Training Manual Harvesting
Training Manual Harvesting
Training Manual Harvesting
Harvesting is he process of collecting the mature rice crop from the field. The goal
of good harvesting is to maximize grain yield, and to minimize grain losses and
quality deterioration.
Harvesting
CONTENTS
H1 INTRODUCTION..................................................................................................................... 2
2
2.1
2.2
Harvesting Systems............................................................................................3
2.3
TIMING OF HARVESTING...................................................................................................... 7
3.1
4
HARVESTING OPERATIONS...............................................................................................11
4.1
Cutting............................................................................................................... 11
4.2
Threshing..........................................................................................................12
4.2.1
4.2.2
4.2.3
Manual Threshing.................................................................................................... 12
Machine Threshing.................................................................................................. 13
Principle of Feed-In, Axial-Flow Thresher................................................................14
4.3
Combine Harvesting..........................................................................................16
4.4
Grain Cleaning..................................................................................................18
HARVESTING COSTS.......................................................................................................... 22
7.1
7.2
7.3
7.4
APPENDICES....................................................................................................................... 26
Harvesting
Introduction
Harvesting is the process of collecting the mature rice crop from the field. Harvesting of paddy includes
cutting, stacking, handling, threshing, cleaning and hauling of paddy. The goal of good harvesting methods
is to maximize grain yield, and to minimize grain damage and quality deterioration. Harvesting can be
done manually using sickles and knives, or mechanically with the use of threshers or combine harvesters.
Regardless of the method, a number of guidelines should be followed that will ensure that harvest losses
are kept to a minimum and grain quality is preserved during harvest operations.
Harvesting
2
2.1
Harvesting rice is at the beginning of the rice post-production chain and it consists of five basic operations
and two optional operations:
Harvesting
Cutting
Field drying
Hauling
Threshing
Cleaning
Bagging
Drying
Paddy Storage
Milling
Rice Storage
Marketing
Seeds
Besides these, a variety of other activities can be included in harvesting such as gathering, reaping
(gathering standing grain by cutting), bundling, and various forms of transporting the crop and grain.
2.2
Harvesting Systems
Harvesting systems vary from region to region and include different methods for harvesting, hauling,
threshing and cleaning. The goal of good harvesting is to ensure maximum grain yield through minimizing
Harvesting
grain loss and the prevention of quality deterioration.
A wide variety of tools is used, such as knives, sickles, animals, stationary 1 threshing machines, tractormounted harvesters, and self-propelled2 combine harvesters. In Asia, the most common systems for
paddy harvesting are:
1. Manual harvesting and handling, followed by threshing and cleaning by hand or using
manually operated tools.
This includes use of traditional tools for threshing such as threshing racks, simple treadle
threshers and animals for trampling.
2. Manual harvesting, followed by machine threshing.
Optional:
Winnowing or cleaning
Self-propelled = machine operation has its own power source-is independent of tractor
4
Harvesting
3. Machine harvesting with a reaper followed by machine threshing.
Optional:
Winnowing or cleaning
Cutting and laying the crop on a windrow is done using a reaper, threshing by a thresher and
cleaning either manually or by machine.
4. Combine harvesting.
The combine harvester combines all operations: cutting, handling, threshing and cleaning
The Table below gives an overview of tools used at each stage of the harvesting process in different
harvesting systems:
Harvesting system
1. Manual
Manual harvest &
systems
threshing by beating
Manual harvest &
threshing by pedal
thresher
Manual harvest &
threshing by
trampling
2. Manual harvesting with machine
threshing
Cutting
Cutting with
sickle
Reaper
4. Combine harvest
Hauling
Carrying crop
Threshing
Hand threshing
Cleaning
Winnowing or
grain gleaner
Pedal thresher
Animal trampling
Cutting with
sickle
Collecting and
hauling crop by
hand
Hauling crop by
hand
Feed-in thresher
Feed-in thresher
Winnowing,
thresher cleaner,
or grain cleaner
Winnowing,
thresher cleaner,
or grain cleaner
Combine
Harvesting
2.3
field layout and accessibility: combine harvesters require a certain field layout and access
demand for straw: certain threshers damage the straw making it less marketable.
