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Harvest Losses, Undercutting Versus Direct Cutting
August 29, 2007

Whats the difference in pinto bean seed loss after harvest, if any, between underground/undercutting and straight cutting techniques?  Other than anecdotal estimates and observations, there hasnt been any data that might help compare losses under the two cutting methods, especially given the increasing interest in direct harvesting.

Terry Gregoire, NDSU Extension area cropping system specialist,
Devils Lake, examined bean fields harvested with both methods last year to get some comparative numbers.  Following harvest, he surveyed 21 dry bean fields chosen randomly in Towner, Ramsey, and Benson, three N.D. counties in the Devils Lake region where dry beans, mostly pintos, have become a stable feature of crop rotations.  Eleven fields were undercut and 10 were direct cut without undercutting roots.

A metal hoop of 1.23 sq. ft. was randomly tossed either behind the combine on the harvested residue pattern or in between the combine residue pattern.  Five sampling locations were selected in both areas for a total of 10 samples.  Beans were counted as shelled or those left in a pod.  Pounds per acre were calculated based on 1,600 seeds/lb for pinto beans and 2,300 seeds/lb for the one field of black beans surveyed.

The area represented by each sample varied among fields and was estimated by measuring the residue distribution width behind the combine.  This distance was used to calculate losses directly behind the combine and the remaining width used to calculate losses between the residue swaths.

Several methods are currently used to underground cut/swath/pick up dry beans, and all these techniques were grouped together in this study.  There are also several methods to cut dry beans above ground, such as swathing, flex head or floating header bars, and all were grouped together as direct cut for the purpose of this survey.

Losses can be lowered under either method
As might be expected, average harvest losses were higher for direct cut methods than undercut methods due to a larger seed and pod loss measured in the area between combine harvest swaths.  Still, Gregoire notes he was a bit surprised that the losses for aboveground methods were as low as they were; that the numbers gap in losses would have been even larger between the two techniques than the averages in this survey.

Losses behind the combine were similar for the two methods, indicating that direct methods have a tendency to shatter more in the cutting and gathering operation that was undercut.  The range of losses was also greater for direct cut methods than undercut methods.

However, the data indicates that losses can be lowered by management under both methods.  The best three undercut fields with the lowest losses (34, 29, 10 lbs/ac) averaged a total harvest loss of just 24 lbs/ac, while the average for the fields with the worst losses (288, 194, 172) was 218 lbs/ac.

There was a sizeable gap in the three best and worst direct cut bean fields as well: direct cut beans averaged 101 lbs/ac for the best three fields (118, 102, 84 lbs/ac) while the worst three averaged 347 lbs/ac (599, 263, 180).

Regardless of the harvest method, it appears that about 200 lbs/ac could be saved by using the best harvest techniques for the situation.  Based on grower experiences and observations, Gregoire says these are factors that can reduce harvest losses:

"        Plant an upright bean architecture.

"        Establish uniform populations and uniform maturities, using desiccants when appropriate to reduce maturity differences.

"        Cut timely when pods are tough at correct maturity and when humidity is higher, such as following dew or rain events, or at night.

"        Use rollers to submerge rocks.

"        Use brush guards and keep sickle blades sharp.

"        Take advantage of improved reel designs for swathers and combine headers to reduce shatter losses.  Grower experiences with direct cut headers suggest that the addition of an air reel and supplemental lifter guards to a flexible cutterbar can reduce loss to 5 to 10% of yield.

Dry Edible Bean Harvest tips

Begin combining when beans reach 18% moisture content, with a combine cylinder speed run only fast enough to do a complete threshing job. It is difficult to give one cylinder speed, as diameters of cylinders and rotors vary from 17 inches up to 30 inches in diameter. It is usually best to set cylinder speed as slow as possible and check to be sure that pods are threshed to allow bean removal without excessive splits and checking.

Maintain as large a concave clearance as possible and still do a good job of threshing. As beans dry down, cylinder or rotor to concave settings should be increased. Check your operators manual for recommended cylinder speed and concave setting. Manufacturers recommendations apply to average or normal conditions and may require variation to meet specific field conditions.

Crowd the combine cylinder to near maximum capacity without overloading. To do this, either use a faster travel speed or put more rows in the windrow. The additional straw going through the threshing mechanism will help cushion the beans and prevent damage.

Set the adjustable chaffer at 5/8 inch and the sieve at 7/16 inch. This should allow the threshed beans and some hulls to fall through the chaffer, and the cleaning sieve will allow only threshed beans to fall through to the grain auger. Use a relatively high fan speed and direct the blast toward the forward one-third of the cleaning shoe. Check your operators manual for specific recommendations.

Check the tailings return periodically.  Note the quantity and composition of the material being returned to the cylinder for rethreshing. Any appreciable quantity of threshed beans in the tailing return indicates that the adjustable chaffer is set too tight. Completely threshed beans returning through the auger for rethreshing will increase the amount of split beans and checked seedcoats.

Monitor the grain tank for dirt and foreign material, and for beans that are split or have checked seedcoats. Excess dirt and chaff generally indicate that the adjustable sieve is adjusted too wide or that the fan blast is inadequate or improperly directed.

Common reasons for excessive checks and splits:

"        The cylinder speed is too high.

"        The cylinder concave clearance is too small.

"        Too many concave bars or grates are being used.

"        Too many completely threshed beans are being returned through the tailings system.

Try to avoid dropping beans from great heights in unloading and handling. Beans check and crack when dropped, particularly on hard surfaces and when dry. Cushion or deflect the fall of beans whenever possible. Keep elevator flight chains snug so that flights do not ride on beans.

How to Measure Harvest Losses

Five simple steps can provide a good harvest loss estimate:

"        Locate three random sites in the field

"        At each site, outline an area that is 1 ft. in the direction of equipment travel and is as wide as the effective width of the implement. For example, if a combine is picking up windrows containing 12 30-inch rows, the width of the measurement area should be 30 feet. Examine the entire width of the implement pass, not just behind the threshing section of the combine where loss can be concentrated.

"        Search the soil surface and through any soil loosened by harvest implements within the outlined area for seeds and unthreshed pods. Count all bean seeds.

"        Divide the number of seeds found by the number of square feet within the outlined area. This will provide the average number of bean seeds lost per square foot. Take an average of the three areas sampled within the field.

"        Use Table 1 to convert average number of seeds lost per square foot to pounds of seed lost per acre for specific seed sizes.

For example, if a sampled area over the full effective width of an implement pass averaged 1 pinto bean seed per square foot, the field loss would be approximately 36 lbs/ac, assuming 1,200 seeds/lb. To extrapolate to 3 seeds/ sq. ft. for the same seed size of 1,200 seeds/lb, one could multiply 3 by 1.0 by 36 lbs/ac = 108 lbs/ac field loss.

Dry bean harvest tips and measuring harvest loss information from the NDSU Dry Bean Production Guide, online at and


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