Plant Establishment

Table Of Contents
TABLE OF CONTENTS ....................................................................................... 1

INTRODUCTION TO PLANT ESTABLISHMENT ................................................ 2

SEED QUALITY ................................................................................................... 2

ENVIRONMENTAL CONDITIONS THAT AFFECT SEED ESTABLISHMENT ... 4

DIRECT SEEDING ............................................................................................... 6

TRANSPLANTING ............................................................................................... 7

PLANTING MACHINES ....................................................................................... 9

SEEDING RATES AND PLANT POPULATIONS .............................................. 11

GERMINATION TEST ........................................................................................ 12

PLANT ESTABLISHMENT TEST ...................................................................... 13

CALIBRATING SEEDING RATE - HAND BROADCASTING............................ 14

CALIBRATING A DIRECT SEEDER.................................................................. 15

PRE-GERMINATING SEED ............................................................................... 16

FIELD EXERCISE 1. PLANT ESTABLISHMENT STUDIES.............................. 16

FIELD EXERCISE 2. PLANTING EQUIPMENT ................................................. 17

1
Introduction to plant establishment
Rate of plant establishment is affected by three factors: quality of seed, environment in which
seed is placed, and manner in which seed is metered and delivered. Number of plants
established and seedling vigor will affect competitiveness of the crop against weeds, and
ultimately determine final yield potential.

Seed quality
Seed quality is the summation of all attributes that contribute to seed performance. Seeds of high
quality are true to variety, and have high percentages for vigor and germination. The main criteria
for describing seed quality include purity, percentage of seeds that germinate, and vigor with
which they germinate.

Purity refers to genetic or varietal purity. It is also a measure of the degree to which seed is free
of seeds from weeds (other crops or species) and inert material (stones, dirt, or twigs). Purity is
expressed on a percentage basis by weight.

2
 With impurities Without impurities

Germination percentage expresses the proportion of the total number of seeds that are alive. It is
determined through controlled tests and actual counts of the number of seeds that germinate.

Seed vigor is an important factor that may explain the causes of poor seedling establishment.
Seeds low in vigor generally produce weak seedlings that are susceptible to environmental
stresses. Seeds high in vigor generally provide for early and uniform stands that give seedlings a
competitive advantage against environmental stresses.

The seedling

Seed size and plumpness and/or fullness indicate that the seed has potential to produce vigorous
seedlings under favorable conditions.

Seed health. High quality seeds should be free from seed borne disease, weed seeds, and other
extraneous matter. They should also be free from various types of mechanical injury that reduce
germination and seedling vigor.

3
 Quality seeds

Environmental conditions that affect seed

establishment
To start growing, a seedling
• absorbs moisture from its surrounding environment
• establishes a root system in a moist layer of soil
• has its shoots and leaves break out above the soil surface.

Several environmental conditions affect a seedling’s capacity to do this:

• contact between the seed and soil water
• depth at which seed is placed
• number of pests present.

Seed soil contact

To begin the germination process, the seed absorbs a certain amount of moisture from its
surroundings. In a dry seed bed, absorption occurs after distribution through the seed being in
contact with moist soil or being submerged in water. For seeds to make good contact with the
soil, soil peds (clods) need to be similar in size to the seed and actually make physical contact
with the seed. Seed soaking or seed priming prior to planting expedites the absorption process
and is often used to increase the rate of plant establishment.

4
 Soil size

Seed placement

Rice seeds must be placed close to the soil surface. When dry seeding into heavier clay soils,
place seeds within 10 to 15 mm of the surface. If seeds are placed at depths greater than this,
surface sealing will restrict the number of shoots that emerge and increase the time to
emergence. When wet seeding, seeds should not sink below the puddled surface. Where
possible the water is allowed to partially clear before seeding. This may require waiting for up to
48 hours after puddling.

Soil insects and disease

Plant establishment can be slowed down by the following soil borne insects: nematodes, crickets
and wireworms. Some of these problems are alleviated by cultural controls: crop rotation, trap
crops, and bare fallowing. Seed dressing protects the seed from insects that directly attack the
seed. For stem and root protection, it is necessary to use the appropriate pesticide through
surface application or soil fumigation.

5
 Pesticide Application

Planting Techniques

The most suitable planting technique depends on locality, soil type, and crop ecosystem. Crops
can be direct seeded or transplanted. Similarly transplanted crops can be established manually or
by machine. Direct seeded crops tend to mature faster than transplanted crops but have more
competition from weeds.