The table below lists advantages and disadvantages of common harvesting systems:
Method
1. Manual
harvesting and
threshing
2. Manual
harvesting and
threshing/cleani
ng by machine
Description
Cutting, stacking, bundling,
handling and piling by hand
Threshing by beating
Cleaning by winnowing
Cutting and stacking by hand
Threshing by machine
Cleaning by machine or by
hand
3. Reaping and
threshing by
machine
Reaping by machine
Threshing by machine
Cleaning by machine or hand
4. Combine harvesting
Standard
Harvests, threshes and cleans
Combinecrop mechanically
harvester
Cutter-bar cuts crop, while
conveying system feeds crop
into the threshing and cleaning
systems
Threshing drum tip speed 2025 m/s
CombineSame as above except a
harvester with
stripper header is used instead
stripper-header
of a cutterbar
Head-Feed
Combine
Axial Flow
combine
Similar to Conventional
combine harvester, except an
axial flow type thresher is
used.
Advantages
Efficient
Most effective in lodged crop
Winnowing/cleaning necessary
Less weather dependent
More effective in wet season
harvest-wet crop conditions
Higher capacity than manual
Lower labor requirements
Less dependent on field size
Higher capacity than manual
Lower labor requirements
Less dependent on field size
Disadvantages
High labor cost Skill
dependent
Susceptible to grain damage
Higher Cost
More straw left behind in the
field
Less effective in partially
lodged crop
Highest throughput
Less power required for
subsequent threshing and cleaning
operations
Can start threshing earlier in the
day
High mobility
Can operate in small fields
Less power required for
threshing/cleaning Ideal for hardto-thresh varieties
Straw cutting/chopping is easier
Lower
High Throughput
Axial-flow threshing system ideal
for tropical conditions
High Cost
Not suited for small, muddy
Asian fields
Problems in lodged crop
High Cost
Low throughput
Pick-up reel not suited for
indica and other highshattering varieties
Complex machine
Lower cost than conventional
combine harvesters
Harvesting
Timing of Harvesting
Figure 2: Mature rice crop in the field (left) and harvested paddy (right)
Correct timing of harvest is crucial in order to prevent crop loss. Grain losses may occur from rats, birds,
crop lodging, insects, and shattering. Timely harvesting ensures good grain quality and high market value.
Too early harvesting will result in a larger percentage of unfilled or immature grains, which will results in a
lower yield and in higher grain breakage during milling (Figure 3). Harvesting too late will lead to excessive
losses and increased breakage in rice. Timing of harvesting also affects the germination potential of rice
seed.
Figure 3: Grain yield (t/ha), germination (%), head rice (%), and grain moisture content (%) as a function
of time of harvesting (days after heading) in a dry and wet season crop
There are different indicators for the correct harvest time: the amount of ripened grains per panicle; the
average moisture content of the grains; the number of days after sowing; and the number of days after
heading.
Harvesting
Figure 4: Determination of the proper harvesting time by assessing the color of the grains
Ripe grains per panicle: The crop should be cut when 80-85% of the grains are straw (i.e. yellow)
colored.
For harvesting the grain moisture content ideally is between 20-25% w.b. If the crop is too dry, fissures will
form in dry kernels when these are re-wetted and high shattering losses might occur. Fissured grains
break when milled. If the grain is too wet, it is more difficult to remove grain from the panicle and some
damage may occur during machine threshing. Farmers often determine the harvest timing by biting the
grain which allows them to estimate the moisture content. Grains should be firm but not brittle when
squeezed between the teeth.
If the crop has a lot of surface moisture, e.g. from previous rainfall or early in the morning, it is advisable to
wait to cut the crop until the surface moisture dried off. Field drying of the cut crop is not recommended
because the grains dry slower when they are placed on the ground. If field drying cannot be avoided
because a thresher is not available, the grains should be exposed to the sun and not placed inside straw
bundles. During good weather non-threshed crops will normally dry at 1-2% moisture per day when
spread in the field.
