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Soybean – Harvesting

Soybeans are one of the last pulse crops planted and harvested in most regions of Alberta. While environmental conditions are such that the yield potential of soybeans is much less than that of other regions in Canada, many are finding it a viable option for their rotations. Marketing of soybeans is rarely a challenge. Resistance to Aphanomyces and some other seedling root diseases are another appealing characteristic. Soybean acres in Alberta are predominantly herbicide tolerant varieties which simplifies weed control. As genetic advancement reduces the number of heat units required to successfully harvest a crop, soybeans could be come a profitable alternative pulse crop. 

Pre-Harvest Considerations

CROP MATURITY
  • The rapid shortening of days starting in mid-August drives the soybean to maturity.
  • Soybeans begin to mature as defoliation begins. Leaves begin to dry down and fall off the main stem, while pods turn brown and the seeds will rattle when fully mature.
  • At Stage R7 the soybeans reach physiological maturity and frost may reduce quality with green seed, but would have less than 10% impact on yield.  See Soybean Maturity Guide.
  • At Stage R8 soybeans reach full maturity, when 95% of the pods are brown. Seeds inside the pods will rattle and all the leaves will have dropped. 
  • At maturity, it is important to consider seed moisture to determine harvest time.

SEED MOISTURE CONTENT
  • Harvest timeliness is important, and while ideal moisture content for storage and harvest is 13%, soybean harvest can begin at seed moistures up to 20% as they do dry down well under aeration.
  • Delaying harvest until seed moisture is less than 13% can result in increased shatter loss, increase seed coat damage, or splits as well as yield (weight) loss.
  • Soybeans are considered dry at <14% seed moisture content; tough at 14.1% – 16% seed moisture content; and damp at 16.1% – 18% seed moisture content.

FIELD MONITORING
  • Pre-harvest field monitoring will help determine which harvest system to consider, if more than one is available, and will greatly assist in determining when to begin harvest operations.
  • Monitoring fields means checking plants in numerous locations for uniformity of stages of maturity.
  • Most fields will not be 100% uniform in topography – there could be greener conditions in lower, wetter areas and further advanced plants on higher areas.
  • A decision to begin harvest will hinge on a majority of the field meeting certain criteria. Do not sacrifice the quantity and quality of your crop waiting for smaller greener areas to reach the proper stage to start harvest.
  • If stems or leaves remain green and tough, do not delay harvest until green stems mature if seed moisture is ideal. Time harvest to avoid a hot afternoon when soybeans will be at their driest and are most sensitive to mechanical damage.
  • Minimum temperatures for soybean seed ripening has been shown to be 8°C to 9°C with the optimum temperature being 19°C to 20°C.
  • Cool temperatures (less than 10°C) during seed fill can negatively affect soybean yield by reducing seed size and delaying maturity. 
  • Soybeans are susceptible to frost in early fall. A light frost of 0°C to -1°C may kill top leaf growth, but should not affect pods and seeds.
  • Temperatures below -1°C for an extended period of time can cause damage to green stems, pods, and seeds, reducing yield and quality.
  • Soybeans are most susceptible in the reproductive (R) 5 to R6 stage. In R6 stage (full seed), plants are still green and top nodes are still filling. At this stage frost may reduce yield by up to 50%.
  • In the R6.5 stage, when seeds have finished filling at the top of the plant and bottom leaves are starting to drop but pods are still green/yellow, frost damage could reduce yields by up to 30%.
  • Harvesting too early will result in immature seeds – this is especially important with yellow cotyledon varieties because immature yellow-green seeds will result in downgrading.
  • Harvesting too late when the pods are dry and brittle may result in shatter losses and will increase the risk of poorer quality seed due to adverse weather.
  • The decision to start the harvest process will depend on three factors: 
    • crop maturity (stage of uniformity – how variable is the crop’s maturity?);
    • seed moisture content; and
    • presence of weed growth.
  • Other considerations may include weather patterns, and marketing considerations (for human consumption, livestock feed or seed).

PRESENCE OF WEED CONTROL
  • Waiting for green weed growth to drydown will jeopardize quality and yields.
  • Swathed green weeds are unlikely to dry sufficiently in a few days, so combining will be delayed.
  • Green weed material in a straight-cut operation will cause extra wetness in the threshing areas of the combine, resulting in moisture on the seed coat and dirt adhering to this moisture (earth tag).  Grades will be lowered because of earth tag (see Grading Section).

