Rice Production in Arkansas
Head Rice Yield
Foreign Matter Rice
Rice Stripper Heads
Thresher Speed Separation
Combine Loss Monitors
Safe Operation and Overall Combine Management
Estimating Field Loss
Harvest management preserves rice quality and yield that contribute
directly to profit. Timing field draining and harvest are keys to high
head rice yields. Refer to "Water Management" section to improve drain
timing in preparation for harvest.
Other harvesting factors that affect head rice yield include grain
moisture content, field rewetting of grain, severe threshing impacts and
excessive foreign matter (trash) in rice.
Rice quality may be lower if rice is harvested either at high or low
moisture contents. The ends of wet rice kernels grind off and become
dust as they are processed. Rice may crack if it dries to below 15
percent moisture content. Rapid rewetting, once rice reaches 15 percent
or less moisture content, is a key cause for lowered head rice yields.
Certain varieties, such as LaGrue and Jefferson, may be more susceptible
to head rice reductions than a variety like Cypress if rice drops below
15 percent moisture and is rewetted (rainfall) in the field.
Plant no more rice acreage of one maturity range than you have harvest
capacity. The best way to extend combine capacity is by planting
varieties with different maturities. Planting over a longer period than
you plan to combine rice helps somewhat to spread rice maturity across
more days in the fall.
Head Rice Yield
Head rice yield is the weight percentage of rough rice that remains as
whole rice (three-fourths kernel or greater) after complete milling.
Environmental conditions, such as drought, low sunlight intensity,
disease, inadequate or excessive nitrogen and draining water early in
hot weather, all intensify stress on rice kernels. The tendency of
kernels to break under stress differs somewhat among varieties.
Milling yield is the weight percentage of rough rice that remains as
milled rice; i.e., the sum of head rice and "brokens." The value of
broken fractions varies with market demand, but high milling yield and
low foreign material content may provide $30 to $45 more income per
Trash (blanks, stems, weed seed, etc.) often contains more moisture
than the grain. Milling yield is lowered by the amount of foreign
material in the rough rice sample. Foreign material contributes to
heating on trucks and "fines" block air flow in bins. Consider cleaning
rice that has high foreign material content. Another alternative is
marketing rice with high foreign material content separate from cleaner
rice to maximize income.
Rice grades are U.S. No. 1 through 6 and sample grade, based on quality
discount factors. These include weed seed, red rice, seed mixture,
damaged kernels, chalky kernels, etc.
Rice Stripper Headers
Stripper headers have flexible "fingers" that detach kernels by
flailing through standing rice. Eight rows of fingers are fastened to a
rotating cylinder. Rice panicles are combed through large,
keyhole-shaped openings, leaving the rice plant nearly intact while the
grain flips into the header.
The stripper header cannot harvest soybeans. For soybeans, a flexible
cutterbar is an excellent supplement to a stripper. Growers report that
a rigid cutterbar is not needed unless one cuts grain sorghum.
Skill is important with this new technology. Operating the header too
low gathers unnecessary leaf foliage. A high setting misses low heads,
rapidly increasing gathering loss. Trim both sides of the levee first to
gather low heads of rice. An expert operator develops a "feel" for
setting rotor height to avoid bumping the levee.
The ease of grain detachment and the height of rice heads determine
adjustments. Earlier morning and later evening operation are possible
because little leaf or stalk enters the combine. Combine capacity
increases, especially when stalks are moist or where rice has blown down
Combine settings vary from those recommended with a cutterbar. The
thresher/concave gap is less, making these components condition vital. Worn or
damaged components or skewed concaves should be corrected. To handle more rice,
open sieves a bit wider and increase fan speed to increase airflow. In addition,
check for good airflow distribution across the sieves.
Do not fail to obtain a separation loss monitor; mount the sensor in
the shoe discharge, and keep it calibrated. Overspeeding a
stripper/combine rapidly increases separation losses (Figure 1).
Start with a rotor speed between 400-600 rpm (slower than wheat) and
"fine tune" for conditions. To extend the life of the stripping fingers,
select a rotor speed that is just aggressive enough to remove all the
kernels. Excessive speed adds flag leaves to the grain; inadequate speed
leaves rice in the field. Losses increase as fingers wear. Threshing
rice from the stalk requires excessive rotor speed if worn fingers are
Wherever rice height differs, front hood and header height adjustments
are profitable. The hood should contact rice heads at their midpoint.
