United States

Department of

Agriculture

Forest Service

Southern Forest

Experiment Station

New Orleans,

Louisiana

Research Paper

so-177

November, 1981

Measurement and

Management of Tree

Seed Moisture

F. T Bonner
SUMMARY

There are two kinds of tests for routine measurements of tree seed moisture,

(1) accurate measurement (such as official International Seed Testing

Association tests) and (2) rapid estimates. For small seeds (more than 30,00O/kg)

such as pine, fir, spruce, sweetgum, birch, or cherry, the suggested accurate test

consists of weighing 4- to 5-g samples, oven-drying them at 103 * 2°C for 17 +- 1

hr, weighing again, and calculating the difference as percentage of moisture.

For non-destructive, rapid estimates with small seeds, use an electric meter for

measuring 80- to 200-g samples (depending on the make of meter). Large seeds

(less than 30,00O/kg) such as oaks, walnut, beech, or hickories must first be

ground, cut, or broken and sample weights should be equivalent to the weight of

five seeds. Then accurate measurement can be made by the same oven-drying

techniques as for small seeds and rapid estimates can be made by weighing,

microwave oven-drying, and weighing again.
Measurement and Management of Tree Seed Moisture

I? ‘I! Bonner

INTRODUCTION

All those who handle tree seeds (nurserymen, seed

orchard managers, commercial seed dealers, or others)

should be vitally interested in the moisture conditions

of the seed stocks that they manage. The levels of seed

moisture can influence or indicate (1) seed maturity,

(2) longevity in storage, or (3) the amount of pretreatment needed. Seed moisture is the most important

factor affecting the retention of viability in storage.

For “orthodox” seeds (seeds that can be stored at low

moisture content (such as pines or sweetgum) experience has provided some general guidelines for potential damage in storage (table 1).

These guidelines do not apply to seeds that must be

stored at high moisture levels to retain viability, commonly called “recalcitrant” seeds. The most common

recalcitrant seeds in the United States are oaks.

Seed moisture should be measured (1) when seeds

are cleaned and ready for storage, (2) 2 or 3 mo after

the start of storage, (3) every 1 or 2 (at most > yr of

storage, and (4) before and after seed lots are shipped.

The three general types of seed moisture measurement

are (1) oven-drying/gravimetric measurement, (2)

rapid measurements with dielectric meters or similar

devices, and (3) laboratory procedures, such as toluene

distillation or Karl Fisher titration (which are used in

research only and will not be discussed further).

SAMPLING

As in germination testing, the proper drawing of a

sample for moisture testing is very important. Accurate measure of a sample’s moisture is of little help if

the sample is not representative of the seedlot.

Sampling Equipment

Free-flowing seeds (such as pine or sweetgum) in

containers should be sampled with seed triers which

are long enough to reach all areas of the containers.

The best triers are those with a hollow, slotted brass

tube on the inside of a slotted outer shell or sleeve (fig.

1). Several sizes are available, and one must choose

a trier large enough in diameter to admit the seeds

freely.

Large seeds (such as oak or hickory) and seeds that

are not free-flowing should be sampled by thrusting

the hand into the seeds and removing small portions.

The hand should be inserted flat with fingers extended

together, and closed as it is withdrawn. It is difficult to

sample deeper than 40 cm with this method, and containers may have to be partially emptied to facilitate

sampling.

Table l.-Potential damage at various moisture contents in stored

seeds

Seed moisture content

Below 5%

5-6%

lo-18%

18% and above

30% and above

Source: Harrington 1973.

Potential case of damage

lipid autoxidation

very little-ideal for storage

active fungal grown

heat from respiration

nondormant seeds germinate

Number of Samples

Ideally, the sample should be made up of equal portions taken from evenly distributed volumes of the lot.

The number of samples should be proportional to the

size of the container; if part of a lot is in 40 liter

containers and part in 80 liter containers, twice as

many portions should be taken from the 80 liter containers as from the 40 liter ones.

