How to accurately assess combine losses

When combining is going well and the crop is feeding like a dream it’s tempting to keep thrusting that hydro leaver forward.

But are those loss monitors really giving a true impression of how much grain you’re throwing over the back? This guide will show you how to accurately assess your losses.

There are six key areas where losses can occur:

1. Pre-harvest losses

Grain on the ground ahead of the combine is usually due to the weather (particularly this season).

Remember to deduct this when assessing overall harvesting losses.

2. Header losses

Additional grain found on the deck directly behind the table is usually lost at the cutter-bar and reel.

Aim to get the crop presented head-on to the auger by adjusting reel speed and position.  

3. Leakage

Grain directly under the harvester body normally seeps its way out of leaky elevator access flaps and

auger sleeves. These can account for large losses which are often mistaken for shoe and walker losses.

4. Sieve losses

If material is allowed to build up excessively on the top sieve, grain will ride out the back of the

combine. Opening the sieves and increasing fan speed will help to minimise this.

To identify sieve losses, scour the ground directly behind the rear axle in a kill-stall.

5. Fan losses

Rarely a major cause of losses, grain can be blown off sieves the back of the sieves.

Check the ground 1.5-2m behind the chaff spreader for fan losses.

6. Walker losses

Unthreshed grain in the straw is usually a result of a slow drum speed or wide concave.

The majority of lost grain is usually found in the straw and can be classified as walker loss.

Measuring total losses requires a little bit of maths but is a fairly straightforward process. Losses

below 1% are generally considered acceptable.

Shake all the grain left in the straw from a 1m section of swath into a suitable container. Then scour the

stubble in that same area for any grain left on the ground – add this to your collection.

Use the following calculation to work out what the combine is leaving behind.

Example of how to calculate combine losses

Six-walker combine with 5.1m (17ft) header working in wheat with an average yield of 8t/ha (3.2t/acre).

Surface P = area being harvested1m multiplied by header width = 5.1 sq m

Surface Q = swath area1m multiplied by swath width = 1.5sq m

Collected losses = 25.5grams (from 5.1sq m of crop)Losses divided by crop area = 25.5/5.1 = 5g/sqm

Losses of 5g/sq m equate to 50kg/ha or 0.6% loss.

Considering a thousand grain weight of 23k/kg, this equates to 586 grains in Surface Q (1.5sq m swath).

Rule of hand

An average human hand covers an area of 0.03sq m. If 18 grains can be found in that area then losses are approximately 0.6% for an 8t/ha (3.2t/acre) crop.