Number of days after sowing: Generally the ideal harvest time lies between 130-136 days after sowing
for late, 113-125 for medium, and 110 days for early maturing varieties.
Number of days after heading: In dry season harvest, an optimum time of harvest is 28 to 35 days after
heading which gives best grain yield (see shaded area in graph below), germination, and head rice. In wet
season harvest, optimum time is 32 to 38 days after heading (Figure 3).
Harvesting also needs to be timed in a way that threshing can be done as soon as possible after cutting to
avoid re-wetting and reduce grain breakage. Re-wetting of dry kernels occurs naturally in the field before
and after harvest as moisture transfers from either wet kernels, the soil or from the surrounding air to dry
kernels.
3.1
Of equal importance to the proper time for harvesting is the timely conduction of the individual harvesting
operations, including drying which follows harvest. Any delay between operations leads to rapid
deterioration of grain quality and to increased shattering losses. Immediate threshing reduces the
exposure of crop to insects, birds, rodents, disease, and molds. Crop that is piled over a period of time
generates heat that will serve as an ideal medium for growth of molds, disease and pests. Piling wet rice
crop for longer than one day will lead to grain discoloration, germinated grains, and spoilage (Figure 5).
Harvesting
Figure 5: Piling wet rice crop for a longer period of time results in fermented / discolored grains
In addition to the physical losses in field drying, there is rapid quality deterioration during delays in the
harvesting chain.
Effect of delay of threshing on losses and quality
Ideally, machine threshing should begin immediately after cutting. Often these crops can be threshed in
the field.
Figure 6: Effect of delay of threshing on physical grain quality and on milling yields, using results of the
first day as 100% baseline
Harvesting
If a thresher or laborers for threshing are not immediately available, the harvested crop is either left spread
out in the field for field drying or piled up in stacks or piles for temporary storage. Especially in the piles,
rapid quality deterioration occurs because the grain heats up and adsorbs water from the wet straw. Both
lead to rapid reduction in quality and milling yields (Figure 6).
Effect of delay in drying on quality and losses
A similar decrease in quality and increase in losses can be observed when there is a delay in drying after
the harvest operation (Figure 7). While this module focuses on harvesting, the harvested crop should be
dried immediately after threshing to MC levels that are safe for storage.
Figure 7: Effect of delay of drying on physical grain quality and on milling yields, using results of the first
day as 100% baseline
10
Harvesting
4
4.1
Harvesting Operations
Cutting
Cutting can also be done mechanically by a reaper, although the use of reapers is not wide-spread in Asia.
In some countries, reapers are used that are mounted on the front of a tractor. Most reapers lay the crop
in a windrow, which allows for easy pick up of the harvested crop. A reaper with a cutting-width of 1.5m
can operate at a rate of 2-4 ha per day. For proper operation of reapers, fields need to be leveled and
drained. It is difficult to reap crop that is lodged, lying on the ground.
Harvesting
4.2
Threshing
4.2.1
Manual Threshing
The common method for threshing by hand is separating the grain from the panicle by impact: this is done
by hand beating, treading, or by holding the crop against a rotating drum with spikes or rasp bars. Hand
beating methods are normally used for threshing rice that easily shatters. Manual threshing methods
include:
Foot threshing or trampling: use of bare feet or animals to thresh the crop. To do this
successfully, the crop is spread over a mat or canvass and workers trample with their own feet or
use their animals. A traditional method in some regions is the use of animals to thresh the grain.
Animal treading or trampling is normally carried out at a designated location near the field or in the
village. In some regions, animals have been replaced by tractors. After animal treading, the straw
is separated from the grains and cleaning of the grain is done by winnowing, with or without the
aid of an electric fan.
Beating against a threshing rack: the farmer holds the crop by the sheaves and thrashes it
against a slatted bamboo, wooden platform, or any other hard object such as a steel oil drum.