Count gathering losses carefully to determine a hood/rotor gap that
maximizes rice recovery. A gap between the hood and the rotor that is
too wide or too narrow increases gathering loss.
Harvester influence on rice yield and milling quality have been
evaluated in an experiment. A Shelbourne Reynolds SR6000 stripper was
compared to rice header, Model 1010 on Case IH 1680 combines. Figure 1
summarizes the field loss of the stripper compared to the rigid header
on a Case I H 1680 combine operating at 3/4 to 1 mph. After selecting
header and combine adjustments, all plots were harvested without fine
tuning. Newbonnet averaged 200 bushels per acre, and Millie averaged 175
bushels per acre green weight. By adjusting the stripper properly, yield
losses of both types of headers are very comparable when operated at the
proper speed. There were no differences in the quality of rice harvested
with a stripper compared to a cutterbar.
Operating thresher speed either too fast or too slow can reduce profit.
Research with a Case I H 1680, equipped with a specialty rotor,
indicated 1000 rpm rotor speed was preferable with Newbonnet; 850 rpm
produced the least loss with Lemont. Lower speed failed to separate some
rice. A proper concave gap (position #3 on a Case I H 1680) was more
important than rotor speed in Lemont; the reverse was true in Newbonnet.
The optimum thresher speed depends on moisture content, volume of
material entering the combine, weeds, etc. Fine tuning forward speed and
header height is especially important to minimize field loss. An
overspeeded thresher may lower milling yield. Harsh impacts with
threshing components are more likely to damage high- or low-moisture
rice. Also, at high-moisture contents, rice is more difficult to thresh.
Threshing components should be inspected for proper installation, wear
The John Deere C T S Combine has a rotary separator that reduces rice
loss that "walks" out in the mat of straw in combines with strawwalkers.
This design increases capacity for harvesting rice because combine speed
was limited by loss over the walkers. The C T S models offer little
advantage over John Deere 9500s and 9600s in other crops.
Proper adjustment and operation of the combine are simplified if rice
is harvested in the recommended 17 to 21 percent moisture range.
Continually adjust the header height to reduce material other than grain
in the combine. Slow forward speed when entering weedy areas or spots of
minor sheath blight infection.
Possible gathering remedies for difficulties with a cutterbar header
are listed in Table 12-5. If you experience a difficulty listed at the
top, refer to entries in that column in numerical order. Solving a
problem may require a combination of entry remedies described along the
Possible remedies for some combine difficulties are listed in Table
12-6. If you have a rotary thresher, a stripper header or a John Deere C
T S, certain of these diagnostics do not apply to those combines. The
diagnostic layout is similar to Table 12-5. If you experience a
difficulty listed at the top, refer to entries in that column in
numerical order. Solving a problem may require a combination of remedy
entries described along the left.
Loss monitors and yield monitors have become valuable management tools;
calibrating them properly maximizes their benefit. Loss monitors require
validating for changes in seed moisture. Sensitivity settings are
relative; but a loss monitor is an excellent diagnostic tool to confirm
that your combine is at its capacity. One indicator of excess forward
speed is separation loss; the signal from a loss monitor helps harvest
more acres without getting too much rice riding out the rear on the rice
straw and chaff "mat."
Combine Loss Monitors
Grain loss monitors may help optimize operating adjustments and forward
speed. Grain loss sensors must be installed properly in the straw and
chaff discharge to intercept rice leaving the combine. The sensitivity
is set so that only grain and not straw segments trigger the indicator.
To check whether a sensor is functional, tap it lightly while someone
watches the monitor needle in the cab. For precision, reset the
indicator for swings in rice moisture content. Calibrate the monitor for
rice by occasionally checking behind the combine to prove that actual
separation loss is proportional to the signal in the cab.
Temporary monitor fluctuations should be overlooked. However, observing
a monitor and the field conditions will quickly highlight conditions
that increase rice separation loss. An alert operator "fine tunes"
thresher speed and forward speed to use his combine capacity while
avoiding excess field loss.
