Soybeans: Harvest and Storage

Excerpt from 2002 edition of Agronomy Guide for Field Crops (Chapter 4)

Order 2009 edition of OMAFRA Publication 811: Agronomy Guide for Field Crops

Table of Contents

1. Minimize Harvest Losses
2. Quality and Identity Preservation
   • Preharvest
   • Harvest and Storage
3. Soybean Drying
   • Grain Dryers
   • Drying Soybeans With Heated and Unheated Air
   • Natural Air-Drying
   • Determining Airflow
   • Equilibrium Moisture Content
   • Equilibrium Moisture Content (% Wet Basis) for Soybeans Exposed to Air - Table 4-16
4. Updates on Soybeans: Harvest and Storage
5. Related links...

Minimize Harvest Losses

Soybeans are direct combined, preferably with a combine equipped with a floating flexible cutterbar and automatic header 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/ac). Losses can be minimized if a ground speed of 4-5 km/h (2.4-3 mph) is maintained. The reel speed should be adjusted to crop conditions.

A floating cutterbar can be used to cut the soybean plants off closer to ground level. The combine fan should be adjusted to provide maximum air without blowing soybeans into the return elevator or out the back. The chaffer is adjusted to allow the fan to separate pods and stalks from the soybeans and the sieve to allow only soybeans through. These settings should be adjusted as the conditions of weather and soybeans change.

Header maintenance is important. Blades and guards must be sharp-edged to provide a ledger plate allowing quick cutting action and rapid movement into the header. Belting on the bat reel to sweep the beans in and/or the addition of an air reel for short crops provides rapid movement into the combine.

The majority of the losses occur at the header.

If soybean plants remain standing and uncut behind the header:

• check blades and guards
• consider reducing ground speed

Quality and Identity Preservation

Preharvest

If the soybean crop is intended for an identity-preserved (IP) market, special effort must be taken to maintain seed quality. Staining and mechanical damage are the main problems at harvest. Staining can occur from weeds, immature beans, dirt and dust. Mechanical damage can result in an entire load being rejected. Prior to harvest, combines, trucks, wagons and other handling equipment and bins must be thoroughly cleaned 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, etc. Harvesting must wait until soybean stems and weeds have dried down completely to avoid green staining of the seed. Weeds such as Eastern black nightshade and American pokeweed may have to be removed from the field before harvest or avoided by the combine.

Harvest and Storage

If a different crop or variety was just harvested, harvest a small area separately to ensure the combine is clean. This sample can be used to check moisture and combine set-up. Oversee custom harvesters to make sure 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; otherwise staining will occur. 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, in addition to gentle handling, is necessary to avoid cracked seed coats. Adjust the combine to conditions throughout the day. Adjustments to reduce mechanical damage may increase dockage (pick) but is more than compensated for by premiums. IP soybeans should be stored in separate bins that are free from other soybean varieties and other grains and oilseeds. If the crop was produced under contract, many of these requirements may be outlined in the signed agreement. With or without a contract, failure to comply can result in lost premiums.

It is important to assess the quality of seed at harvest in order to make appropriate adjustments to the combining and seed-handling process to reduce further damage to the seed. See Figure 4-3, Hypochlorite Soak Test for Soybeans, for a discussion of soybean seed coat damage.

Hypochlorite Soak Test for Soybeans

Introduction
The soak test is a quick test to reveal soybean seed coat damage. The test is primarily used during harvest to help reduce mechanical damage due to combining and seed handling. Samples are tested in the field, and the appropriate adjustments are made to reduce damage to less than 10% damaged seeds. The test is also useful in determining processes that cause damage within the conditioning plant.

Procedures

1. Prepare a 1:5 dilution of household bleach to water to obtain a 1% sodium hypochlorite solution. Note: Dilutions as low as 1:43 have been used.
2. Obtain several shallow plastic containers (similar to petri dishes) that will each hold 100 soybean seeds.
3. Take a random sample of seed. Count out four replicates of 100 seeds each, excluding splits and other obviously broken seeds. Place in plastic container. Note: A counting board can be made by drilling 100 quarter-inch holes in a 6.5 x .25 x 0.5 in. board.
4. Submerge each 100-seed replicate in the solution for 10 minutes.
5. Remove swollen seeds with tweezers.
6. Average the number of swollen seeds per replicate. If over 10%, adjust the combine or handling to reduce damage.

Evaluation
Seeds can usually be separated into three different categories following the 10-minute soak.

1. Firm seeds do not take up solution. These are considered to have little or no damage.

2. Wrinkled seeds take up a small amount of solution, which causes their seed coats to blister. These are only very slightly damaged.

3. Swollen seeds take up solution and appear nearly two to three times their original size. Some may have only a large water blister at one end, and others may be breaking apart. These seeds are considered damaged.

Figure 4-3.
Hypochlorite Soak Test for Soybeans
Source: Iowa State University of Science and Technology - Seed Testing Laboratory, Seed Science Centre 1992

Soybean Drying

Grain Dryers | Drying Soybeans With Heated and Unheated Air | Natural Air-Drying | Determining Airflow | Equilibrium Moisture Content | Equilibrium Moisture Content (% Wet Basis) for Soybeans Exposed to Air - Table 4-16

Grain Dryers

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

1. in-bin
2. batch
3. continuous flow

These three broad groups 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 water removed), convenience, manpower required to run the dryer, ability to dry a variety of crops, maintenance required and capital cost.

All dryers move 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 earlier than expected to reduce losses. All drying methods are adaptable to soybeans with some restrictions on the use of heat and handling practices.

Care must be taken when using heated air to dry tough soybeans - beans 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 five 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 (131°F-140°F). 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 (104°F). 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 tough seed beans it prefers.
With bin dryers, caution should be used in any system that involves moving the soybeans in the bin with recirculators or stirrators. Damage from handling can be severe, especially as the moisture content drops to 12%.

Natural-Air Drying

Do not run the fan continuously, night and day, as you will re-wet the soybeans at night. The progress you make during the daytime will be undone at night. Careful management of fan operation is critical for drying success.

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 both give up and take on moisture easily. The fan must be run only when the outside conditions will result in drying progress.

Minimum Requirements for Natural-Air Drying

• 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 whole 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 than 6.5 L/sec/m3 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 gets the job done quicker. In order to determine the CFM/bu value for your 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 show you the static pressure in inches of water column (see Appendix I, Home-Built Manometer). Using your fan performance curve, you can find the fan output at the measured static pressure. Dividing the CFM output of the fan by the number of bushels in the bin will give you your CFM/bu airflow. If you cannot get adequate airflow, one strategy 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 4-16, 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 (50°F) and 70% relative humidity, find the point at which the 10°C (50°F) row and the 70% relative humidity column intersect. This point will be the equilibrium moisture content for soybeans at the outside air conditions stated. 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 this weather station is an accurate reflection of conditions at your location. To air-dry soybeans, you need to know, with accuracy, the relative humidity of the outside air. Do not use your household hygrometer to measure relative humidity for air-drying tough beans. These units tend to be inaccurate. It is recommended that you purchase a sling psychrometer or a good quality hygrometer for around $100.

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 9:00 am until midnight, while on others it may only be from 9:00 am to 6:00 pm. Check the temperature and relative humidity of the air numerous times throughout the day. The outside air needs to 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 your 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.

Updates on Soybeans: Harvest and Storage

No updates available at this time.

Related links...

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