Grain Harvest Losses
Html Editors: Dr.
& Tracy Allrich
Grain Harvest Losses - How Much Can
Harvesting is one of the most important farming operations. Grain loss at
harvesting time is a direct loss of income.
The more grain saved, the greater the returns.
A grain harvest loss study at NDSU indicates
that NOT getting the grain into the machine produces
the major portion of harvest losses. Improvement in operator performance can
have a greater effect on reducing harvest
losses than will new combine designs.
Combine losses can be due to improper
operation and machine adjustment.
Therefore, a thorough knowledge of the combine
and its functions, and
a desire to do
the best possible job, are essentials for good
combine operation. The first step to an efficient combining operation is a
thorough study and
of the operator's manual.
Grain harvest losses result from shattering of the standing
grain, shattering during windrowing,
picking up the window with the combine, and
threshing, separating and cleaning in the
combine. Estimates of acceptable losses for small grains such as wheat, barley
and oats are placed
at 3 percent of total yield. Total yield
is harvested yield
plus harvest losses. It is usually very difficult
to reduce total losses below 1-2 percent so
the operator must decide
on the value of the crop, the cost of combining and
the time available for combining or climate conditions.
Some harvest loss is unavoidable in order
to get a reasonably clean threshing job done
in the time available.
Figure 2 indicates
harvest losses of grain at various moisture contents. The curves indicate
that as grain moisture content decreases,
losses increase. The curve labeled shatter,
reel, cutter bar and pickup loss indicates
that if grain is windrowed
at low moisture contents (below 20 percent), losses can be high. If grain
reaches this stage of maturity, straight combining should
It may be more profitable to harvest damp
grain and dry
it. The extra grain saved will usually more
than pay for the drying.
In an NSDU study, harvest losses were divided
into two categories: shatter-cutter bar losses and
cylinder-separation or machine losses.
Shatter-cutter bar losses include seed
shattering from the standing grain, grain
windrowing or straight combining and
the grain lost in picking the grain up with the combine. Cylinder
and septation losses include
the grain lost by the combine from the straw walkers and
Loss studies show a considerable
amount of grain is left in the field due
to shattering out of the grain heads (Table 1). This can occur at several stages in the
harvest operation. A considerable amount of
grain is lost from the standing grain. A
hailstorm on standing grain can shell heads,
break them off and cause severe lodging
problems. Wind can blow entire heads
down or shell out a number of kernels. As the grain
moisture content decreases, susceptibility to
shatter and birds
becomes greater. Some grain varieties are more shatter resistant than others.
Cutting grain at moisture contents of 20-35 percent will help to avoid
some of the shatter loss.
checks show that combine operators are doing a
good job of setting their combines to thresh
and separate the grain. But more concern should
be devoted to
getting the grain into the machine.
From the test results, 60-80 percent of the total loss in harvesting spring
wheat, durum and
barley is due to shatter and
cutter bar loss. In oats, the shatter and
cutter bar loss about equaled the cylinder
and separation losses.
Farmers usually adjust their machines to
recommendations in the operator's manual for
the particular crop to be harvested. In the
field small adjustments
should be performed
according to field
conditions. Operators often walk alongside
the combine and catch the discharge
from the cleaning shoe with a scoop shovel. This will give some indication
of how much grain is being lost by the threshing and
cleaning parts of the combine, but it will not give any indication
of grain lost before it is picked up by the
pickup speed to conform to ground
travel speed and
to pick grain up gently is important. Excessive pickup speed
strips the grain out of the heads. A desirable
speed is one that appears to gently lift the
windrow as the pickup goes underneath.
The windrow should
be gathered in an up broken, even flow to
prevent shelling of grain before it goes into the machine. A pickup drive
that can be adjusted
on the go is helpful for matching travel speed
to windrow conditions.
Excessive travel speed has been shown to be
one of the chief causes of high losses from windrowing
and picking up windrows.
Travel speeds over 4 to 5 mph tend
to cause excessive loss.
Since it is difficult to save all the
grain, a compromise is made between the speed
of harvest and the amount of grain lost (Figure 3). Excessive losses can occur by delaying
harvest as well as overloading the machine. If
the operator wishes to harvest as quickly as possible, large losses may result due
to overfeeding the machine even if the combine
is properly adjusted.
Losses of over 20 percent on a properly adjusted
machine are possible when combines are greatly overloaded.
Total harvest losses are seldom, if ever, at
In the past, a common practice was to feed
the combine until the engine started to slow down,
then back off slightly on the feed rate. The
best practice is to combine on the basis of an acceptable field
loss rather than the maximum the cylinder or
engine will handle. Most combines have reserve
engine power available beyond the usual
maximum power is needed
for hilly conditions, soft fields
and high moisture grain. The capacity of a
combine is normally determined
by its threshing and separating capacity.
Windrowing grain at the right stage of
growth is extremely important to reduce harvest
losses. Whenever the grain moisture content is between 20 and
35 percent, there will be less total loss from windrowing.