The Association of Official Seed Analysts has suggested these sampling guidelines (Association of Official Seed Analysts, 1975).

(1) For lots of one to six containers, sample each

container and take a total of at least five cores or

handfuls.

(2) For lots of more than six containers, sample five

containers plus at least 10 percent of the number

of containers in the lot.

For seeds that have not been mixed recently (such as

stored seed stocks), subsamples should be taken from

the top, center, and bottom thirds ofthe containers and

combined. As containers are handled, empty seeds and

wings have a tendency to work to the top, and they

usually exhibit different moisture characteristics from

filled, dewinged seeds.

F. T Bonner is Supervisory Plant Physiologist, Southern Forest Experiment Station, Forest Service-USDA, Starkville, Mississippi.

1
Figure L-Sampling seed with a slotted trier.

Care of Sample

Samples taken from seed in cold storage should be

drawn and packaged under storage conditions. Packaged samples can be opened when they reach room

temperature (usually around 2 hr). When cold seeds

come into contact with warm, moist air, moisture will

condense on the seeds, and seed moisture content will

increase. The humidity is usually low in airconditioned offices and laboratories and seed exposure

for short periods is less critical there, unless the sample moisture content is high.

MEASURING SEED MOISTURE

Oven-drying Techniques

Oven-drying techniques are now the standard techniques for oficial determinations of seed moisture in

regulatory and other seed laboratories. Seeds are

heated at prescribed temperatures for prescribed

times, and all weight loss is considered to be moisture.

Weighing samples before and after drying provides the

data for calculation of moisture content.

Pretreatment of Samples.-Small seeds (such as

pines, sweetgum, or green ash) can be dried intact.

Larger seeds (such as acorns, or nuts) must be broken

into smaller pieces, so that all internal moisture can be

driven off in the oven. A good rule of thumb is that any

seeds that average over 10 mm in diameter or length

should be broken.

Official international rules (International Seed

Testing Association 1976) require the grinding of large

seeds so that 50 percent of the ground material can

pass a sieve with a mesh size of 4.0 mm. But with seeds

of high oil content (such as walnut, hickories, or beech)

or seeds with high moisture content (such as oaks),

grinding is difficult. A satisfactory alternative to

grinding is to rapidly cut or break the seeds into small

pieces. Acorns can be cut with hand pruning shears

(fig. 2). Nuts of h’ic kory and walnut can be put in cloth

bags (to prevent the pieces from scattering) and broken

with hammers.

Grinding, breaking, or cutting should always be

done on a larger sample from which the actual

measurement sample (commonly called the “working

sample”) can be drawn. For example, a sample of 5 to

10 seeds should be rapidly mixed prior to drawing the

working sample, which should equal the weight of 5

seeds. Working samples for small, intact seeds should

be 4-5 g.

Spoons or spatulas should be used to handle moisture samples whether intact seeds or cut pieces; handling seeds with fingers can sometimes leave a residue

of skin moisture on the seed surface.

Drying Equipment.-Seeds should be dried in containers of noncorrosive metal or glass that have a flat

bottom, rounded sides at the base, and a snug-fitting

cover. The sample should be spread evenly on the bottom of the container to allow good air circulation (fig.

3). There should be no more than 0.3 g of seeds per cm’.

Either gravity-convection or mechanical-convection

ovens may be used, but preferably the latter. Good

insulation and good thermostatic controls are also

needed. Most laboratory ovens distributed by scientific

supply houses in the United States are sufficient.

Drying Schedules-Seeds of all tree species can be

dried at 103 ? 2°C for 17 + 1 hr. Accurate moisture determinations can be made on some species by drying at

130°C for 4 hr (Bonner 19721, but this has no advantage

over the lower temperature unless time is critical. The

lower-temperature schedule is normally preferred, because the drying period of 17 f 1 hr fits an overnight

schedule very well; samples put into the oven at the

close of a work day will be ready to cool and weigh the

following morning. Timing the 17-hr period should not

be started until the oven temperature reaches 103°C

with the containers inside.