Direct Seeded Crop Transplanted Crop

Direct seeding
Direct seeded crops can be established using dry seed or pre-germinated seed and seedlings.
They are broadcast by hand or planted by machine.

Dry seeding

In rainfed and deepwater ecosystems, dry seed is manually broadcast onto the soil surface and
then incorporated either by ploughing or by harrowing while the soil is still dry. Care is taken not
to incorporate the seed too deeply into clay soils or where surface sealing is a problem.

In some deepwater rice areas, the seed is not incorporated after broadcasting. Germination
occurs following rain or floods. To achieve an acceptable level of establishment, the farmer allows
for the following factors: seed quality, soil tilth, amount of seed incorporation, and expected
availability of water.

The target number of plants to be established ranges from 100 to 150 plants per m2. To meet this
target, seeding rates vary between 80 and 250 kg per ha. Some plant rearrangement
(transplanting) is normally undertaken within the field after establishment, to even up plant
stands. Broadcasting is a very efficient way of reducing labor requirements; normally one or two
people can plant one hectare per day.

Pre-germinated seed and seedlings

In irrigated areas, seed is normally pre-germinated prior to broadcasting. Seedlings can be

broadcast onto recently drained, well-puddled seedbeds or into pre-standing water in the fields. If

6
water in the fields is muddy following the last working, the field is allowed to dry for a time period
of at least 24 hrs (preferably 48 hrs) before broadcasting commences. If water is drained from the
fields after broadcasting, it is re-introduced 10 to 15 days after establishment. In some irrigation
areas, seedlings are broadcast post-germination with seedlings 100 to 300 mm in length.

Direct Seeding

Transplanting
Transplanting of rice seedlings into puddled fields is widely practiced in Asia, primarily as a
means of weed control. Transplanting requires less seed but much more labor, and the crop
takes longer to mature due to transplanting shock.

Seedling nurseries use 15 to 20 percent of the total farming area. In preparing the nursery
seedbed, make sure the surface is level, free of weeds, and well drained. Some form of nitrogen
and phosphate fertilizer is applied to the nursery. Seeds are pre-germinated and can be
broadcast into either a flooded or wet soil surface in the nursery. Seeding rates vary from 500 to
800 kg per nursery hectare depending on locality, soil type, and seed quality

While the majority of rice fields in Asia are manually transplanted, China, Japan, and South Korea
also use mechanical transplanters.

Prior to transplanting, seedlings are grown for varying lengths of time in the nursery. Local
varieties are transplanted 40 to 80 days after establishment; improved varieties are transplanted
within 20 days after establishment. Machine transplanted seedlings are transplanted 15 days
after establishment

Seedlings are normally hand transplanted 20 cm apart, but this distance may be increased or
decreased depending on soil fertility and water supply. The range is normally 15 to 30 cm. Most
mechanical transplanters place seedlings in rows 30 cm apart with in-row spacing determined by
forward speed.

7
 Hand transplanted Machine transplanted

In some sandy soils, transplanting is undertaken within hours of final harrowing else the soil
becomes too hard to manually implant the seedling. In areas where there has been insufficient
rain, transplanting may also be undertaken in non-flooded soil by using a stick to create the hole
to implant the seedling. In some localities, transplanting is delayed for two to three days after the
final working because the soil is too weak to support the seedling. Pulling and transplanting of
seedlings is very labor intensive. Depending on soil type, one hectare of rice requires 30 to 40
person days to establish.

Seedlings for Hand Transplanting Hand Transplanting

Seedlings for Machine Transplanter Mechanical Transplanter

8
Planting machines
Many different types of planters are used to direct seed rice.

Dry seeder

In Australia and the United States, seed is often placed by a seeder into both dry and moist soil
and then irrigated. In Asia, mechanical planting of dry seed is seldom practised. In other
countries, rice seed is planted into well-prepared seedbeds using traditional seed drills.

Seed Drill

Seed drills have many different types of furrow openers, which are designed for different soil
types and crop residues (Table 1). A smooth, level seedbed is necessary to ensure that seeds
are not planted at depths greater than 10 to 15 mm. Covering harrows are drawn behind the
combine. Sowing is at the correct depth is when five to ten percent of the seed is visible on the
surface after sowing.