Harvest can usually be completed 3 to 5 days
sooner by windrowing, as grain an weeds
will dry faster and
more uniformly in the windrow. At moisture
contents below 20 percent, the total loss may be less by allowing the standing
grain to dry to safe storage levels and
straight combining grain to dry to safe
storage levels and straight combining unless
weeds or uneven ripening are a problem.
North Dakota State University studies have
shown that most small grains are mature at 35 percent kernel moisture content.
At this stage of growth, wheat kernels are yellow without any trace of green and
can be crushed between the fingers without finding
For best windrower operation, reel speed
should be slightly faster than forward
travel speed and
the centerline of the reel placed 6 to 10
inches ahead of the cutter bar. A fixed
bat reel should be run at a height with the
lowest position of the bat slightly below the lowest heads.
A good job of windrowing
will help produce a good
The ideal type of windrow
is one with the heads on top and
across its entire width. Some criss-crossing
of the straw is desirable to keep the windrow
will up on the stubble. This is especially important when crops are light and
may fall through the stubble. Windrows should
be uniform without bunches and as wide
as the combine cylinder and
feeder if possible. This helps make efficient
use of machine capacity.
Combine operator comfort is an important part of new machine design,
so the operator has been placed inside
an environmentally controlled cab. This
isolates him from the dust and
noise of combine operation but also reduces
his ability to sense machine functions.
To overcome this problem, various types of monitoring equipment are
available such as shaft monitors and grain
loss monitors. Shaft monitors sense the rotation of drive
shafts of machine components such as cylinder,
straw walkers, elevators, fan and straw
chopper. When the speed of any shaft drops
below normal operating speed, a light flashes
or buzzer sounds which indicates
to the operator which area has a problem.
When a combine is operating properly, a large percentage of the grain is
separated at the concave and
the remainder at the walkers. When a combine
less grain is separated at the cylinder
and more must be separated
at the walkers. Overloaded
straw walkers can carry grain out of the combine. An overloaded
or improperly adjusted
sleve cannot separate the grain from the chaff. Grain loss monitors help the
combine operator select the maximum ground
speed that will maintain grain losses at or
below an acceptable level. These units employ an impact detection
system to measure the amount of grain goring over the straw walkers and
sleves. The use of a grain monitor can be compared
to the speedometer in a car. The monitor is
not a substitute for careful machine adjustments
but is a good guide
in selecting travel speed for varying conditions
such as size of windrow and
moisture conditions. A grain loss monitor must
be calibrated to provide
an acceptable grain loss reading. This is done
by finding the loss in bushels per acre and
comparing that loss to a reading on the grain
loss monitor. If the combine is used on different
crops, the monitors are not only useful in limiting maximum speeds
and losses, but can be used
to properly feed the combine for optimum
Measurement of Harvest Losses
Several different methods
of determining harvest losses have been tried.
Counting the seeds in a strip the entire width
of cut is an accurate but time consuming method.
A simple but accurate method to estimate
losses requires the use of a one-foot square frame. Pick a typical area of the
field after the combine has passed.
The steps to follow are:
- Count the kernels left directly
behind the rear of the combine. Count
several separate square foot areas. (A)
- Count the kernels already
in the field due
to shatter and cutter bar. (B)
- Subtract (B) from (A).
the results of step 3 by the ratio: (Width
of windrower Cut (ft)) / (Width
of combine cylinder (ft))
the result of Step 4 by the number of kernels for the particular crop for
one bushel per acre loss (Table 2). This is the approximate machinery loss
in bushels per acre.
Table 2. Number of kernels per square foot equaling one bushel per acre
7. Hard Red Spring Wheat 20 | Oats 10
8. Durum 16 | Sunflowers 3
9. Flax 100 | Corn 2
10. Barley 14 | Soybeans 4
- To find
total loss, add
the count in (B) to the result in Step 4. This gives the total seed
count from shatter, cutter bar and
the total seed count of Step 6 by the
number of kernels for the particular crop for one bushel per acre loss
(Table 20). This will give the approximate total loss in bushels per acre.
- For a percentage loss, divide
the loss in Step 7 (loss in bushels per acre) by the total yield
(harvest yield plus loss) in bushels per
acre for the field.
[(Loss)/(Harvest Yield Plus Loss)] X 100
= % loss
Example: A 20 foot windrower is used
in a wheat field yielding
26 bu/acre, and the combine has a cylinder
4 feet wide.
- A = kernels per square foot
behind the combine = 59 kernels per
- B = Kernels per square foot
to the side of the windrow.
B = 4
- B - A = 59 - 4 = 55 kernels
per square foot.
- Ratio: width
of cut (ft) / width of cylinder
(ft) = 20/4 = 5
Divide 55 bt 5 = 11 kernels per square
11 by 20 (Table 2) = .55 bu/acre = machine loss.
- Total loss = "B"
plus answer in Step 4.
= 4 + 11
15 by 20 (Table 2) = .75 bu/acre = total loss
- % total loss = answer in Step
by harvest yield plus total loss
% loss = [loss / harvest Yield Plus loss]
% loss = [.75 / (26 + .75)] X 100 = 2.8%
to: Dr. Ron Schuler, University of Minnesota, for his work on "Grain
Harvest Losses in North Dakota.")
Minnesota Assocaition of Wheat Growers