One potential problem is overcrowding the oven

2
Figure 2.-Acorns cut into quarters with hand pruning shears.

with containers to the point that air movement (and

thus moisture removal) is impeded. Space approximately equal to the diameter of the containers should

be left open between containers during drying (fig. 4).

Cooling.- For accurate weighing, the containers

and their seed material should be cooled in desiccators

for 30-45 min before dry weights are recorded. With

rapid-weigh electronic balances in air-conditioned,

low-humidity laboratories, this cooling step can be

skipped, if necessary, since it takes about 30 s for hot

(103°C) samples to absorb a measurable amount of

moisture from the air.

Weighing and Calculations.-All weights should be

measured to three decimal places. Modern electronic

balances are ideal for rapid sample weighing (fig. 5).

Moisture contents should always be expressed as a

percentage of the wet weight of the sample. Gravimetric determinations in oven-drying procedures are

calculated to one decimal place:

percent moisture = wet weight - dry weightx 100

wet weight

Tolerance.-Duplicate determinations should be

made for each seed unit. The arithmetic mean of the

duplicate measurements is taken as the moisture content. In official tests (International Seed Testing Association 19761, if the difference between these measure-

!lhble 2.--Suggested tolerances for variability in seed moisture tests

Sample condition Tolerance (%)

Small seed@, moisture < 12% 0.3

Large seedsb, moisture < 12% 0.4

Small seeds, moisture > 12% 0.5

Large seeds, moisture > 12% 0.8

Large seeds, moisture > 25% 2.5

“For example: pines, firs, sweetgum.

bFor example: hickories.

ments exceeds 0.2 percent both must be repeated. But

for many tree seeds, this tolerance limit is not reasonable; experience has shown that as seed size increases

and as seed moisture content increases, natural

variability ofthe test material will make it increasingly difficult to meet the tolerance limit of 0.2 percent. In

large seeds (such as hickory or walnut) or in highmoisture seeds (such as oaks) the 0.2 percent tolerance

may be met only 10 percent of the time. Only with,

small seeds, such as many pine species or sweetgum,

with moisture contents below 10 percent is the 0.2

percent tolerance reasonable. More realistic tolerantes for moisture tests are given in table 2.

A step-by-step procedure for oven-drying technique

is given in Appendix I.

3
Electric Moisture Meters

In many instances very rapid measurements of seed

moisture content are valuable. Electric moisture

meters that work on the principle of electrical resistance or capacitance offer such a possibility for nondestructive testing. Meters available in the U. S. were

designed for cereal grains, and they will work only on

small tree seeds that flow easily and settle uniformly

into the narrow measurement chambers (fig. 6). Dewinged pine seeds, sweetgum, sycamore, and depulped

black cherry are some of the seeds suited to measurement in electric meters. Acorns are too large, and

winged seeds, such as ash or maple, will not settle

uniformly.

Most meters will determine moisture contents within 1.0 percent or less of the “true” moisture content

determined by oven-drying. This is not accurate

enough to be accepted for official testing, but it is

certainly good enough for decisions on seed handling.

One drawback is that most meters will not measure

moisture above 15-20 percent. Decisions on such matters as suitability of a lot for storage could still be

made, but in the case of some moist seed lots, the

inability to measure moisture of this level could be

damaging. Seed quantity could also be a problem for

researchers or tree improvement workers who deal

with small lots. Most electric meters require 90-200 g

of seeds for a test.

Operation.-Electric meters are built to indicate the

total amount of moisture in the measurement chamber, so conversion of meter readings to percentages of

moisture requires that a constant sample weight be

Figure 3.-Metal can for drying samples by the oven method.

used every time. Samples should be transferred to

rapid-weigh balances by spoon or spatula (not with

hands), and quickly dumped into the measurement

chamber. As in the oven-drying technique, the seeds

should be at room temperature.