PRE-HARVEST AIDS (GLYPHOSATE)
  • There are various registered harvest aid herbicide products for soybeans. 
  • If using a pre-harvest herbicide for weed control, ensure that the weeds are at the correct stage and are actively growing for best product performance. 
  • Make sure to select the right product, follow label directions, and timing of application. Harvest aid products vary in speed of activity, efficacy, and pre-harvest intervals.
  • In conventional varieties, pre-harvest glyphosate must only be applied when the grain moisture content is less than 30% in the least mature part of the field to prevent unacceptable residues in the harvested grains. The crop will have lost 80% – 90% of leaves, and 80% of the pods are yellow.

KEEP IT CLEAN
  • Certain crop protection products can restrict the marketing options for your pulse crop. Before you make your crop management plans, talk to your grain buyer and read the Keep it Clean Pulse Maximum Residue Limits Advisory for a list of products of concern for this year, and the steps you can take to mitigate risk.
  • More than 85% of Canada’s pulse production is exported to feed the world. Market access is important to the Canadian pulse industry, and growers play a key role in keeping the doors open.
  • Source: For the latest “Keep it Clean” updates, visit Keep it Clean.

Harvest Systems

Soybeans Being Unloaded from the Combine into a Truck

COMBINING
  • Soybeans are most commonly straight cut. 
  • Harvesting can begin at 20% moisture content. Harvesting at higher moisture content can help to reduce seed damage and downgrading. However, grain must then be dried and conditional to safe moisture content after harvest.
  • Seed damage is high when soybeans are harvested at less than 12% moisture, and harvest losses can also be high under dry conditions.
  • Swathing soybeans is not recommended due to increased risk of shattering losses. As well, soybeans have very little plant material to create a swath and little stubble to act as an anchor.
  • Therefore, swaths would be susceptible to movement by wind and pick-up could be difficult, because swathing increases shattering losses, and swaths are prone to blowing, as there is not much stubble to anchor them.
  • The majority of soybean seed loss at harvest occurs at the cutter bar. Floating cutterbars can be helpful to reduce losses as well as cutting as close to the ground as possible will help capture low pods. Consider the use of a flex header to help reduce losses.
  • Soybeans should be handled gently at harvest. The seed coat of soybeans is susceptible to mechanical damage and the drier the soybeans, the more prone they are to splits.
  • Using conveyors and avoiding over handling can also help avoid cracking and damaging the seeds, which can result in increased dockage.

COMBINE SETTINGS
  • Start with the combine manual and use the suggested settings.
  • Adjust the cutter bar to cut as low as possible, but still allow it to float on the ground. Straw must be mature – otherwise too many pods remain unthreshed.
  • Concave clearance and cylinder speed should be set to avoid seed cracking.
  • Feed uniformly at a speed to minimize losses. 
  • Only marginally slowing down may result in a significant decrease in seed loss.
  • Studies have shown that yield loss increases with increased harvest speed. Speeds of over four miles per hour (6.4 kilometres per hour) have been shown to increase the risk of harvest loss. At 2, 3 and 4 mph, the header losses were calculated at about 1.36 bu/ac but at 5 mph the header losses nearly doubled, to 2.18 bu/ac. 
  • Over threshing can be seen in cracked seed, which can also be a result of going too slow. In pulses where cracked seed can be a downgrading factor, a balance between over threshing and seed loss should be considered.
  • Adjust fan speed to the point where seed is just beginning to blow over. Open chaffer and sieve settings as wide as you can tolerate
  • Feed the combine properly. Uneven windrows or feeding during straight cutting can result in higher losses. Conventional combines with walkers thresh and separate the grain best when a wider swath is fed evenly into the width of the cylinder and walkers. Rotary combines perform better with a narrow windrow.
  • PAMI research found that when a windrow was concentrated down the middle of a conventional combine, losses were 7.5%, rising to 12.3% when the bulk was on one side of the combine. For a uniform crop fed evenly into the combine, losses were just 2.2%. The reason is that for uneven feeding, air cannot move through the straw and grain is moved out the back of the combine.
  • Air reels:  Air reels may help to keep the knife cleaner than standard bat or pick-up reel-type headers. A study by PAMI found that by adding an air reel reduced losses by more than half when compared to losses recorded using an auger header and pick-up reel.

