As much as 20 per cent of your crop could be travelling through and then out the back of the combine. Here’s how to measure how much you’re losing

Have you ever driven down the road and noticed combines working across a field so quickly they would outrun a good jogger? It’s no wonder deer seem to favour these fields later in the fall — harvesting too quickly can blow a surprising amount of grain out the back of a combine.

If you feel the need for speed when operating a combine, you’re going to pay a price for it, according to research done by North Dakota State University (NDSU). Their work reveals overloaded combine losses can reach 20 per cent of a crop’s total yield.

How much money would that cost a farmer? Assuming a 30-bushel-per-acre canola crop worth $8 per bushel, a 20 per cent combining loss amounts to $48 per acre.

“There is a myth that started when rotaries came out: people said you’re just not filling it up enough, push it harder,” says Les Hill, manager of business development and technical services at PAMI (Prairie Agricultural Machinery Institute). “But in all the years we tested combines, it was a rarity that you ever saw losses go down the faster you went. When they (combines) start to lose r. p. m. and work hard, that loss curve starts going up. The reality is speed determines loss; the more material you stuff in there the more loss you’re going to get.” And that applies to both conventional and rotary combines.


It’s impossible to avoid threshing losses completely; getting a clean sample in the hopper and minimizing grain losses amounts to a trade-off. But by carefully adjusting a combine and timing field operations correctly, total harvesting losses can drop to no more than three per cent in cereals, according to NDSU. Here are some tips on how to shoot for that target.

1. First, get the grain into the combine. The NDSU study found as moisture content decreases, losses from cutting a crop increase. If cereal grains are swathed at less than 20 per cent moisture, losses from shattering can be unacceptably high. If moisture content is below that, leaving crops standing until they have dried to safe storage levels and straight combining them is NDSU’s recommendation.

2. If you are going to swath cereals, do it when they are in the 20 to 35 per cent moisture range. Most cereal kernels at or below 35 per cent are mature, according to NDSU’s findings.

3. Setting the reel height so the bottom of each fixed bat is just below the lowest grain heads is optimum. The centre of the reel should be six to 10 inches (15 to 25 cm) ahead of the cutter bar. It should travel just slightly faster than the machine’s ground speed.

Adjusting the combine pickup speed is the next step. When it’s properly set, it should appear to gently lift the windrow as the pickup moves underneath it. That should keep a smooth, even flow of grain into the feeder house. Once again, travel speed is critical. High ground speeds increase losses, even with a pickup. The NDSU notes those speeds should not exceed four to five m. p. h. (6.5 to eight km/h).


When it comes to the combine, Hill says producers should be prepared to spend most of a day getting the initial adjustments correct. “It’s especially important with a new (or new-to-you) machine,” he says.

Going through that process will help familiarize producers with a combine’s performance characteristics, and it will help save time in the long run. “Once you have it established that you know where to look and what to look for, then you can do it (make adjustments) fairly quickly,” says Hill. “Until you know that, you’re just guessing.”

If the combine has a chopper on it, be prepared to take it off, at least for the initial setup. It’s

Weighing method—all crops determining pounds per acre


Loss collected behind combine per. sq. ft. in grams per. sq. ft.









6.2 7.3 8.3


0.5 0.8 1.3 2.6 3.9 5.2 6.5












9.4 10.9 12.5


0.7 1.1 1.8 3.6 5.5 7.3 9.1












12.5 14.6 16.7


0.9 1.4 2.3 4.7 7.0 9.4 11.7












15.6 18.2 20.8


10 15 25 50 75 100 125 150 175 200

Three steps to calculating harvest losses

Collecting the kernels found in a one-square-foot area on the ground behind a combine allows a farmer to determine how many bushels or pounds per acre are being lost. Once you have the kernels collected (in a catch pan), it’s time to make some calculations. Here’s a step-by-step guide to help get you through the process.

1. Determine the “concentration factor.” That is the ratio of cutter bar (or swather) width to the width of the discharge at the back of the combine. For example, a combine equipped with a 30-foot header and a five-foot discharge width has a concentration factor of six (30/5 = 6).

2. Weigh the kernels found in the catch pan. Make sure to remove any chaff, leaving only a clean sample. Use a small digital scale to get an accurate reading.

3. Use the above chart to determine the pounds-per-acre loss. Read the sample weight under the column with the correct concentration factor to get pounds per acre.

impossible to accurately measure grain losses through a chopper.

And Hill says you need to pinpoint where kernels found behind a combine came from. There are several potential sources. “People will look on the ground and just assume they are coming out of the separator or grain shoe,” he says. “It could have been on the ground under the swath because it (the crop) was overripe when it was windrowed, or it could be a leak somewhere on the combine.

“What you’re trying to do is determine where the losses are coming out from side to side and front to back,” he says. “I use a one-square-foot catch pan, which is a dish-pan, on the end of an adjustable handle. I walk along and I can sample at different spots to determine where that grain is coming from.”

The handle allows the pan to be precisely placed under the combine, which is easier than trying to throw it under a moving machine. This method also allows for a person to walk alongside a combine and hold the pan in place or precisely drop it and let the combine drive over it, depending what part of the combine is being checked. And a person walking can keep pace with the combine taking several samples in a relatively short distance, rather than running to catch up or waiting for it to come back on another pass.

Hill says he made his sampling pan from an ordinary Rubbermaid container and broom handle purchased from a hardware store, a very Grainews solution.


After finding the source of the losses, the next step is to measure how much you’re losing to see if it’s an acceptable amount. Counting the number of kernels dropped in a one-square-foot area

— Source: Combine Seed Loss Guide, Canola Council of Canada and PAMI

behind a combine is a way for producers to equate the loss to a bushels-per-acre number. “The one-by-one (square foot) is a standard reference,” says Hill.

But, he adds, taking only a single, one-square-foot sample can be deceiving, partly because combines tend to pulse material through. That can lead to high concentrations of kernels on the ground in some spots, and very few in others.

To compensate, he recommends farmers using small, one-foot-square catch pans take several samples and average the count or use larger pans that cover up to four square feet.

There are a few ways to make sense of the findings. The captured kernels can be weighed and related to bushels per acre by weight; that provides the most accurate loss picture (See sidebar on how to calculate loss rates). A second option is to pour the kernels into a graduated tube with millilitre measurements on it and relate the results to bushels by volume. Or just count the kernels and approximate that number to bushels per acre (roughly 20 kernels per square foot for wheat and 14 for barley).


Now that most combines are equipped with loss monitors, some farmers make the mistake of using monitor readings to adjust combine settings. But a loss monitor doesn’t provide a complete picture. “You’re only sampling some portion of the loss,” says Hill. “It doesn’t sample every kernel that goes out. It can be fooled.”

For example, Hill says if an operator makes an incorrect adjustment, such as increasing fan speed, kernels may be thrown over the sensor, causing the monitor to show a reduction when, in fact, the loss rate has increased. “They’re great if you relate them to the actual (loss),” says Hill. The only way to do that is to manually check losses and compare them to monitor readings.

But when you put the combine to work in the field, how fast is too fast? There is a simple way to find out. Keep increasing the combine’s working speed and measuring losses until they become unacceptably high. “Just keep pushing its speed and manually checking the loss. Then you back off and say I don’t want to go any faster than this. You dial in your loss monitor to indicate that (limit) for you,” explains Hill.

Scott Garvey is machinery editor for Grainews.

About the author


Scott Garvey

Scott Garvey is a freelance writer and video producer. He is also the former machinery editor at Grainews.



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