Calculating harvesting losses

Serious grain losses at harvest reduce the profitability of crops. Grain can be lost at a number of places during harvest. The loss should be assessed at each place so that the corrective action can be taken.

When adjusting a harvester to reduce losses, make only one adjustment as a time, checking the losses after each change.

Grain can be lost:

  • pre-harvest, due to natural shedding
  • at the front, due to front type (comb, open front or modified) or set-up
  • from the threshing system of the machine, due to drum, concave and sieve settings.

All these losses may be reduced by resetting the machine and changing the harvesting technique.

Assessing losses

Follow these steps to check all the loss areas without starting and stopping the machine several times.

  1. Harvest a typical area.
  2. Allow the machine to clear itself of material.
  3. Back the harvester about 10 metres and stop the machine.
  4. Sample grain losses in each of the three areas (pre-harvest, front and machine) with at least 10 samples in each area. Average the 10 samples in each area.

Sampling with a quadrat

Use a sampling quadrat with an area of 0.1m2 (see Figure 1). Count the number of seeds lying within each quadrat.

Quadrats can be made from any material, for example, round bar or flat mild steel. For measuring pre-harvest losses, use a three-sided quadrat.

Three and four sided quadrats
Figure 1 Four and three-sided quadrats with areas of 0.1m2

The number of seeds in a quadrat of this size which correspond to a loss of 100 kilograms per hectare for different crops can vary by plus or minus 20%. Table 1 is a useful guide.

Table 1 Average seed number per 0.1m2 for 100kg/ha loss
Crop type Average seed number
Wheat 27
Barley 23
Oats 29
Lupins 7
Chickpeas (desi) 6.5
Lentils, red 33
Lentils, green 28
Yellow lupins 7.5
Field peas 5
Faba beans 2.5
Chickpeas (kabuli) 2
Canola * 267

*For canola, an easier measure is 60 seeds in the area of a 2L ice cream container (0.022m2).

Sampling a canola crop

The easiest method of assessing the losses in canola is to use 2L ice cream containers. Put eight containers in the uncut crop in front of the harvester, four either side of where the harvester will go, to measure the front losses and four in the middle of the machine, to measure the front plus machine losses. Then harvest the crop over the top of where the containers are and count the number of seeds in each container. Remember the concentrating factor when you calculate machine losses (see Figure 1).

Pre-harvest loss

Sample Area A (Figure 2) for pre-harvest loss, that is, losses before harvest due to natural shedding. Take at least ten samples from an area 2-3 metres into the standing crop, using the three-sided quadrat. Count the seeds in each quadrat, including any seeds in pods or heads on the ground and find the average number of seeds per quadrat, then use the following method to calculate pre-harvest loss.

Pre-harvest loss (kg/ha) = [Average number of seeds per quadrat x 100] divided by [the corresponding crop type average seed number from Table 1].

Worked example for an average of five lupin seeds per quadrat in Area A:

Pre-harvest loss = [5 x 100] ÷ 7 = 71kg/ha

Front loss

Sample Area B (Figure 2) to estimate front loss, plus pre-harvest losses. Take at least 10 samples across the full width of the machine to within 0.5m of the edge of the cut.

Front loss (kg/ha) = [(Average seeds per quadrat x 100) minus pre-harvest losses] divided by [the corresponding crop type average seed number from Table 1]

Worked example for an average of 10 lupin seeds per quadrat in Area B:

Front loss = [(10 x 100) - 71] ÷ 7 = 72kg/ha

Machine loss

Sample Area C (Figure 2) to estimate machine loss, plus front loss, plus pre-harvest loss.

Sampling places for estimating pre-harvest, front and machine losses.
Figure 2 Sampling places for estimating pre-harvest (A), front (B), and machine losses (C)

The machine losses may be concentrated in a stream, that is, the width of the sieves if there is no chaff spreader, so the losses must be related to the width of the cut.

Take at least 10 samples across the full width of the sieves. First, carefully take the straw off the header trail, then count the seeds, including the seeds in the unthreshed heads.

Machine loss (kg/ha) = [Average number of seeds per quadrat x 100] divided by [the corresponding crop type average seed number from Table 1] minus [front loss - preharvest loss] multiplied by [sieve width divided by width of cut]

Worked example, for an average of 22 lupin seeds per quadrat, with sieves 1.5 metres wide, 9 metre wide cut and using 0.1m2 quadrat:

Machine loss = [( 22 x 100) ÷ 7] – [71 – 72] x [1.5 ÷ 9] = 28kg/ha

If the harvester has a chaff and straw spreader, it is more difficult to measure the machine loss. Measure the average number of seeds in equally spaced quadrats across the full machine width after the spreader has passed over and subtract the front loss and the pre-harvest loss.

Worked example, if an average of 12 seeds per quadrat is measured across the harvester width, the machine loss is:

Machine loss = [( 12 x 100) ÷ 7] – [71 – 72]  = 28kg/ha

Total harvest loss

Total harvest loss = pre-harvest + front loss + machine loss.

Based on the above example;

Total harvest loss = 71 + 72 + 28 = 171kg/ha

Acceptable losses

Generally, harvest losses range from 0-5% of the yield in cereal crops and from 5-30% in lupins. What is acceptable varies with the operator; some are not concerned with losses of 5% in wheat and 30% in lupins but others do not want any losses.

If a contractor is being used, an agreement should be reached on acceptable losses before the crop is harvested and losses should be checked at the start of harvest. For example, if a lupin harvesting contractor does not have any header improvements, the losses may be expected to be at the high end of the loss range.

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Page last updated: Tuesday, 5 September 2017 - 11:59am

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