A yield monitor basically provides dry weight yields, based on data
gathered from the moisture sensor and the grain flow sensor. The
processor estimates yield at every point in the field. It is vital to
calibrate for rice to get useful management data. Take several rice
samples to a moisture meter like those used at grain terminals.
Calibrate the yield monitor, compare the readings and confirm the
moisture content of each. Yield monitor information helps to identify
the benefits of good water management, variety selection and pest
management. New uses continue to develop.
Where levees and points are few, yield monitors can be very accurate.
Both the differential global positioning system (D G P S) with the
mapping capability and the nonrecording, instantaneous, non- D G P S
models provide valuable management data. However, the operator must
either harvest a constant width (near full header width) or adjust the
width frequently for partial header widths. To get accurate acreage data
and correct yield per acre data this is essential.
Rice moisture is displayed on the monitor throughout the harvest day.
The processor typically adjusts rice weight to 14 percent m.c. if it is
calibrated properly. If moisture is not properly calibrated or it is
biased by residue, the processor converts the data to incorrect yields.
If a light rain settles on the rice heads, it biases the moisture sensor
in the clean grain delivery. The processor then adjusts the dry weight
down to 14 percent rice and consequently, records lowered yields
(without real reason). If the display moisture content rises more
rapidly than justified, it is wise to check the metal sensor for
residue. Plant residue may stick on the metal sensor without an apparent
cause. When sampling in the grain tank, always check that the metal
sensor is smooth and shiny (no residue). Until the sensor is thoroughly
clean, erroneous readings persist, even for years! Moisture errors are
one of the most common errors that exceed 2 percent.
Operation and Overall Combine Management
Always make only one adjustment at a time. Then check combine
performance under normal operation. Count losses in the field, evaluate
the bin sample and monitor the tailings throughout the harvest day.
If the cutterbar or feed elevator entry plugs, stop the combine engine
before reaching into the header to remove the obstruction. Never attempt
to manually remove obstructions or perform maintenance with the thresher
turning. Replace all shields and covers after repairing or adjusting the
combine components. Do not engage power before all guards and shields
are in place. Dont fail to give ladders and overhead work your full
attention. Falls from combines are the most common combine accidents.
They may cause lifetime paralysis and have caused death to a number of
Never work under a combine header without securely blocking the lift
cylinder. Men have been crushed under a header making adjustments when
the hydraulic system failed. Others have been pinned when someone else
bumped the header lift control.
Use auxiliary flashing lights when operating a combine on a public
road. Combines are large and motorists may not be alert to equipment
moving less than 25 mph. Make every effort to move on roads during
well-lit daylight hours.
Estimating Field Loss
Field loss has often ranged from 4 to 6 bushels per acre. Combines typically
experience a few percent.
One good evaluation of combine operation is to count field loss. Also,
check the amount of trash and hulled kernels in the bin and the
proportion of trash in the tailings. Table 12-7 is based on sampling a 5
square foot area entirely across the header. Use these sample dimensions
for counting loss and divide the number of kernels lying within the
sample area by 5 to obtain total field loss per square foot.
The last step is converting this loss number to bushels per acre using
Table 12-8. Use the number at the head of the column that is nearest the
loss value per square foot and read the entry in the right column.
- For good head rice yields, avoid extremely early- or late-season
seeding. Apply nitrogen at recommended rates and distribute it
- The recommended harvest range to avoid quality or yield reductions is 17
to 21 percent moisture. Plan combine capacity to be able to complete harvest
by the time rice reaches 16 percent.
- One percentage point reduction in head rice costs up to 2 1/2 cents per
bushel. One percentage point reduction in broken rice costs about 1 3/4 cents
- Use the lowest practical thresher speed for varieties that tend to break
more easily, especially for rice moisture levels below 16 percent. Use more
spike bars or narrow the concave spacing to obtain more aggressive threshing
with a conventional cylinder. .
- Rice lost from the back of the combine typically results from overloading
the separator. To remedy:
- Raise the header as high as feasible.
- Check threshing adjustments.
- Slow down. Even though listed last, this is a sure remedy.