As soon as the sample is in the measurement chamber, the meter reading should be recorded. This reading is then related to seed moisture content by means

of a calibration chart for each species and each make of

meter. A step-by-step procedure is outlined in Appendix II.

Calibration Charts.-Calibration charts for one

meter currently in wide use for tree seeds in the U.S.

are found in Appendices III and IV. Charts for other

species can be easily prepared from paired measurements of electric meters and oven-drying.

At least 10 lots of the seeds should be used. These lots

should weigh at least 0.5kg each, and they should have

different moisture contents. If moisture levels of some

samples must be changed by adding moisture, then

they should be allowed to equilibrate for 2 wk before

measurements are made.

Meter readings are taken on samples of each lot, and

subsamples (5-10 g) are drawn from these samples for

moisture determination by oven-drying. Sample

weight will depend on the make of meter and type of

seed, but it must be the same for all samples. The

measurement chambers should be full if possible, and

always more than half full.

Meter readings can then be plotted against ovendrying data for construction of a curve. More accurate

determinations can be made by calculating regression

equations.

Microwave Drying

Large seeds (such as acorns or hickory nuts) will not

fit the measurement chambers of electric meters. It is

possible, however, to make rapid moisture content

estimates fo.r these seeds by drying them in home microwave ovens. The seeds must be cut or broken (just as

in oven-drying techniques), weighed, dried, and reweighed (fig. 7). Moisture content is calculated just as

in oven-drying.

One moisture determination can be made in about 5

or 6 min with a microwave oven. Limited experience

with this method has shown large error limits for

acorns (6-7 percent) but smaller errors for shagbark

hickory (1 percent) and green and white ash (2 percent)

(Banner and Turner 19801. These error limits reflect

the variability of the sample material more than

inherent errors in the procedure. Without alternatives

for the large tree seeds, this method has promise. A

step-by-step procedure for the microwave method is

found in Appendix V and typical drying times for some

species with a particular microwave oven are given in

Appendix VI.

4
Figure 4.-To allow optimum air movement within the oven, leave spaces between containers equal to their diameter.

Figure 5.-Modern electronic balances are ideal for rapid sample weighing.

5
Figure 6.-One type of electric seed moisture meter than can be used

on some tree seeds.

Gravimetric Testers

There are a dozen or more automatic or

semiautomatic gravimetric testers available commercially. All have a small oven with attached or built-in

weighing devices. Heat from electric heating elements

or infrared bulbs dries the samples in a few minutes

and the weight loss is assumed to be seed moisture

only. Some models have direct moisture read-outs, and

others just supply the data for the operator to use.

This type of moisture tester was also developed primarily for rapid determination in grains, but they are

used for tree seeds in some countries. A list of several

laboratories that use such meters on tree seeds can be

found in Bonner (1977).

MANAGING SEED MOISTURE

Knowing the moisture content of your seed does no

good, unless this knowledge is used to maintain seeds

at the proper moisture. In the case of orthodox seeds,

this usually means monitoring the moisture in cleaned

seeds to know when they are dry enough to be put into

storage. It also means using the proper storage container for each type of seed and storage environment.

In the simplest refrigeration systems, no humidity

controls are used, and relative humidity is always

above 90 percent. Since orthodox seeds must be maintained at low moisture contents during storage, they

must be stored in moisture-tight containers to avoid

absorption of moisture from the atmosphere. Recalcitrant seeds, in contrast, may be stored in unsealed

containers in humid atmospheres.

Humidity control in cold storage is possible, but

expensive. It is common in storage facilities for agricultural seeds, where temperatures are lowered only

to about lo-12°C. In these conditions, where relative

humidity is kept in the 50-60 percent range, orthodox

seeds may be stored in unsealed containers, but recalcitrant seeds must be kept in closed containers to avoid

desiccation.