12
Harvesting
Machine Threshing
Given the high labor requirements of manual threshing, in many countries threshing of paddy is now
mechanized by use of small stationary machine threshers. Depending on farming systems, post-harvest
practices and infrastructure, threshers come in different sizes and range from small portable units without
cleaner (Iloilo, Philippines) to large, truck mounted units (Thailand). Threshing is either done in the field,
near the field or at the nearest road.
Threshers can be classified using different criteria such as feeding type, crop flow inside the machine,
type of threshing elements:
13
Harvesting
Criteria
Feeding type
Type
Hold-on (or head feed)
Feed-in
Crop flow
Description
Only the panicle is fed
into the machine
The hole crop is fed into
the machine
Advantage
Straw remains intact
Low weight
Does not need straw
separators
Good performance with
wet crop
Lowest power
requirement
Thin wire loops comb
grain and thresh through
impact
Wears quicker
Higher throughput
Disadvantage
Lower throughput
Complex machine
Clogging with very wet
or long straw. Higher
power requirement
Higher power
requirement
Axial-flow
Needs straw walker for
separating grains from
straw
Problems in wet crop
Conventional
Threshing
elements
Pegteeth
Rasp bar
Wire loop
Threshers can be classified as either feed-in type or hold-on type machines. Most threshers for paddy
are of feed-in type, where the whole crop is fed through the thresher ensuring high throughput but also
having a high power requirement. Hold-on threshers, in which only panicles are fed into the machine,
generally have a lower capacity than feed-in threshers and are primarily used in areas where rice straw is
bundled and stored for later use. Most threshers for paddy have peg-tooth threshing drums, however
threshing drums fitted with wire-loops are used if power is limited or in hold-on threshers.
Larger stationary threshers are fitted with additional cleaning devices such as an oscillating screen,
centrifugal blower or wind-board, and threshed grain can be handled without further cleaning:
14
Harvesting
The harvested crop is loaded onto the tray and fed into the opening between the cylinder and the concave
at one end of the machine. The pegs on the threshing cylinder hit the material separating the grain from
the straw and, at the same time, accelerating them around the cylinder. The majority of the grain is
threshed during initial impact but further threshing is performed as the material moves axially until the
straw is discharged at the opposite end. Threshed grain, including impurities such as leaves and short
pieces of straw, pass through the openings in the concave and fall onto the oscillating screen where large
impurities are separated.
15
Harvesting
Figure 13: Threshing drum with peg-teeth and concave of an axial-flow thresher
In many regions, machine threshers are owned by individuals who offer custom operations to farmers.
This requires that farmers schedule harvesting dates depending on the availability of the thresher. Many
threshers are mounted on trailers or trucks which enables the operator to quickly move from field to field.
Tips for machine threshing
For best results follow the recommended practices below:
Timing:
Location:
Place the thresher as close as possible to the harvested crop to minimize shattering
loss during hauling.
Placement:
If the thresher has a cleaner make sure that it is leveled for best cleaner
performance. Turn the thresher with the straw and chaff outlets facing the leeward
direction to prevent the wind from blowing chaff at the operator. For very wet crop:
Reduce feed rate and clean the concave regularly from sticky straw and impurities.
Cleaner adjustment: Since crop conditions vary adjust the cleaner for optimum performance for each
situation.
16
Harvesting
Machine adjustments
For minimum grain loss and maximum
quality, always adjust the thresher correctly.
For peg-tooth drums the drum tip speed
should be about 12-16 m/sec. The drum
speed in revolutions per minute depends
on the drum diameter as it can be seen in
Table 1. Higher speeds result in higher
grain damage and de-hulled grains. Lower
speeds increase the amount of nonthreshed grain and result in grain loss.
Lower
speeds
also
decrease
the
throughput of the thresher.
