.6%. Thus, if soybeans are below that moisture content, it would be a waste of electricity to run aeration fans to cool them below 50°F. Additionally, soybeans cooled to that level and maintained at that moisture content or below will store well into next spring and summer. In comparison, the SSMC of corn at 50°F is 14.3% which is 0.7 percentage points (PPTs) below its market moisture content of 15%. Thus, cooling corn into the mid-30s increases its potential storage time. The SSMC of corn is 14.8% at 40°F and 15.2% at 35°F.
Another important consideration when cooling corn and soybeans is the amount of moisture shrink caused by evaporative cooling. No matter the initial temperature or moisture content of soybeans, when aerated with air averaging 50°F and 60% RH, over time they will equilibrate to 11.2% moisture content. Thus, if soybeans range from 9-11% moisture content, they would gain some moisture while minimizing or avoiding additional shrink loss. In comparison, when aerated under the same conditions, corn will equilibrate to 13.3% moisture content. At 35°F and 60% relative humidity corn will equilibrate to 14.2% and at 40°F and 60% relative humidity to 13.6%. Thus, if corn is placed in storage between 14.5 to 15.5% moisture content, it would potentially shrink by as little as 0.3 to as high as 1.9 percentage points (PPTs) below the market moisture content. Given we transfer corn weekly to our feed mill, we aim to cool corn in our storage bins to 35-45°F and maintain moisture contents between 14-14.5% moisture content.
The Grain Aeration & Storage App includes an aeration weather forecast tool that will provide a recommended thermostat setting based on a location’s 6-day weather forecast. It will also provide the number of hours each day ambient temperature is projected to be at or below the thermostat setting. For example, based on this week’s Des Moines weather forecast, the recommended thermostat setting is 55°F at 50% fan operating time which would result in 14 to 24 hours of air available per day and a total of 120 hours to cool stored corn or soybeans below that temperature for the next six days. At a typical airflow rate of 0.1 CFM/bu, 120 hours is 80% of the hours needed to move a cooling front completely through a cored and un-peaked grain mass. Thus, a simple thermostat adjusted according to the App’s recommendation suffices to accomplish cooling of stored grain over a reasonable length of time. However, when soybeans are to be reconditioned or to minimize shrink loss during corn cooling, an automatic control system that operates fans based on temperature and relative humidity is preferred over older style thermostats and humidistats. Technology platforms such as the AGI Suretrack, Amber Ag ACE Air, OPI Blue, STIG Auto-Bin, or Sukup Synk systems are commercially available and highly recommended.
Coring and Un-peaking the Grain Mass
One of the inherent problems when filling a storage bin with corn or soybeans is the accumulation of denser fine material under the loading spout and lighter foreign material (such as cob pieces or bean pods) flowing toward the wall. The accumulation of fine material reduces porosity and increases resistance to airflow. Combined with a peaked grain mass, this causes non-uniform airflow and thus uneven cooling. This typically results in doubling or tripling of cooling times through the core and peak.
Thus, it is a best practice to core and unpeak a grain mass as soon after harvest as possible. At the FMGSC we started coring each of our bins soon after filling by removing enough corn until the BCFM content of transferred corn decreased to approximately the average initial level, i.e., 2% BCFM or less. Practically, this resulted in an inverted cone with a diameter of about half the diameter of the bin. Based on the progress of observed cooling fronts and comparing temperatures of the center versus periphery cables, further coring or additional leveling of the top grain surface was not necessary to achieve uniform cooling of the grain mass.
Final Thoughts
After the final cooling cycle in the fall, remember to cover fan inlets to keep cooled grain cold. At the FMGSC, we have self-closing shutters installed on each fan. This prevents cold air from seeping out of the bottom of the bin when headspace air above the grain surface warms and expands due to solar radiation. The day-night temperature change cycle in the headspace causes a push-pull cycle that is mitigated when fans are covered. While properly dried, cored, unpeaked, and cooled grain should store well through the winter and into next spring and summer, be sure to check stored grain regularly and ideally using carbon dioxide (CO2) monitoring (which will be the topic of a future article). Additional grain storage resources can be accessed here or contact your Extension Ag Engineer.
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- Professor, Agricultural and Biosystems Engineering
- Director, ISU Kent Feed Mill & Grain Science Complex