Seeds exposed to the ambient atmosphere will lose

or gain moisture from the atmosphere depending on

seed moisture content, seed chemical content and the

ambient humidity; eventually, the seed moisture will

attain equilibrium with the storage environment.

These equilibrium moisture contents are relatively

constant for each species, which is useful information

for managers of seed storage facilities. A summary of

the known values for southern tree species (table 3)

shows that orthodox seeds have similar values under

the same conditions, while the recalcitrant acorns

equilibrate at higher moisture contents. True

equilibration for acorns is tenuous, because active respiration produces a slowly decreasing seed weight.

Slight differences may also occur because of chemical

content; starchy seeds will usually absorb more atmospheric moisture than seeds with high lipid content.

Figure T.-An acorn sample ready for drying in a microwave oven.

Note that the dish is in the center of the oven floor.

6
‘Pable 3.-Equilibrium moisture contents for some tree seeds stored at 46°C

Equilibrium moisture content (%)

Common name Species Stored at Stored at

40-55% RH 95% RH

Black cherry Prunus serotina 9

Black walnut Juglans nigra 1 1

Green ash Fraxinus pennsylvanica 8

Loblolly pine Pinus taeda 10

Longleaf pine Pinus palustris 10

Shagbark hickory Carya ovata 10

Shumard oak Quercus shwnardii 13

Sweetgum Liquidambar styraciflua 8

Sycamore Platanus occidentalis 9

Water oak Quercus nigra 1 7

White oak Quercus alba 37

Yellow-poplar Liriodendron tulipifera 10

21

20

23

17

‘ii’

32

20

21

29

50

19

LITERATURE CITED

Association of Official Seed Analysts.

1978. Rules for testing seeds. J. Seed Techn.

3(3):1-126.

Bonner, F T

1972. Measurement of moisture content in seeds of

some North American hardwoods. Proc. Int. Seed

Test. Assoc. 37:975-983.

Bonner, I? ‘I!

1977. Equipment and supplies for collecting, processing, storing and testing forest tree seed. U.S. Dep.

Agric. For. Serv. Gen. Tech. Rep. SO-13, 35 p.

South. For. Exp. Stn., New Orleans, La.

Bonner, F. T

1978. Handling and storage of hardwood seeds. In

Proc., Second Symposium on Southeastern Hardwoods. p. 145-152. U.S. Dep. Agric. For. Serv.,

State and Priv. Forestry, Atlanta Ga.

Bonner, F T., and B. J. Turner.

1980. Rapid measurement of the moisture content of

large seeds. U.S. Dep. Agric. For. Serv. Tree Planters’ Notes 31(3):9-10.

Harrington, J. F

1973. Problems of seed storage. In W. Heydecker

(ed.) Seed Ecology: Proceedings p. 251-263. Pennsylvania State University Press, University Park.

International Seed Testing Association.

1976. International rules for seed testing. Seed Sci.

and Techn. 4:3-177.
Appendix I.- Measurement of seed moisture con1 .

2.

3.

4.

5.

6.

7.

8.

9.

tent by oven drying.

Mix the seed lot well and draw the sample correctly.

Do not expose cold seeds to warm, moist air.

Either draw sample in cold storage and place in

airtight container, or allow seed lot to reach room

temperature before sampling.

Do not touch seeds with your fingers; use spoons

or spatulas.

Use covered containers of glass or noncorrosive

metal with rounded sides at the base. Put no more

than 0.3 g/cm2 of seeds on the dish surface. This

rule can be relaxed when drying cut or broken

pieces of large seeds because of larger air spaces

between pieces.

Seeds larger than 10 mm in diameter or 10 mm in

length must be ground or cut into pieces. Grind so

that 50 percent of the material can pass through a

4 mm mesh sieve, unless the seed is oily or high in

moisture (above around 15 percent). For these

cases, cut or break seeds into pieces no larger

than 5-6 mm in diameter.