Table 1:
RPM
40 cm
50 cm
400
6.3
8.4
10.42
450
7.07
9.4
11.78
500
7.85
10.5
13.09
550
8.64
11.5
14.4
600
9.42
12.6
15.7
650
10.21
13.6
17.02
700
11
14.7
18.3
750
11.8
15.7
19.64
800
12.6
16.8
21
850
13.4
17.8
22.25
900
14.14
18.85
23.6
17
Harvesting
4.3
Combine Harvesting
In India, China and Thailand the use of combine harvesters for paddy rice is increasing rapidly. Combine
harvesters combine several operations into one: cutting, feeding into threshing mechanism, threshing,
cleaning, and discharge of grain into a bulk wagon or directly into bags. Straw is usually discharged
behind the combine in a windrow.
18
Harvesting
services of contractors. Successful use of combine harvester requires well-drained, leveled fields with a
layout that minimizes the number of turns required in the field.
Grain Cleaning
Grain cleaning after harvest is important as it removes unwanted materials from the grain. Clean grain has
a higher value than grain that is contaminated with straws, chaff, weed seeds, soil, rubbish, and other nongrain materials. Grain cleaning will improve the storability of grain, reduce dockage at time of milling, and
improve milling output and quality. Seed cleaning will reduce damage by disease, and improve yields.
Winnowing: Lighter materials such as unfilled grains, chaff, weed seeds, and straw can be removed from
the grain by using a blower, air fan, or by wind. Winnowing recovers only the heavier grains.
Screening/Sifting: Smaller materials such as weed seeds, soil particles and stones can be removed by
sieving the grain through a smaller sized screen (1.4mm or less sieve opening).
19
Harvesting
Seed cleaning: Malformed, discolored, germinated, broken or moldy grains in seed lots can severely
impact seed quality, viability and vigor. Visually inspect the seed prior to storage and consider removing
these grains from the seed lot.
Seed grading: For commercial seed processing, seed grains should have uniform size and weight. A
variety of commercial equipment can be used to achieve uniformity in seed size and shape. These
include gravity tables, rotary screens, indented cylinders, and length graders.
Seed purity: Maintain seed purity by preventing mixing with other varieties and contamination with other
species.
20
Harvesting
This chapter provides some general health and safety guidelines for harvesting and threshing of rice.
Practicing safety precautions will save lives, maintain health and prevent suffering.
Manual harvesting
When cutting crop with a sickle, always hold the stems with thumb pointing upwards, away from the sickle.
Machine threshing
1. Become familiar with the machine before the first operation. Read the manual that came with the
machine.
2. Never leave the thresher unattended while the engine is running. Keep children away from the
machine. Keep hands and feet away from moving parts.
3. Do not fill the tank while the engine is running.
4. Keep all flammable materials (including dry straw) away from the engine.
5. Do not oil, grease, or adjust the machine during operation. Wait until all moving parts have
stopped before servicing.
6. Do not wear loose fitting clothing that may be picked up by moving parts.
7. While operating, keep all shields and guards in place.
8. Never extend hands or feet into the feed opening of the thresher.
9. Never operate your machine in a closed shed or garage. Exhaust fumes are dangerous to your
health.
10. Do not operate machine with loose peg-teeth, bolts and nuts. Loose peg-teeth may be ejected at
high speeds, causing injury to operators and damage to the thresher.
