Soybeans: Harvest and Storage

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Pub 811: Agronomy Guide > Soybeans > Harvest and Storage

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Minimize Harvest Losses

Soybeans are direct combined, preferably with a combine equipped with a floating flexible cutterbar and automatic header height control. Soybeans can be harvested at moisture levels below 20%, but they must be stored at 14% moisture or lower.

Harvest losses and mechanical damage may be high when soybeans are harvested below 12% moisture. A loss of just 4 beans/900 cm2 (4/ft2) represents an overall loss of 67 kg/ha (1 bu/acre). Losses can be minimized if a ground speed of 4-5 km/h is maintained. The reel speed should be adjusted to match crop conditions.

A floating cutterbar can be used to cut the soybean plants off, closer to ground level. Adjust the cleaning fan to provide maximum air without blowing soybeans into the return elevator or out the back end. Adjust the chaffer to allow the fan to separate pods and stalk pieces from the soybeans. Adjust the sieve to allow only soybeans through. Adjust the air speed, chaffer and seive settings throughout the day as the weather conditions and soybeans change.

Header maintenance is important. The majority of soybean losses occur at the header. The cutter bar must be sharp, and the knife sections must make good contact with the guard ledger plates to allow quick cutting action and rapid movement of the cut beans into the header. Add belting to the bat reel, or use an air reel to get short beans into the feed auger quickly.

If soybean plants remain standing and uncut behind the header:

• check blades and guards
• consider reducing ground speed

Quality and Identity Preservation (IP)

Preharvest

If the soybean crop is destined for an identity-preserved (IP) market, make a special effort to maintain seed quality. Staining and mechanical damage are the main problems at harvest that can downgrade quality. Mechanical damage can result in an entire load being rejected. Staining can occur from weeds, immature beans, dirt and dust. Prior to harvest, thoroughly clean combines, trucks, wagons and other handling equipment and bins to prevent contamination. Scout and rogue fields for off-types and other volunteer crops (e.g., corn). Check fencerows and roadsides for glass, metal, fence posts and other trash. Harvesting of IP beans must wait until soybean stems and weeds have dried down completely to avoid green staining of the seed. Remove weeds such as Eastern black nightshade and American pokeweed from the field before harvest, or have the combine operator avoid weed-infested areas.

Harvest and Storage

When harvesting IP beans that are a different variety from the previous field harvested, it is best to thoroughly clean out the combine from top to bottom to remove trapped beans. An alternative, although less-effective, method of combine cleaning involves combining a small area of IP beans separately and loading them into a "slush" wagon. The sample can be used to check moisture and combine set-up. Other harvest tips include:

• Oversee custom harvesters to make sure their equipment is ready to harvest.
• Keep a copy of the IP contract on hand to determine the quality parameters at harvest. IP harvesting starts later and ends sooner in the day than for commercial beans, mainly to prevent staining. Once contaminated, a combine is difficult to clean.
• It is best to harvest at moisture levels close to 14% to avoid the need for anything other than ambient air drying. Harvesting at or above 12% moisture, and gentle handling, are necessary to avoid cracked seed coats.
• Adjust the combine to varying harvest conditions throughout the day. Adjustments to reduce mechanical damage may increase dockage (pick) but are more than compensated for by premiums.
• Store IP soybeans in separate bins that are free of other soybean varieties and other grains and oilseeds.

If the crop was produced under contract, all of these requirements will be outlined in the signed agreement. With or without a contract, failure to comply can result in lost premiums.

Soybean Drying

Grain Dryers

The three basic general types of grain dryers used on the farm are:

• in-bin
• batch
• continuous flow

These three broad groups of crop driers can be further broken down into different types. No single drying system is superior to all others in every respect. System selection is dependent on desired features. These features include drying capacity, grain quality, fuel/drying efficiency (BTU/lb of water removed), convenience, manpower required to run the dryer, ability to dry a variety of crops, maintenance required and capital cost.

All dryers move heated air past the grain to evaporate moisture from the grain and carry the water vapour away. Heat is added to this drying air to reduce its relative humidity, thereby increasing its ability to pick up moisture. Wet grain can be dried at higher temperatures since it will be cooled as the moisture evaporates from the kernels. As the grain dries, it will approach the temperature of the drying air. The longer the grain kernels are in contact with this heated air, the drier and hotter the kernels will get.

Drying Soybeans With Heated and Unheated Air

Soybeans are sometimes harvested at a higher moisture content due to wet weather or are harvested earlier than expected to reduce combine losses. All drying methods are adaptable to soybeans with some restrictions on the use of heat and handling practices.