A good plant stand has 35 to 40 plants established per meter of drill row after permanent water is
applied to the field. A benefit of drill seeding is that fertilizer can be applied at the same time as
the seed. Manual weeding is much easier in machine-drilled crops than in broadcast crops.

Furrow opener Remarks

Rotating
Double disk Suitable for high residue conditions.
Single disk Better penetration in hard soils but wider
variation in seed placement.

Fixed-type
Chisel Narrow furrow. Good for deep sowing and in
friable soils.
Hoe Good for stony, harder soil conditions and for
deep placement.
Inverted ‘T’ Use for reduced till in free flowing soils.
Can leave open furrow in wet soils.

Runner For shallow depths in loamy non-smearing soils.

9
Shoe For placing seed and fertilizer in separate
bands.
Shovel Deep placement causing much soil disturbance.
Table 1. Suitability of furrow openers in different working conditions

Drum seeder

The manually operated drum seeder is used for some wet seeding in eastern Asia. The drum
seeder operates best on a seedbed that is very level, smooth and wet. The drum seeder is very
heavy to pull and can leave gaps and multiple seedlings in the planted row. Uneven seeding
occurs: many seeds are dropped when the operator stops, and then no seeds are dropped until
the seeder has moved forward for a small distance. Uneven seeding leads to a very uneven plant
stand and follow up transplanting may be required.

Drum Seeder

Transplanter

In Asia, a number of different transplanters are successfully used to establish rice. Machines are
manufactured in China, Japan, Korea and Taiwan with varying levels of complexity. Machines
range in size from a two-row, walk-behind models to eight-row, ride-on models.

For seedling production, mechanized transplanting requires techniques that are different from
hand transplanting. Seedlings are often grown on a thin layer of soil in 30 cm x 60 cm trays. In
some instances, seedlings are grown on larger areas and then cut into rectangular strips ( mats
of seedlings) that fit into the planting trays of the transplanter. Seedlings can be planted out 10 to

10
15 days after establishment.

Seeds sown on trays Seedlings

Land must be well prepared for machine transplanting. The soil needs to be level and have
sufficient bearing strength to carry the machine and support the planted seedlings. Fields may
need to be drained one or two days longer than they are for hand transplanting.

Seeding rates and plant populations

Seeding rate and desired plant population depend on several factors: the rice ecosystem,
planting technique, planting depth, seed quality and seed variety.

Total number of panicles required per unit area can vary, depending on soil type and water
regime. For most situations, tillers and panicles are thought of as similar although not all tillers
produce panicles. For wet season crops, 300 to 400 panicles per m2 are desired; in the dry
season density increases to 500 to 600 panicles per m2. In more fertile soils and for irrigated and
dry season crops, plant populations should be increased.

Rice Panicles

Each plant develops three to seven tillers. The number of tillers will vary according to nutrient

11
status, variety and planting rate (higher seeding rates normally give fewer tillers). Transplanted
crops generally produce more tillers than direct seeded crops, and dry season crops often
produce more tillers than wet season crops.

Plant establishment rates for broadcast crops are less than for transplanted crops. When planted
in nurseries, 60 percent of the seeds will establish. This will reduce to 50 percent when broadcast
directly into the fields. Planting rate ranges from 80 to 250 kg ha-1 for broadcast crops and 500 to
800 kg per nursery hectare for transplanted crops.

Number of seedlings transplanted per hill depends on three factors: country, quality of seed, and
price of seed. Hybrid seed, which is more costly, is often transplanted as one seedling per hill
while some local varieties are planted with 5 to 6 seedlings in each hill. Most countries plant two
to three seedlings per hill.

One plant per hill 5 to 6 plants per hill

Depth of planting affects both crop establishment and lodging potential. Broadcast crops tend to
lodge more because with the seed germinating at the surface, the crown of the plant is at or
above ground level. Care must be taken with seed placement as rice seeds have difficulty
establishing if placed too deep in the soil. The following table shows that seeding and water depth
greatly influence percent emergence.

Seeding Water Germ'n (%) Seeding Water Germ'n (%) Seeding Water Germ'n (%)
depth (mm) depth (mm) depth (mm) depth (mm) depth (mm) depth (mm)
0 0 95 13 0 80 25 0 40
0 13 90 13 13 60 25 13 35
0 25 92 13 25 60 25 25 31
0 38 90 13 38 60 25 38 20

Germination test
A germination test is often the only test a farmer can conduct on his seed before planting.
Monitoring the time taken to germinate will also give an indication of vigor. This procedure is very
easy, inexpensive and portable.