11. Never remove accumulated straw inside the machine during operation.
12. Keep a first-aid kit at hand.
13. Tie up long hair to prevent entangling.
14. Do not wear neckties or other garments that may be wrapped into moving parts of the machine.
21
Harvesting
Combine harvesting
1. Never attempt to lubricate, clean, adjust, or unplug harvesters when the machine or engine is running.
2. Review the manuals that came with the harvester. Understand the controls before operating.
3. Do not allow anyone to climb onto the machine while it is in motion.
4. Keep children at a safe distance from the machine.
5. Do not operate when very tired. Change operators during the day.
6. Always have a fire-extinguisher at hand on engine-operated equipment.
7. Ensure that the fuel system has no leaks.
8. While refueling, stop the engine and do not smoke.
9. When operating around machinery, wear work clothes that fit snugly.
22
Harvesting
Harvesting Costs
Costs for harvesting paddy can make up a significant portion of the production costs of rice; therefore it is
useful to evaluate harvesting costs. Costs of harvesting rice are often (but not always) estimated in terms
of percent of grain output, as in the following examples
Vietnam: harvesting costs are 8% for manual collection by a crew and stationary thresher
Philippines: harvesting costs are 15% for cutting by sickle and use of trailer mounted thresher
The table below shows an example of costs of the three systems: manual harvesting (including cutting,
threshing, cleaning); manual cutting + machine threshing/cleaning by own labor and machine, and manual
cutting + machine threshing by contracted labor and machine. Please note that the table is an entirely
fictitious example and that actual costs are location and time specific, meaning that they can vary by
region and season. By using a spreadsheet you can estimate harvesting costs for your own situation.
1. LABOR
Labor for cutting and gathering
Labor for threshing
Labor for cleaning + bagging
Labor rate
Total labor requirement
Total labor cost/ha
2. EQUIPMENT
Purchase price thresher
Life of thresher
Capacity thresher
Use per year (100 ha @ 4 ton/ha)
Capital cost/yr (excl interest)
Fuel (3 L/hr; 0.75 $/ltr)
Repair and Maintenance (15% of
capital/yr)
Total equipment cost/ha
3. CONTRACTING
Cost per ha (% of grain)
Value of grain (4 ton/ha)
Total contracting cost/ha
TOTAL
Labor+equip+contr
Estimated threshing and handling
loss (% grain)
Expected grain yield
Costs of lost grain ($/ha)
Total harvesting cost
Total Harvesting costs-equivalent in
grain
Manual cutting,
threshing,
cleaning
Manual cutting,
machine threshing by
contracted labor +
equipment
25 Man-days/ha
15 Man-days/ha
8 Man-days/ha
$ 3 /day/person
48 man-days
$144 /ha
25 Man-days/ha
2 Man-days/ha
1 Man-hours/ha
$3 /day/person
28 man-days
$84/ha
0
0
0
0
0
0
0
0
0
0
0
0
0
$1,000.00
2000 hr
1 ton/hr
400 hr
$200.--/yr
$900/yr
$150.--/yr
0
0
0
0
0
0
0
$12.50/ha
0
0
0
0
0
0
12%
$150 $/ton
$72/ha
$144/ha
5%
$96.50
2%
$72/ha
3%
4 ton/ha
$30/ha
$176/ha
29 %
4 ton/ha
$12/ha
$108.50
18 %
4 ton/ha
$18/ha
$90/ha
15 %
In general, costs of owning equipment are dependent on how often the machine is used. When comparing
23
Harvesting
costs of ownership with contract hiring, there is a break-even point (expressed in terms of tons, hectares
or hours that the machine is used) above which ownership becomes more attractive than contract hiring.
Besides direct costs, there are a number of other factors the farmer or station manager will have to
consider when deciding whether to purchase or to contract hire machinery:
Timeliness of operation
Repair, maintenance
Quality of work
Cost
Skills required for operation
Finance requirements
Ownership
Machine is ready when needed
Own repair and maintenance needed
to reduce downtime
Quality of operation is under control of
farmer
Can be lower if there is sufficient work
on the farm
Operational skills required
Capital outlay + financing needed
Contract hiring
Contractor may not be available
when needed
No expertise needed for repair,
maintenance
Quality of operation in control of
contractor
Costs not dependent of amount of
work
No skills required at the farm
No large capital outlay needed
24
Harvesting
Physical grain Losses during harvesting can be divided into various types, depending on the operation
and the machinery used.
Losses during harvesting/cutting:
a. Shattering loss = premature shedding of mature grains from the panicle caused by birds,
wind, rats, and handling operations. Certain rice varieties shatter more easily than others.
b. Lodging loss = plants with mature grains in the panicles fall on the ground making the grains
difficult to recover.
c.
Standing crop loss = standing plants with mature grains are left standing in the field after
harvesting operations as a result of oversight, carelessness or haste.
For most manual harvesting operations, shattering losses are of main concern. Lodging can be a severe
problem in specific situations such as tall varieties, or high wind.