NO DESICCATION
  • Soybeans do not require desiccation as they are able to dry down nicely as they mature.
  • Yield and quality are maximized if soybeans are left to mature naturally in the field. If green, weedy material is a concern in the field, there are a number of registered pre-harvest products that can be used on soybeans.

MANAGING LOSSES
  • Measure what your losses are. 
  • The use of a drop pan is recommended as combine loss monitors are not always accurate or properly calibrated.
  • Checking for losses on the ground is important (only four beans per square foot on the ground equals 1 bu/ac of yield).
  • Adjustments should focus on gathering at the header area as that accounts for more than 80% of the harvest loss. Loss should ideally be less than 5% of the total yield.
  • Pods that never make it into the combine can account for a large amount of harvest loss. These losses occur because of lost pods at the header, either shattering or left below the cutter height. Header losses can be minimized through good management practices such as proper field selection, crop rotation, and rolling fields to allow combine header to operate close to the ground.
  • Combine and equipment adjustments play a significant role in reducing soybean harvest losses. The operator should stop the combine periodically and check the amount and type of loss that is occurring.
  • Types of potential losses include shatter loss, loose stalk loss, lodged stalk loss and stubble loss.
  • For further information on how to measure losses, refer to Michigan State University, Measuring Soybean Harvest Losses.

Soybean Straw Management

Western Canadian research into the nutritive levels and value of soybean straw is limited, but it is believed that soybean straw has considerable nutrient value when used as an alternative feed source and as a nutrient when returned to the soil.

BENEFITS OF LEAVING SOYBEAN STRAW ON THE FIELD 
  • One of the benefits from growing a soybean crop is the positive effect of residue in the soil. Soybean straw contains nutrients, which once broken down by the soil micro-flora, can be made available to the following year’s crops.
  • Improved soil structure, tilth and recycled nitrogen for succeeding crops are all benefits of soybean straw incorporation. In fact, most of the nitrogen returned to the soil after growing a soybean crop comes from the straw.
  • Because of these benefits, it is recommended that soybean straw remain on the field and not be baled off for feed purposes. Consider the following:
    • Soybean straw breaks up and pulverizes quite readily when combined.
    • Soybean straw that is slightly green or tough will remain almost whole going through the combine.
    • A good straw chopper and chaff spreader will cut and spread the straw and chaff sufficiently so that tillage or direct seeding is not a problem.
    • Tough straw will wrap around the chopper drum if the straw chopper knives are dull and worn.
  • The decision to work straw back into the soil or bale and feed it is entirely up to each individual operation. It’s important to recognize soybean straw’s worth and not under-value it.

VALUE AS A FEED SOURCE
  • When assessing the benefits of baling versus incorporating these nutrients into the soil, the cost of baling straw and hauling it must be taken into consideration.
  • Overall quality is usually better than cereal straw. Soybean straw can be significantly higher in protein, but high fibre levels limit digestibility and expected feed intake.
  • Soybean straw is primarily useful for beef cattle rations where high quality roughage is not as important as for other classes of livestock – when soybean straw is fed with higher quality roughage and/or grain, it can produce a very cost-effective ration (the higher protein levels generally make soybean straw a better match with grain than cereal straw).
  • Palatability studies (how well an animal will consume the feed) with soybean straw have not been conducted – anecdotal evidence with beef cattle suggest a wide range in soybean straw palatability (cattle devouring the feedstuff versus complete rejection).
  • Processing the straw (such as grinding or chopping it with machines like mix mills or hay busters) and mixing the straw with other feeds may help with palatability.
  • Farmers thinking of removing soybean straw should test it for protein, phosphorus, potassium and sulphur to determine the nutrient content. A feed analysis of a representative sample of soybean straw for protein, phosphorus, potassium and sulphur is needed to do the calculations on value of selling as feed versus improving your soil.

RESOURCES

LINKS

Special thanks to Saskatchewan Pulse Growers and Manitoba Pulse and Soybean Growers.