Sampling

To obtain a random sample for testing it is always best to take samples from different parts of the
bag or container. If the grain to be tested is from a seed lot that contains more than one bag,
samples must be taken from several bags. A good rule of thumb for determining how many bags
to sample is to take samples from a number of bags that represents the square root of the lot
size. For example if the lot contains nine bags, then sample at least three bags. If the lot contains
100 bags, then sample at least 10 bags.

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Equipment

To conduct this test you will need the following:

• Waterproof tray. A flat-sided water bottle, cut in half lengthwise, makes a good tray.
• Water absorbent material. Tissues or cotton wool are ideal.
• One hundred seeds.
• Water supply.

Procedure
1. Place water absorbent material inside waterproof tray.
2. Take random sample from each seed lot and mix in a container.
3. Take at least three seed samples from the mixed grain.
4. Count out 100 seeds from each sample and place on absorbent paper inside the tray.
5. Carefully saturate absorbent material.
6. Each day check that absorbent materials remain moist and record number of germinated
seeds. Do this for 10 days.
7. Compute germination test for five days and ten days
8. Rate of germination is an indicator of vigor. Rapid seed germination increases the chance
that seed will establish in the field.

Calculating germination rate

Germination rate is the average number of seeds that germinate over the five-day and 10-day
time period.

Germination (%) = Number seeds germinated x 100

Number seeds on tray

Example
If 86 seeds germinated in a tray of 100 seeds

Germination (%) = 86 x 100 = 86 %

100

Plant establishment test

The number of plants established in the field relative to number sown is the final analysis of
success of the planting operation. When determining desired plant populations, farmers
inadvertently make allowances for seed quality, soil conditions, seed application techniques, and
pests. The procedure to measure establishment rate is very easy, inexpensive and requires little
equipment.

Sampling

Sites within the field must be selected at random and be representative of the whole field. This
can be done by

• following a predetermined pattern using transects across the field and sampling at a
preset distance along each transect, or
• randomly throwing a quadrant or marker into different parts of the field.

A transect that is N-shaped or W-shaped and starts at one corner of the field is best. Number of

13
samples taken in each field depends on field size and variability in plant stand. A minimum of ten
sites should be sampled in each field; number of sites sampled should be increased for larger
fields, especially if large variations in plant numbers are recorded. Avoid selecting sites where
plant numbers are known to be either high or low.

Equipment

To conduct this test you will need the following:

• A quadrant. Minimum size 50 cm x 50 cm, but 1 m x 1 m is preferred.
• Recording material. Pencil is preferred to ink pen.

Procedure

1. Determine sampling techniques. Either transect or throwing quadrant or marker.

2. Place quadrant at selected site. When using distance measurements it is best to place
the quadrant corner in line with some part of your foot. The same positioning should be
used each time.
3. Count and record the number of seedlings. Be careful not to count tillers or other grass
species.
4. Add up the number of plants recorded for all the quadrants counted in each field and
divide by the total quadrant area.

Calculate establishment rate

Establishment rate is the average number of seeds that are established in the field after planting.

Establishment rate = Number plants

Area (m2)

Example
786 seeds established per 2.5 m2

Establishment rate = 786 = 314 per m2

2.5

This can be expressed as an establishment percentage if the 1000 seed weight and the planting
rate in kg per ha are known. Depending on variety, each kilogram of seed will contain between 40
to 50,000 seeds. Therefore each 100 seedlings established per square meter represents 2.0 to
2.5 kg of seed per ha.

In the above example, 314 seedlings per m2 represent 7 kg per ha of seed.

Calibrating seeding rate - Hand broadcasting

Establishment of the correct plant population which is evenly distributed in the field or nursery, is
critical to minimize cost of planting and to maximize crop yields. To attain these goals, farmers
must convert a planting rate in kg per ha to an equivalent weight of seed for a given area and
then apply that seed evenly across the field.

Procedure

To help broadcast the seed evenly, markers should be placed at either end of the field to guide
the applicator. Maximum width of throw or distance between markers should be no greater than
five meters.