Threshing loss or unseparated loss = mature grains that remain attached to the panicle in
the straw after completion of the threshing operation. Note that a high threshing efficiency will
lead to low threshing loss, and vice versa.
25
Harvesting
In the field, a number of random quadrants are chosen of 1-2 square meters surface area each. After the
harvesting procedure, all grains that are lying on the ground within the quadrants are collected. Following
collection, the collected grain should be carefully weighed. The loss can be expressed as kg/ha if total
field surface area is known, or as % of total yield, if yield is known. Report all losses on same moisture
content basis, usually 14% MC.
7.2
During the threshing/cleaning operation, wrap the blower exhaust in netting that will collect all chaff,
straws, and grains but does not obstruct the air flow. Collect the grain by cleaning the material, and drying
down to 14% MC. Blower loss can be expressed as kg/ha if total field surface area is known, or as % of
threshed grain, if thresher throughput is known. Report all losses on same moisture content basis, usually
14% MC.
7.3
Place the thresher or cleaner on a large plastic tarp. After the threshing/cleaning operation, gently remove
the machine and collect all grain from the tarp. Scatter loss can be expressed as kg/ha if total field surface
area is known, or as % of threshed/cleaned grain, if thresher/cleaner throughput is known. Report all
losses on same moisture content basis, usually 14% MC.
7.4
Place a large tarp at the straw output of the threshers which will capture all straw. After threshing for a
certain amount of time, examine all the output and manually remove all mature grains from panicles,
straw, and tarp. Thresher loss can be expressed as kg/ha if total field surface area is known, or as % of
threshed grain, if thresher throughput is known. Report all losses on same moisture content basis, usually
14% MC.
26
Harvesting
8 Appendices
Appendix 1: Moisture Content Determination of Grain
Appendix 2: Power Thresher Operation and Maintenance
Appendix 3: Troubleshooting of a Rice Thresher
27
Harvesting
Drying
Storage
Primary losses
Shattering if grain is too dry
Incomplete threshing
Grain damage and cracking/breakage
Spoilage, fungal damage
Discoloration
Fungal, insect & rat damage
Loss of vigor
Loss of vigor
Grain cracking and breakage Over milling
Milling
=
=
=
=
=
=
=
=
Definitions:
Moisture content wet basis
Moisture content dry basis
Initial moisture content, w.b.
Final moisture content, w.b.
Equilibrium moisture content
Initial weight
Final weight
Moisture ratio
From MCdb to MCwb
MC wb
100 MC db
100 MC db
Formulas
[%]
[%]
[%]
[%]
[%]
[g]
[g]
MC wb
MC db
mi m f
mi
mi m f
mf
100 (1)
100 (2)
MC db
(3)
100 MC wb
100 MC wb
(4)
m f mi
Example:
100 MCi
100 MC f
[5]
Moisture content of grain can be measured by using a drying oven, or by using a commercial moisture
meter.
28
Harvesting
Measuring MC with a drying oven:
1. Pre-heat the oven at 130C;
2. Weigh three paddy samples of 10 grams
each and place them inside the oven;
3. Remove the samples after approximately
16 hours, and obtain the final weight of
each sample;
4. Compute the MC for each sample : MC =
(10 - Final weight of dried sample in
grams)*100/(10);
5. Compute the average MC of three
samples.
29
Harvesting
Check all pegs on the threshing cylinder for tightness. Loose pegs will
damage the machine and can be dangerous to the operators.
Examine the peg-teeth for wear. Worn pegs must be rotated 180
degrees or interchanged with those less worn. Badly worn pegs must
be replaced or rebuilt by welding
Make sure there are no loose or missing bolts and set screws.
Tighten or replace as necessary.
Lubricate all bearings with good quality grease. The belt idler and oscillating screen eccentric bearings are
lubricated for life, thus require no lubrication.
Check engine oil and fuel levels. Follow the engine manufacturers recommendations.
