Post-Harvest Grain Management Strategies For The Fall

Harvest is already underway in the Midwest with 22% of corn and 30% of soybean already harvested in Indiana by October 4 according to USDA-NASS crop progress report (USDA, 2020). It appears that the yields this year would be fairly good and farmers would be bringing in a good crop. This article focuses on securing the crop by ensuring that grain is harvested timely, dried adequately and binned correctly.

 

grain bins

 

Harvest grain timely and dry adequately for safe storage

First of all, it is important to know what moisture content you need to be storing your grain at based on your short and long-term marketing plans. How long you intend to store your grain will determine the level of moisture content to dry your grain to. Table 1 provides a guideline on recommended maximum moisture contents at storage periods from up to 6 months to over one year for various grain types. Note that the longer you intend to hold your grain, the lower the level of moisture you need to be. This is very important especially if you would be storing your grain through the warm summer months, when managing grain becomes more challenging, and the potential for insect pests and mold problems increases. Please note the caveat below the table headline – reduce safe storage moisture content by 1% for poor quality grain.

 

Table 1. Maximum moisture contents for grain harvest and safe storage recommended in the Midwest. (Source: Grain Drying, Handling and Storage handbook, third edition, MWPS-13).

Values for good quality, clean grain and aerated storage. Reduce safe storage moisture content by 1% for poor quality grain.

Maximum Moisture Content, %wb
Storage Period
Grain Type At Harvest Up To 6 Months* 6-12 Months** >1 Year**
Shelled corn and grain sorghum 30 15 13 13
Soybeans 18 13 12 11
Wheat, barley and oats 20 14 13 12
Flaxseed 15 9 7 7
Canola 14 9 8 8
Sunflower 17 10 8 8
Edible beans 16 16 13 13
*Up to 6 months from harvest refers to storage under winter conditions.
**6-12 months and >1 year storage refers to storage into the warm summer months.

 

Harvesting grain timely after it matures on the field is important for ensuring the yields achieved is secured in the bin. Moisture content is one variable that drives the decision on when to harvest because it impacts the cost that would be incurred in artificially drying grain using a low-temperature or high-temperature dryer compared to leaving the grain to naturally dry-down on the field. Table 1 gives maximum recommended moisture for various grains and oilseeds at harvest. Most farmers will typically take advantage of good dry weather to allow corn and soybean to naturally dry-down on the field to below 25% and 15%, respectively, before they commence harvesting. However, since field dry-down is weather dependent, some years happen to be great for fall field drying, while others are not. There are other risks, which determine whether to harvest early such as an extreme weather event like a storm that could cause huge damages to crops. The risks/cost of leaving the crop on the field to dry-down rather than harvesting early and drying artificially needs to be considered. Also, the rate of field dry-down for grain reduces as day-time temperature drops as we progress into the fall. So for corn planted late that would be harvested late in the fall, there is only a little window to take advantage of field dry-down. Additionally, make sure combine harvesters are adjusted to bring in clean grain, which helps grain handling through drying and storage. Excessive thrash/pods harvested with corn/soybean are a potential fire hazard when drying using high-temperature dryers, especially when thrash is allowed to accumulate in dryers. Routine cleaning of thrash from grain dryers is adviced (for example weekly).

Drying and cooling grain

Natural air (NA) or low temperature (LT) air (aeration with the addition of heat, 5 to 10oF) in-bin drying is recommended if corn and soybean are harvested below 20% and 15% moistures, respectively, especially when harvested early in the fall when ambient daytime temperatures are still in the 60 to 70oF range. Otherwise, consider using a high temperature dryer (180oF or more air temperature), especially for higher moistures so that grain is dried as quickly as possible to prevent the onset of spoilage in a wet holding bin. Shallower grain fill depths or larger diameter bins favor in-bin drying because the drying front has less depth to move through compared to a narrower and taller bin. Having adequate airflow (cfm/bu) by properly using an adequately sized fan is key to successfully using NA/LT systems for drying as well as for aeration. The higher the airflow, the better the system. An airflow of 1.5 cfm/bu is recommended for use in NA/LT in-bin systems for grain in Indiana.  For soybean, care needs to be taken to dry in order to prevent split beans. Ensure that drying air humidity levels are not below 40% when drying soybean with medium (120-140oF) or high-temperatures (160-180oF).