To determine weight of seed required per sector,

14
 • Measure width and length of area to be sown in each pass.
• Calculate area as a decimal of one hectare.
• Multiply desired planting rate per hectare by area

Example

Therefore,

Dimensions = 100 m long, 5 m wide

Planting rate = 80 kg per ha

Therefore,
Area = 10000/100/5 ha
= 0.2 ha

Seed required = planting rate (kg per ha) x area (ha)

= 80 x 0.2
= 16 kg per section (500 m2)

Calibrating a direct seeder

Establishment of the correct plant population is critical to minimize cost of planting and to
maximize crop yields. To attain these goals, farmers must calibrate a planting machine. Farmers
can use many techniques. The basic requirement is the weight of seed collected for a given area.

Procedure

1. Determine required planting rate and set machine settings on that rate.
2. Measure width of machine (W).
3. Determine distance traveled for 50 revolutions of metering drive wheel of the seeder. This
is best done on the surface to be planted by driving the planter across the seedbed for 50
revolutions of metering drive wheel and then measuring distance covered (D).
4. Place seed in seed bin.
5. Either in static position with drive wheel above the ground turn drive wheel 50 turns and
collect seed from at least five outlets, or drive planter across seedbed for 50 revs of
meter wheel and collect seed from at least five outlets (T)
6. Weigh seed in grams (A).
7. Calculate seeding rate.

Seeding rate (S) (kg per ha) = A x T x10,000

NxDxW

Where
S = Seeding rate
A = seed from five tubes
T = total no of tubes on machine
N = no of collection tubes
D = distance in 50 revs meter drive wheel
W = width machine

Example
1500 gm seed was collected from five seed tubes

15
 20 seed tubes on machine
50 revs of meter wheel measured 25 meters in distance
Machine is four meters wide.

Therefore,

Seeding rate (S) (kg per ha) = 1500 x 5 x 10 = 15 kg per ha

50 x 25 x 4

Pre-germinating seed
Pre-germinating the seed increases rate and percentage of seedlings established. Pre-
germinating, or soaking of seeds, reduces the time required for seeds to uptake sufficient
moisture to initiate the germination process. Seeds are normally pre-germinated when directly
sown into wet puddled seedbeds or standing water.

Procedure
1. Submerge the bag of seed in water for 24 hours or until small shoots appear at end of
seed. In some cases this may take 36 hours.
2. Dry the seed in bag for 24 hours.
3. When drying seed make sure it is kept in the shade and air is allowed to circulate around
bags. If bag temperatures exceed 42 degrees Celsius, then some seed will be damaged
or sterilized.
4. Broadcast the seed before roots exceed 5 mm in length.
5. When calculating the planting rate, make allowance for expansion in seed volume.
Depending on variety, the seed may increase by 10 to 30 percent of its original weight.

Field Exercise 1. Plant establishment studies

There are many different ways to establish rice crops. The method selected will depend on soil
type, type of land preparation, water availability, time of year and local customs. This exercise is
designed to study rice plant establishment from seed germination potential to plant establishment
in the field. It does not involve transplanting although transplanted crops are established in
nurseries using any one of these techniques.

Necessary techniques include the following: germination test, plant establishment test, seed
cleaning, and calibration.

Planting systems that will be compared are as follows:

• Dry seeding (broadcast) and then irrigating
• Dry seeding (broadcast) into water
• Primed seed (overnight soaking)
• Pre-germinated seed onto wet surface (nursery establishment)
• Pre-germinated seed into standing water
• Machine-seeded and irrigated (demonstrated in exercise for whole group)

Requirements to complete this exercise are as follows:

1. Grade the seeds.
2. Undertake germination test.
3. Determine seed required to plant plots at 100 kg per ha equivalent.
4. Pre-germinate the required amount of seed.
5. Measure plots and determine amount of seed to be broadcast into each plot.

16
 6. Broadcast seed into plots and irrigate where necessary.
7. Monitor rate of establishment.

Outcomes
1. Calculate number of seeds in one kg of seed.
2. Calculate percent of light seeds in the bag sample.
3. Calculate change in weight by pre-germinating seed for 24 hrs.
4. Plot rate of establishment for each technique for four days, six days, and eight days.
5. Determine most appropriate technique or system for your environment.