Start the engine and allow it to warm up. Feed the thresher with the crop to be threshed for performance
checking. Increase cylinder speed if excessive amounts of unthreshed and unseparated grain are observed with
30
Harvesting
the straw. Optimum threshing and cleaning is obtained with the proper threshing drum speeds (see Harvesting
Reference Manual).
Load the feed tray with harvested crop with the panicle away from
the operator, so it is fed panicle first into the thresher.
Feed the crop at a uniform rate. Adjust the feed rate to match the
condition of the material. Maintain maximum feeding rate without
overloading the engine.
Adjust the angle of the wind-board. For dry paddy, the wind-board
should be set at its maximum inclination. For threshing wet paddy,
the inclination of the wind-board must be reduced. To obtain extraclean paddy, set the wind-board at a low inclination and increase the
air shutter opening. This process will blow more grain over the windboard, but this can be recovered by recycling the separated impurities
through the thresher.
Always use a stick to remove clinging straw from the oscillating
screen to protect hands from possible injury.
Long straw: briefly hold the crop bundles at the feed opening for partial threshing. Longer cut material reduces
machine output and may result in poor threshing and clogging of the machine.
Short straw: Recycling the straw if necessary unthreshed loss is high. Panicle-harvested materials (cutting just
above the flag leaf) may result in high unthreshed losses because the panicles move rapidly through the thresher
without receiving sufficient threshing.
31
Harvesting
Wet or partially decomposed crop: Reduce feeding rate to avoid overloading. Ensures that the cleaning screen
is kept free of clinging straw. Open the cylinder cover periodically to remove straw and chaff accumulation at the
lower concave
30 cm
6.3
7.07
7.85
8.64
9.42
10.21
11
11.8
12.6
13.4
14.14
50 cm
10.42
11.78
13.09
14.4
15.7
17.02
18.3
19.64
21
22.25
23.6
Lubricate cylinder and fan bearings with a good-quality general purpose grease every 25 hours of operation.
Periodically apply a small amount of oil to all hinge points.
Inspect the machine regularly for loose, worn, or damaged peg-teeth, concave bars, cylinder, discharge paddles
and other parts, and tighten, repair, or replace them immediately. Missing bolts or nuts must also be replaced.
Reduce belt tensions by loosening the idler pulley and engine mounting bolts when the machine will not be used
for an extended period to minimize deterioration.
32
Harvesting
Check engine crankcase oil level at least every 4 operating hours and follow the engine manufacturers
recommendations for oil change intervals and oil grade. Be sure the recommended oil level is maintained.
Service the air cleaner, fuel filter, fuel line, carburetor, and spark plug regularly according to engine
manufacturers instructions.
Storage of a thresher
33
Harvesting
Cause
Low cylinder speed
Cylinder drive belt slipping
Worn pegteeth
Defective engine
Hard threshing variety
Over threshing
High engine speed
Low wind-board inclination
Wide blower shutter opening
High blower speed
Overfeeding
Loose or damaged belt
Loose or damaged belt
Loose or damaged pulley
Abnormal metallic
chattering sound
Engine trouble
Machine stalls
Remedy
Increase engine speed. For proper threshing drum
speed see Table 1.
If the pulley is warm immediately after stopping, the
belt is slipping. Adjust belt tension.
Rotate teeth half turn or build-up by welding or
interchange or replace with new pegs.
Service or replace engine.
Use stripper bars.
Remove stripper bars. If problem remains, remove
some peg-teeth from cylinder.
Reduce engine speed.
Increase wind-board angle
Reduce blower shutter opening.
Reduce engine speed.
Open cover and rotate cylinder in reverse by hand
and remove clogged materials. (Warning: Ground
engine spark plug).
Check for damaged belt or idler defect. Change if
necessary.
Check for damaged belt or idler defect. Change if
necessary.
Check drive and driven pulley for defects, loose or
lost screws.
Inspect cylinder and remove any obstructions
found.
Remove clogged material after stopping engine.
Reduce feed rate, especially when threshing wet
paddy.
Remove straw and make sure straw is being thrown
in same direction as prevailing wind.
34