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 beginning to turn and in some shale areas were already a mature brown coloration. It has been my experience that once 95% of the pods turn brown about a week later it’s 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. For more information visit Iowa State University, How Fast do Soybeans Dry Down in the Field?
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 the plants first reach harvestable moistures, dry matter losses occur simply by the alternating day/night and heavy dew.
Figure 1. This picture was taken from our Landisville Research Station where the same variety was planted on 5 different planting dates when the early planting was ready to combine the soybeans on the left (planted two weeks earlier than the beans on the right) could be harvested two weeks before later plantings. If harvest had been delayed as little as two weeks on all plots, until the rest of the planting dates matured, there would be a significant amount of soybeans lost from shatter losses. Image Credit: Del Voight
Numerous tests of soybean combine losses show that up to 12 percent of the soybean crop is lost during harvest (Table 1). Harvesting losses cannot be reduced to zero, but they can be reduced to about 5 percent. Combines can be operated to reduce losses without affecting the harvesting rate. This guide describes the major sources of loss. Consider shatter losses of 2 percent acceptable. Average losses are 5 percent or more.
Table 1. Effect of harvest delay on soybean field losses in % yield lost
|Harvest Delay||Year 1||Year 2||Year 3||3-year Average|
Source: University of Wisconsin
If you assess the discount for bringing soybeans in a little wetter than normal there will be some cost drop in the beans. In Table 2, 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 Percent M.C. Standard
|Discount of $.12 Per Bushel Per Point of Moisture (2% Per Point of Moisture)||Discount of $.20 Per Bushel Per Point of Moisture (3.3% Per Point of Moisture)|
|Soybean Harvest Moisture, %, Wet Basis||Weight of Water Loss (+) or Gain (-), Lbs/Bu to Convert Soybeans to 13.5% Moisture||$.12 Discount Per Bushel, $||Price Per Bushel, $||Value Per Bushel, $, Adjusted for Moisture||$.20 Discount Per Bushel, $||Price Per Bushel, $||Value Per Bushel, $, Adjusted for Moisture|
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 percent 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 percent 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 percent moisture content.
- A pick-up type reel with pick-up guards on the cutter bar is recommended when beans are lodged and tangled.
Finally, If you would like more reading on this I would direct you to navigate to the Agronomy Journal Publication, D. B. Philbrook and E.S. Oplinger, 1983, Harvest Loss in Soybeans, that address this issue in more detail.