Field Exercise 2. Planting equipment

1. Observe different planters and systems. Note the seed metering system, delivery tubes,
furrow openers, and furrow closers.
2. Discuss advantages and disadvantages of using different planting equipment. Note
suitability for different seeds, application of fertilizer, soil conditions, and weeding ability.

17
Index
1
10-day ........................................................................................................................................... 12
2
24
bag............................................................................................................................................. 16
water.......................................................................................................................................... 16
5
50
reduce ....................................................................................................................................... 11
traveled ..................................................................................................................................... 15
500
increases................................................................................................................................... 11
A
Affect............................................................................................................................................... 4
seedling’s.................................................................................................................................... 4
Affect seed establishment ............................................................................................................ 4
And/or ............................................................................................................................................. 2
Asia ............................................................................................................................................. 7, 9
Australia ......................................................................................................................................... 9
B
Bag ................................................................................................................................................ 16
24 ............................................................................................................................................... 16
C
Calibrating .................................................................................................................................... 15
direct seeder............................................................................................................................. 15
Celsius .......................................................................................................................................... 16
China........................................................................................................................................... 7, 9
Closers.......................................................................................................................................... 17
Competitiveness ............................................................................................................................ 2
D
D 15
Deepwater....................................................................................................................................... 6
Direct............................................................................................................................................... 6
Direct Seeded Crop Transplanted Crop......................................... 4
Direct seeder ................................................................................................................................ 15
Calibrating ................................................................................................................................ 15
Direct Seeding................................................................................................................................ 6
Drum Seeder .................................................................................................................................. 9
E
Environmental conditions ............................................................................................................ 4
F
Field Exercise......................................................................................................................... 16, 17

18
 G
Germination test .......................................................................................................................... 12
Germ'n .......................................................................................................................................... 11
H
Ha-1 ............................................................................................................................................... 11
Hand.............................................................................................................................................. 14
Hand Transplanting Hand Transplanting.............................................. 7
Hrs............................................................................................................................................. 6, 16
I
Increases ...................................................................................................................................... 11
500 ............................................................................................................................................. 11
Introduction.................................................................................................................................... 2
plant establishment ................................................................................................................... 2
Inverted ‘T’...................................................................................................................................... 9
J
Japan .......................................................................................................................................... 7, 9
K
Korea............................................................................................................................................... 9
M
M 13, 14
M2.................................................................................................................................. 6, 11, 13, 14
Machine ...................................................................................................................................... 7, 9
Planting ....................................................................................................................................... 9
Machine Transplanter Mechanical Transplanter.......................................... 7
Machine-drilled .............................................................................................................................. 9
N
N 15
N-shaped ...................................................................................................................................... 13
P
Peds ................................................................................................................................................ 4
Pesticide Application .................................................................................................................... 4
Plant establishment....................................................................................................................... 2
Introduction ................................................................................................................................ 2
Plant establishment test ............................................................................................................. 13
Plant populations......................................................................................................................... 11
Planting....................................................................................................................................... 4, 9
machines..................................................................................................................................... 9
Techniques ................................................................................................................................. 4
Post-germination ........................................................................................................................... 6
Pre-germinating ........................................................................................................................... 16
seed ........................................................................................................................................... 16
R
Rainfed............................................................................................................................................ 6
Rates ....................................................................................................................................... 11, 14
Seeding ..................................................................................................................................... 11

19
Reduce.......................................................................................................................................... 11
50 ............................................................................................................................................... 11
Rice Panicles................................................................................................................................ 11
S
S 15
Seed Drill ........................................................................................................................................ 9
Seed quality.................................................................................................................................... 2
Seeding................................................................................................................................... 11, 16
Pre-germinating ....................................................................................................................... 16
rates........................................................................................................................................... 11
Seedling’s....................................................................................................................................... 4
affect............................................................................................................................................ 4
Seedlings........................................................................................................................................ 9
South Korea ................................................................................................................................... 7
T
T 15
T x10
000 ............................................................................................................................................. 15
Taiwan............................................................................................................................................. 9
Techniques..................................................................................................................................... 4
Planting ....................................................................................................................................... 4
Traveled ........................................................................................................................................ 15
50 ............................................................................................................................................... 15
U
United States.................................................................................................................................. 9
W
W 15
Water............................................................................................................................................. 16
24 ............................................................................................................................................... 16
Wireworms ..................................................................................................................................... 4
W-shaped...................................................................................................................................... 13

20