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.
- 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.
- 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.