Take care when using heated air to dry soybeans that are higher in moisture than desired for safe, long-term storage. The relative humidity of the drying air must be kept above 40% to prevent seed coats from splitting. Experience has shown that with as little as 5 minutes exposure to high heat, it is possible to cause 100% of the soybeans to crack. Most recommendations for drying commercial soybeans suggest a maximum temperature of 55°C-60°C. In good drying weather, you may need to reduce this drying temperature to control seed coat cracking. Check the number of split seeds before and after drying to gauge the drying effect
.
Seed soybeans should be dried at temperatures below 40°C. This should only be attempted after several years of experience. Some seed companies frown on the use of any heat in conditioning seed soybeans. Ask your seed company what method of conditioning it allows or prefers for seed beans.

With bin dryers, use caution in any system that involves moving the soybeans in the bin with re-circulators or stirrators. Damage from handling can be severe, especially as the moisture content drops to 12%.

Natural-Air Drying

Tough soybeans can be dried with natural air under good drying conditions. Natural-air drying of soybeans requires careful management by the operator, since soybeans give up and take on moisture easily. The fan must be run only when the outside conditions will result in drying progress. Do not run the fan continuously, night and day, as re-wetting will occur at night, reversing any progress made during the day.

Minimum Requirements for Natural-Air Drying Soybeans

• full aeration floor in the bin
• level soybean surface across the whole bin
• minimum airflow of 6.5 L/sec/m3 (0.5 CFM/bu), preferably more
• clean beans with no pods or fines accumulations
• accurate moisture reading of the beans in the bin
• accurate outside air temperature and relative humidity measurement
• an understanding of soybean equilibrium moisture content
• an on/off switch for the fan

A full aeration floor is essential to move air uniformly through the entire bin contents. With a partial aeration floor or air duct system, dead areas will exist, leading to potential spoilage problems. Bean pods, trash and fines accumulations in the bin will restrict or divert airflow. Air moving through the bean mass will take the path of least resistance.

Determining Airflow

Sufficient airflow is needed to move drying air through the whole bean mass. To remove moisture, the minimum airflow required is 6.5 L/sec/m3 (0.5 CFM/bu). Anything less will only change temperature but will not change moisture content of soybeans. Higher airflow rates of 26 L/sec/m3 (2 CFM/bu) or greater, only get the job done quicker. In order to determine the CFM/bu value for a bin, determine the number of bushels in the bin and the static pressure that the fan is operating against. A simple manometer connected to the air plenum below the perforated floor will display the static pressure in inches of water column (see Figure 11-1, Home-Built Manometer). Determine fan output at the measured static pressure by using the fan performance curve. Divide the CFM output of the fan by the number of bushels in the bin to give the CFM/bu airflow. One strategy to get adequate airflow is to only partially fill the bin. This way, the fan will be operating at less static pressure and deliver higher airflow rates per bushel.

Equilibrium Moisture Content

Researchers have developed equilibrium moisture content tables that aid in predicting the final moisture content of soybeans when exposed to air at a certain temperature and relative humidity (see Table 2-18, Equilibrium Moisture Content (% Wet Basis) for Soybeans Exposed to Air). To determine, for example, the equilibrium moisture content of soybeans exposed to outside air at 10°C and 70% relative humidity, find the point at which the 10°C row and the 70% relative humidity column intersect. This point will be the equilibrium moisture content for soybeans. Given enough time, the soybeans will dry down to 13.2% moisture content.

Measuring Relative Humidity

Accurately measuring the relative humidity of the outside air presents a bit of a challenge. In some cases, this reading can be obtained from a nearby weather station. It is important to determine if a nearby weather station is an accurate reflection of conditions at a specific location. To air-dry soybeans, it is important to know the accurate relative humidity of the outside air. Household hygrometers tend to be inaccurate and are not recommended for measuring relative humidity when air-drying tough beans. A sling psychrometer or a good quality hygrometer are recommended for this purpose.

When to Run the Fan

Fan operation is not limited by the time of day but rather by air temperature and relative humidity levels. On some days, drying can be accomplished from 9 AM until midnight, while on others it may only be from 9 AM to 6 PM. Check the temperature and relative humidity of the air numerous times throughout the day. The outside air must be drier than the inside air for making drying progress. If the equilibrium moisture content on a given day is less than the moisture content of the wettest beans, drying is possible, and the fan should be on. Humidistats are available that will activate the fan at pre-set humidity levels. The operator can adjust the relative humidity level at which the fan is activated.

The beans at the top of the bin will be the last to dry. Each day of fan operation will push a drying front up through the bin. This drying front may not reach the top of the bin as quickly as expected. Be sure to take moisture samples at the same depth each time to know how the moisture content is changing at that depth. Bins with stirrators will have fairly uniform moisture levels throughout the whole bin.