Allow oven to regain the drying temperature

(103°C) after inserting samples before starting

the drying time.

Leave a space equal to the diameter of a sample

container between containers during drying.

Allow container and sample to cool in a desiccator

for 30-45 min. before taking dry weight. With

rapid-weigh electronic balances in airconditioned (low-humidity) laboratories, the

cooling step can be skipped if necessary. It takes

about 30 s. for hot samples to absorb moisture

from the air.

‘lbke duplicate sample and treat exactly the

same. For large seeds that are ground or cut, two

samples must be prepared independently for the

duplicates.

Appendix II.-Measurement of seed moisture

content with the Burrows (Dole,

Radson) electric moisture metera.

1 . Mix seed lot well and draw a sample of at least l/2

lb.

2. Do not expose seeds to warm, moist air, as moisture will condense on them. Either draw sample

in cold storage and place in air-tight container, or

allow seed lot to reach room temperature before

sampling.

3. Do not touch seeds with your fingers; use spoons

or spatulas.

4. Weigh proper sample size (see calibration charts).

5. ‘Run Power Switch to “ON” position. Set the red

line on the zero mark of “A” scale and balance the

circuit with the Balance Knob (center the needle

in the Balance Meter).

6. Pour sample into hopper.

7. ‘Run Power Switch to “ON” position again, and

rebalance the circuit by turning the Main Dial.

8. Record “A” Scale reading and consult the proper

calibration chart for the corresponding percentage of moisture.

9. Other procedures are as described in the manufacturer’s manual.

aMention of trade names is solely to identify material used and does

not constitute endorsement or recommendation by the U.S. Dep. of

Agriculture over others not mentioned.
Appendix III.-Calibration data for measuring seed moisture content of some southern and eastern tree

species on a Burrows (Dole or Radson) metera.

Sample Moisture content (%)

Common name sizeb (g) 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0 10.5 11.0 11.5 12.0

142 85 88 90 93

142 86 90 94 98

142 87 90 93 95

85 50 52 53 55

85 47 49 50 52

142 81 84 86 89

142 85 88 92 95

142 81 84 87 91

142 . . . . 64 67 70 74

85 . . . 142 74 ‘ii’ 38 43 47 52

82 86 88 92

85 42 4 4 49 51 54 57

-

76

7 8

78

45

41

76

76

70

79

80

81

4 6

43

78

80

74

. . .

82

83

84

4 8

45

80

82

77

60

34

79

4 6

__-

________________________________________ m&orreadingof‘A’ scale____________________--------------------

Black cherry’ (depulped)

Eastern white pine

Loblolly pine

Longleaf pine (dewinged)

Longleaf pine (winged)

Pond pine

Shortleaf pine

Slash pine

Sweetgum’

SycamoreC

Virginia pine

Yellow-poplar’ (dewinged)

9 6 99 102 105 107 110

104 108 114 119 124 129

98 101 103 106 109 111

57 58 60 62 6 4 66

5 4 56 58 60 62 63

92 96 100 105 110 114

9 9 103 107 112 116 120

9 4 97 100 101 105 108

78 82 86 90 95 100

56 61 65 70 7 4 79

9 6 100 105 110 114 119

60 63 66 70 73 77

*Mention oftrade names is for information only and does not imply endorsement or recommendation by the U.S. Dep. ofAgriculture over others

not mentioned. Unless otherwise noted, data supplied by USDA Forest Service, National Tree Seed Laboratory, Macon, Ga., in cooperation with

Eaton Corporation.

bIf 85-g samples are weighed in hopper, a weight must be added (see manufacturer’s instructions).

‘Banner (1978).

Appendix IV.-Calibration data for measuring seed moisture content of some northern and western species on

Burrows (Dole or Radson) metera.

