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Published October 28, 2013, 11:26 AM

Harvesting for maximum soybean yields

Yield loss can be as high as 15 percent.

By: SDSU Extension Service, SDSU Extension Service

BROOKINGS, S.D. — Soybean harvest started nearly a month ago, but many fields remain to be harvested. Mark Rosenberg, South Dakota State University Extension agronomy and weeds field specialist reminds growers that combines can be operated to reduce harvest loss without affecting the harvesting rate.

“Many adjustments will be a compromise between limiting harvest loss to acceptable levels and maintaining grain quality,” Rosenberg says.

Numerous studies have been conducted in the past 40 years on soybean combine losses, which show that yield loss can be as high as 15 percent.

“Although modern platform headers for soybean have reduced harvest loss to a minimum, do not expect it to be zero. Combines can be operated to reduce harvest loss without affecting the harvesting rate,” he says.

Rosenberg encourages soybean growers to shoot for harvest loss under one bushel per acre in good field conditions. The key to minimum loss, he says, is to adjust the combine for crop conditions.

Causes of harvest loss

Harvest loss results from a combination of gathering loss, pre-harvest loss and machine loss.

Rosenberg explains that gathering loss is when harvested soybeans don’t get inside the combine, and accounts for around 80 percent of the total harvest loss. The amount of gathering loss is impacted by the combine’s ground speed, cutter bar conditions and the location and speed of the pickup reel. To reduce gathering loss, he encourages growers to take care when setting the combine.

“Soybean threshing needs to be just aggressive enough to remove beans from pods,” Rosenberg says.

If beans are small, such as in a drought year, growers may need to check air flow.

“Air flow may need to be reduced in the cleaning shoe and the openings in chaffer and sieve screens reduced to maintain air speed, yet allow beans to fall through,” he says.

He adds that the threshing unit, cylinder-concave or rotor-grate may also need to be adjusted for a smaller clearance. In the cleaning area, the cleaning sieve and the airflow may require adjustment.

If plant population is small and more pods will be close to the ground, Rosenberg says it is essential to keep the cutter bar low.

“The front drum of the feeder should be low enough so that the chain just clears the floor of the feeder house,” he says. “If plants are shorter, smaller clearances may be needed between the reel, cutter bar, auger and the feed conveyor chain, to make sure stalks are feeding through the platform.”

Rosenberg reminds growers to pay attention to the height of the crop stubble left in the field. Crop stubble protects the soil by limiting exposure to wind and water erosion and by trapping snow in the fall, winter and early spring.

“An even distribution of crop residue while harvesting is critical,” he says.

He explains that large headers make the job tougher because they tend to concentrate material behind the machine. Grain platforms up to 30 feet wide collect residue into a 5-foot swath.

“Concentrated crop residues can insulate the soil’s surface from the sun, reduce seed-to-soil contact, and make it tougher to plant in the spring,” he says. “Getting that material spread back out can be difficult. Doing a good job of spreading chaff and stalks can minimize the amount of tillage needed to plant the crop next year. Set the combine so that straw and chaff spreaders or choppers operate properly and the combine distributes residue evenly.”

To better distribute residue, he encourages growers to consider redirecting or increasing airflow from the combine’s chopper to spread light particles farther.

Estimate harvest loss

Rosenberg encourages growers to sample areas of their field to determine what average harvest loss is and determine if there are equipment modifications they can implement to reduce this loss.

“Make loss determinations at several locations and calculate an average. Sample a 10-square feet area of the field. If 40 soybeans are lost in this area, it will add up to one bushel per acre. If losses are greater, machine adjustments need to be made,” he says.

To keep harvest loss to a minimum:

n Keep a level seedbed.

n Keep the cutter bar as close to the ground as possible.

n Don’t drive too fast. Most combines today with platform headers are able to operate without problems at 3 to 4miles per hour. If you use a row-crop header you can go a little bit faster. But if you use a rigid platform, you can’t go as fast as with a platform header or a row-crop header.

n Use a reel speed about 10 to 25 percent faster than ground speed (up to 50 percent faster if the crop is lodged).

n Keep the reel axle 6 to 12 inches ahead of the cutter bar and as low as possible. Reel bats should leave beans just as they are cut and the reel depth should be just enough to control the beans.

n Complete the harvest as quickly as possible after beans reach 13 percent moisture content. Damage increases at lower moisture content (10 percent) as well as at excessive moisture (more than 14 percent).