Steps to measure harvest losses (and why each is important)

August 10, 2017 - Issue 20

Reducing losses out the back of the combine, which can easily reach up to 5 bushels per acre or more, is a way to add bushels with very limited investment. If you are not currently checking and quantifying these losses, then any attempt to get an idea of what they are is a step in the right direction.

Here are the steps to measure losses:

Step 1: Determine your concentration factor (CF). CF= width of cut / width of sieve. If you are using a web-based app, like the one available at agrimetrixapps.com (add direct link), this step isn’t necessary as the app figures it out for you.

Why calculate CF? The CF takes into account that we are concentrating our losses from a large area into a much smaller windrow.

Concentration factor table.

Step 2: Determine the square footage of the pan you are using to do your checks with (area = length x width). Any size of pan can be utilized; it just needs to be accounted for.

Step 3: Disengage the chopper and spreader and drop straw into a windrow for checking purposes.

Why disengage these tools? Dropping straw is the best way to ensure you have collected the full amount of losses coming out the back of the combine. To check while spreading requires multiple pan throws (increasing human error and time required), puts the “checker” in the line of fire of objects (and dust) that could make there way to the discharge area, and losses are not uniform across the width of spread (particularly behind rotary combines).

The exception to this step is for those combines with stationary-knife choppers directly behind the rotor—this style of chopper doesn’t affect spread and can be left in place. The spreading system still needs to be moved out of the way.

Step 4: Drop a pan, throw a pan or hold a pan. The safest way is to drop a pan from the belly of the combine, held on via an electromagnet or some kind of mechanical/pulley system that can be disengaged from the cab of the combine.

Why use a drop pan? For small-seeded crops like canola, it is impossible to know what your losses are by simply looking on the ground. Much of it can go undetected, camouflaging against the soil and getting lost in the crop residue.

This is what a 5 bu./ac. harvest loss looks like on the ground. Add stubble and residue and this becomes even more difficult to estimate. Drop pans are essential.

Step 5: Separate the chaff and straw, keeping only the seed. Some people will do this using sieves or blowers, but hand separating will also work. Weigh the sample (in grams) or take a volumetric measurement (in millimetres).

Why not just count them? Count methods are recommended for a lot of larger-seeded crops, but counting is not practical for small-seeded crops. For example, with a CF of 6, a 1 bu/ac loss in a 4 ft2 pan is over 2,700 canola seeds.

Step 6: Enter all information (cut width, sieve width, pan square footage, and sample size) into the web based application to find what your losses are, or find it on the charts using your CF. (See the charts below or online.)

Step 7: Redo if settings are changed. Pick up the dropped windrow after engaging the spreading and chopping system again.


These tables (click them to enlarge) represent loss found in a one square foot pan. Divide the sample collected by the square footage of your pan to utilize the charts as per normal. For example, in a four-square-foot collection area, a 1 bu./ac. loss would be 13.36 mL.

Further reading:

How to reduce harvest losses
Read all the Canola Watch articles on this topic
Video: Harvest management and mitigating loss

Canola Watch