Common name

Sample

size (g)

Moisture content (%)

6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0 10.5 11.0 11.5 12.0

________________________________________ meter pading of ‘A’ ,y& ______---___.

Alpine fir 142 40 45 50 55 60 66 71 77 83 88 94 100 106

Balsam fir 142 52 55 57 60 62 65 68 72 75 78 83 86 91

Colorado blue spruce 142 78 83 87 92 96 101 106 112 118 126 134 142 150

Douglas-fir 142 52 56 60 63 67 71 75 79 83 87 91 95 99

Englemann spruce 142 79 84 88 94 99 104 109 114 121 128 137 146 150

Grand fir 142 66 71 76 80 85 89 94 98 103 107 112 116 121

Limber pine 142 78 82 85 89 93 97 101 105 109 112 118 122 126

Lodgepole pine 142 73 76 80 84 88 92 96 100 104 108 113 118 122

Norway spruce 142 56 59 61 64 67 71 74 78 82 86 91 95 100

Ponderosa pine 142 79 82 85 88 92 96 100 104 108 113 118 123 128

Red pine 142 76 79 82 84 88 91 94 98 102 106 111 114 118

Scotch pine 142 75 79 83 87 91 96 100 104 108 113 118 122 126

Western larch 142 68 72 74 77 80 83 86 89 92 95 98 101 104

White fir 142 42 47 52 57 62 68 74 79 85 90 96 102 107

White spruce 142 44 47 49 53 56 60 65 70 76 83 92 101 111

“Mention of trade names is for information only and does not imply endorsement or recommendation by the U.S. Dep. of Agriculture over others

not mentioned. Data supplied by USDA Forest Service, National Tree Seed Laboratory, Macon, Ga., in cooperation with Eaton Corporation.

9
Appendix V.- Moisture determination using

home microwave ovens.

Differences in ovens and settings make calibration

of individual ovens necessary. Variation can be reduced by preheating ovens prior to measurement.

1. Draw a sample of at least 10 seeds or fruits.

2. Preheat oven with a dish of water at the center of

the oven floor.

3. While oven is heating, quickly break or cut large

seeds into fragments no larger than one-fourth

the size of the intact seeds. Mix and place an

amount equal to five intact seeds in a tared glass

container. Metal containers cannot be used in

microwave ovens.

4. Record fresh weight to three decimal places.

5. When oven floor temperature reaches 6o”C, remove water dish and place container and sample

in center of oven.

6. Dry sample for selected time period. While the

first sample is drying, draw, prepare and weigh a

duplicate sample in the same manner. Check

floor temperature before drying second sample (it

should be 60°C).

7. Remove sample and weigh immediately on electric pan balance. If a rapid-weigh balance is not

available, samples should be cooled in a desiccator for 30-40 min before weighing.

Appendix VI.- Typical drying times using General Electric JET 85, OT 1” Microwave

oven at low setting (floor temperature, 60°C).

Common name Species

Sample

weight (g)

__~

Sample Drying

condition time (min)

Green ash Fraxinus pennsylvanica 3

Shagbark hickory Carya ovata 20

Shumard oak Quercus shumardii 25

Water oak Quercus nigra 10

White ash Fraxinus americana 3

intact 5

broken 4 %

cut 4 %

cut 4 %

intact 5

“Mention of trade names is solely to identify material used and does not constitute endorsement or recommendation

by the U.S. Dep. Agriculture over others not mentioned.

10
BONNER, F T

1981. Measurement and management of tree seed moisture.

U.S. Dep. Agric. For. Serv. Res. Pap. 50-177, 10 p. South.

For. Exp. Stn. New Orleans, La.

There are two kinds of tests for routine measurement of tree

seed moisture, (1) accurate measurement (such as official

International Seed Testing Association tests) and (2) rapid

estimates.

Additional keywords: seed storage, moisture meters, hardwood, conifers.

*U.S. GOVERNMENT PRINTING OFFICE: 1981--569~082/16 11