By Delbert G. Voight
Over the last several years of working with what I consider the top soybean producers in Lebanon County I have learned the importance of timely harvest of soybeans. This week I noticed late group 2 beans were approaching harvest moisture. It has been my experience that once 95% of the pods turn brown, about a week later it is time to combine. Some recent work at Iowa State showed a 3.2% loss of moisture per day, more than 5 times that of corn. So dry down is quick. The data also suggested about 12 days after pod maturation 13% moisture was noted over the study period.
Once moistures dip below 13% a grower is essentially giving the mill soybean dry matter. since they will correct the moisture to 13%. I still remember John Yocum referring to the fact that after grain first reach harvestable moisture, dry matter losses occur simply by the alternating day night and heavy dew.
The Penn State Extension Crops Team conducted a planting date study at SEAREC with one soybean variety, one seeding rate, and different planting dates from March 28th to May 28th. It is important to consider the variety since some varieties will have slight differences in the pod integrity and not tend to split as the heavy dew at night can speed up this process. There are also impacts of erect varieties that might tend to dry quickly and delays in harvest may impact those versus varieties that that tend to lay over and nestle protecting large fluctuations in dry down.
Figure 1 shows the 2019 study at Landisville Research Station where the same variety was planted on 5 different dates. When the early planting was ready to be harvested, the soybeans on the left (planted two weeks earlier than the beans on the right) could be harvested two weeks before later plantings (Figure 1). If harvest was delayed as little as two weeks until the rest of the planting dates matured, a significant amount of soybeans would be lost to shattering.
Figure 1. Planting date study at Landisville Research Station
Numerous tests of soybean combine losses show that up to 12% of the soybean crop is lost during harvest. Harvesting losses cannot be reduced to zero, however they can be reduced to about 5%.
|Harvest Delay||% yield lost|
|% yield lost|
|% yield lost|
|% yield lost|
Table 1. Effect of harvest delay on soybean yield losses.
Adapted from the University of Wisconsin
Combines can be operated to reduce losses without affecting the harvesting rate. Consider shatter losses of 2% acceptable, and average losses are 5% or more.
If you assess the discount for bringing soybeans in a little wetter than normal there will be some cost drop the beans. In the following table you will note the relative cost per bushel of soybeans to be around 30 cents. This is a cost that is easily overcome by the reduced harvest loss in the field at current market prices. It appears that soybean dryer than 13% return about the same to management but this does not take into account the penalty of shatter loss in the field.
Table 2. Two discount Schedules for $10.00 Per Bushel Soybeans and the Weight/Value Lost From Soybeans at Moistures Other Than 13.5 % M.C. Standard
|Soybean Harvest Moisture, %,Wet Basis||Weight of Water Loss (+) or Gain (-), Lbs/Bu to Convert Soybeans to 13.5% Moisture||$.12 Discount Per Bushel Per Point of Moisture (2% Per Point of Moisture), $||($.12 Discount) Price Per Bushel, $||($.12 Discount) Value Per Bushel, $, Adjusted for Moisture||$.20 Discount Per Bushel Per Point of Moisture (3.3% Per Point of Moisture), $||($.20 Discount) Price Per Bushel, $||($.20 Discount) Value Per Bushel, $, Adjusted for Moisture|
|12||-1.5|| ||10.00||9.93|| ||10.00||9.93|
|11||-2.5|| ||10.00||9.86|| ||10.00||9.86|
|10||-3.5|| ||10.00||9.79|| ||10.00||9.79|
|9||-4.5|| ||10.00||9.72|| ||10.00||9.72|
|8||-5.5|| ||10.00||9.65|| ||10.00||9.65|
Tips for keeping combine losses low
There are combine heads that force air back into the platform to assist in reducing harvest as well as other types of heads. However, there are some simple rules to follow. I found the following excerpts from a Missouri article useful during harvest to capture the losses that may occur during harvest (Missouri Department of Agricultural Engineering).
Your best guide for correct combine adjustment is your operator’s manual.
Remember that more than 80 % of the machine loss usually occurs at the gathering unit. The height of the cutter bar directly impacts what beans get into the bin. If I were to harvest pods by hand versus as little as a 3.5 inch height of cut that would equate to a 5% loss just from the cutter bar height go to 5 inch height of cut and that jumps to 10% loss. The following suggestions will help keep these losses to a minimum.
- Make sure that knife sections, guards, wear plates and hold-down clips are in good condition and properly adjusted.
- Use a ground speed of 2.8 to 3.0 miles per hour. To determine ground speed, count the number of 3-foot steps taken in 20 seconds while walking beside the combine. Divide this number by 10 to get the ground speed in miles per hour.
- Use a reel speed about 25% faster than ground speed. For 42-inch-diameter reels, use a reel speed of 11 revolutions per minute for each 1-mile-per-hour ground speed.
- Reel axle should be 6 to 12 inches ahead of the cutter bar. Reel bats should leave beans just as they are cut. Reel depth should be just enough to control the beans.
- A six-bat reel will give more uniform feeding than a four-bat reel.
- Complete the harvest as quickly as possible after beans reach 15% moisture content.
- A pick-up type reel with pick-up guards on the cutter bar is recommended when beans are lodged and tangled.