For both corn and soybean, ensure that adequate aeration is applied to grain using natural air after drying. Aeration is not intended for drying grain, but rather for lowering grain temperature (cooling) in order to prevent spoilage. Neverthless, a little bit of moisture is removed from the grain during each aeration cycle (about 0.25 to 0.3 percentage points of moisture  per 10oF temperature decrease).  Airflow rates as low as 0.05 (1/20) cfm/bu to over 1 cfm/bu can be successfully used to cool down grain in the bin. In general, dividing 15 by the airflow rate gives an estimate of the hours required to change the temperature of the grain by aeration. For example, it’ll take 150 hours of fan run time to change the temperature of corn having an airflow rate of 0.1 cfm/bu, and doubling the airflow rate to 0.2cfm/bu reduces the fan runtime by half (75 hours).  The cold winter ambient temperatures provide a natural low cost means to preserve grain by chilling. Chilled grain can be held cold through the spring.  Table 2 provides a guide on how to cool grain in step-wise phases through the fall-winter period. Dry binned grain can be cooled to below 32oF without any detrimental effects to the kernel integrity. Under cold grain conditions, insect pests are adequately controlled and in most cases killed during this period. Notice that grain should not be warmed up in the spring to ambient spring temperatures, but rather still kept cool. Additionally, during the warm spring period, the aeration fan’s airflow intake should be covered to prevent warm air from re-warming the grain through the plenum. Should the grain in the bin still be cold during the time of loadout from the bin, it is advisable to warm up the grain to the ambient temperature prior to load out. This will prevent moisture from condensing on cold grain during loadout. Having temperature cables in the grain bulk, and or temperature/relative humidity (RH) sensors in the headspace and/or plenum depending on whether you have a positive pressure aeration system (pushing air from the plenum through grain) or a negative pressure aeration systems (pulling air from the headspace through grain) will enable the temperature front be monitored as it moves through the grain. The use of temperature/RH sensors is a good way to monitor the progress of the temperature front during aeration so that fans can be shut-off timely, and therefore energy used wisely.

 

Table 2. Recommended aeration phases after drying grain in the fall.
Aeration Phases After Drying Grain
Phase 1: Fall Cool Down
– Lower grain temperatures step wise
• October – 40-45°F
• November – 35-40°F

• December – 28-35°F
Prevent re-warming grain during warm weather spells. Keep grain temperatures as low as possible.
Phase 2: Winter Maintenance
– Maintain low temperatures with intermittent aeration: January, February – 28-35°F
Prevent re-warming grain during warm weather spells. Keep grain temperatures as low as possible.
Phase 3: Spring Holding
– Keep grain cold from winter aeration
• Seal fans
• Ventilate only headspace intermittently
If grain in bin is cooler than the ambient, warm up grain to the ambient prior to load-out

 

Remove fines from the grain bulk core to facilitate aeration

Last but not the least is coring the bin during filling to prevent the accumulation of fines and brokens at the center of the grain mass, which could cause the onset of spoilage. Coring reduces the levels of fines and broken kernels, which lodge at the center of the bin during filling, and helps improve airflow through the grain bulk. A rule of thumb when coring a bin is to pull out 1/3 to 1/2 the bin diameter, so that you have an inverted cone at the surface (See Figure 1).

 

Figure 1. An illustration of a cored bin after the fines and broken corn has been pulled from the center, enabling better airflow during aeration (Figure is courtesy of Dr. Sam McNeill, University of Kentucky).

Figure 1. An illustration of a cored bin after the fines and broken corn has been pulled from the center, enabling better airflow during aeration (Figure Credit: Dr. Sam McNeill, University of Kentucky).

 

Ensure moisture meters used on the farm are calibrated prior to use. It is advisable to check your moisture meter calibration with the elevator you deliver grain to. This way ensures that the moisture content measured by your elevator when you deliver grain is close to what you would have measured prior to delivery. While you go about your harvest and work around your bins, remember to put safety first. Safety for your personnel and family members must never be compromised. In the busyness of the harvest season, remember to pause to think about whether you are going about your operations in a safe manner. Be safe!

 References:

MWPS-13 Grain Drying, Handling and Storage Handbook, 2017. Third Edition Copyrigt @ 2017, Iowa State University/Midwest Plan Service.

USDA, 2020. Crop progress report. USDA-NASS report relaesd on October 5, 2020. ISSN: 1948-3007. Access online on October 7, 2020 at https://downloads.usda.library.cornell.edu/usda-esmis/files/8336h188j/gx41n7114/rr172n08t/prog4120.pdf

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