On January 24, 1978, four USDA agencies - Agricultural Research Service (ARS), Cooperative State research Service (CSRS), Extension Service (ES), and the National Agricultural Library (NAL)- merged to become a new organization, the Science and Education Administration (SEA), U.S. Department of Agriculture.
This publication was prepared by the Science and Education Administration's Federal Research Staff, which was formerly the Agricultural Research Service.
Library of Congress Catalog Card No. 78-600015
Washington, D.C. Issued April 1978
For sale by the Superintendent of Documents, U.S. Government Printing Office
Washington, DC 20402
STOCK NUMBER 001-000-03653-0
Principles and Practices of Seed Storage
Page 57
Vacuum and Gas Storage
For many years research has been conducted on the effects of a partial vacuum and such gases as carbon dioxide, oxygen, and nitrogen on the longevity of various kinds of seeds. The reported results from these studies are variable and in some instances appear contradictory. This confusion undoubtedly results from the widely divergent test methods employed by the various researchers. Because of the lack of complete information on the test procedures used in numerous studies, direct comparisons cannot be made between and among the various data found in the literature. Likewise sealed storage cannot be directly compared with open storage, because in sealed containers oxygen concentration in the atmosphere decreases and the carbon dioxide concentration increases with time (Harrington, 1963) whereas in open storage the composition of the atmosphere remains constant. Because it is not feasible to continually adjust the composition of the atmosphere in sealed containers, most studies have not included gas analyses. Some workers paid no attention to either seed moisture or storage temperature, whereas others attempted to control one or the other. Several used air-dry seeds and room temperature, both of which provide a minimum of information about the conditions actually used. Regardless of the kind of seed, the air-dry moisture content in one geographic area is not necessarily the same as that in another. Likewise room temperature is not consistent from place to place nor from month to month, or even from day to day in most localities. To accurately assess the protective value of either a partial vacuum or a gas, all environmental conditions have to be considered. Reports on a few kinds of seeds will illustrate the variable results in the literature.
Barley
The higher the oxygen content of the storage environment, the shorter the viability period for barley seeds (Roberts and Abdalla, 1968) The deleterious effects of oxygen are produced at relatively low oxygen concentrations and are most pronounced at the higher seed moisture levels.
Corn
Since the seedsman wants to store his seeds at the highest practical moisture level and temperature, Goodsell et al. (1955) stored seed of two corn hybrids at approximately 8, 10-, 12- and 14-percent moisture sealed in air, carbon dioxide, and nitrogen at approximately -18°, 4°, 16°, and 29° C. Generally the average pooled germination of the two...
(Text continued after the following table on page 61.)
Tables 12 and 13 on pages 58-60
Principles and Practices of Seed Storage
Page 61
TABLE 14. Germination of aster seeds after storage at 12 temperature-moisture conditions over 36 months1
Germination at indicated seed moisture
content (percent)
Months Temperature 4.6 6.1 7.9 Ambient
'C Percent Percent Percent Percent
6 -5 90 88 85 87
5 87 88 90 72
Room 89 84 85 86
12 -5 87 88 87 86
5 91 90 91 64
Room 90 83 83 83
18 -5 85 79 87 82
5 83 80 84 46
Room 78 78 60 71
24 -6 66 71 68 72
5 68 71 56 4
Room 64 35 O 3
30 -5 84 86 85 82
5 84 87 87 O
Room 75 33 O 15
36 -5 90 92 91 86
5 91 93 89 O
Room 76 9 O O1Data from Buton (1539). Seeds stored at room temperatures were sealed in glass tubes; all others were sealed in tin cans; average germination at start of experiment assumed to be 90-92 percent.
...hybrids in the three storage gases was still 95 percent or better after 5 years for the seeds at 8-, 10-, and 12-percent moisture at -18° and 4° and those containing 8- and 10-percent moisture at 16°. Seeds containing 12- or 14 percent moisture at 16° and those with 8- and 10-percent moisture at 29° degrees deteriorated rapidly after 1 year. Corn seeds containing 12- to 14-percent moisture were practically all dead after one-half to 1 year, regardless of the surrounding gas.
Sayre (1940) stored corn seeds with 18 percent moisture in oxygen, carbon dioxide, and nitrogen at 30° C. The seeds in oxygen died within 3 years and the germination of the seeds in carbon dioxide and nitrogen dropped noticeably. At low temperatures corn seeds with 18 percent moisture sealed in carbon dioxide and nitrogen had good germination for 5 years.
Struve8 dried corn seeds to near 0-percent moisture, sealed them in oxygen and in nitrogen, and stored them at -30° to 50° C. Seeds at -30°...
Footnote8: Struve, W. M. Drying and Germinability of Maize. 1958. [Unpublished Ph.D. thesis. Copy on file Dept. of Botany, Iowa State Univ., Ames.]
Principles and Practices of Seed Storage
Page 62
...remained unchanged through 31 months, those at 50° in nitrogen showed a progressive reduction in vigor, and seeds in oxygen died within 7 months. He also stored corn seeds with 1-percent moisture content in atmospheres containing 0-, 20-, 60-, and 100-percent oxygen at 0°, 5°, 10°, 15°, 25°, 35° and 50°. He concluded that oxygen concentration may become an important factor in the deterioration of corn seeds in sealed storage.
Flower Seeds
Primula sinensis sealed in carbon dioxide declined only 30 percent in viability over 7-year period, whereas unsealed seeds lost all viability (Lewis, 1953). Seeds of salvia splendens deteriorated seriously when sealed under a vacuum (Chopinet, 1952) Aster seeds kept equally well when sealed in air or a partial vacuum (Barton, 1939). Sealing under a partial vacuum had no advantage over sealing in air for maintaining the viability of verbena seeds (Barton, 1939).
Barton (1960a) stored seeds of Lobelia cardinalis with 6.9- and 4.7-percent moisture in sealed glass vials in air, oxygen, carbon dioxide, nitrogen, and vacuum and in open containers for up to 25 years at laboratory temperature, 5°, and -5° C. In all eases, viability was lost more rapidly at laboratory temperature than at 5° and -5° and at 6.9 percent than at 4.7-percent moisture. At laboratory temperature, 6.9-percent moisture seeds in air, open or sealed, lost viability rather rapidly. Seeds sealed in oxygen lost viability even more rapidly, whereas carbon dioxide, nitrogen, and a partial vacuum extended the life of the seeds for 6 to 8 years. When seed moisture was reduced to 4.7 percent, seed longevity was increased at laboratory temperature. Carbon dioxide, nitrogen, and vacuum were superior to air and oxygen, with oxygen causing the most rapid deterioration. There were no significant differences in the response of seeds to atmospheres of carbon dioxide, nitrogen, or under vacuum at room temperature or to air, oxygen, carbon dioxide, nitrogen, or vacuum at 5° and -5° except those resulting from increased time in storage.
Grasses
The effect of nitrogen was negligible on the longevity of Chewings fescue (Gane, 1948a) and meadow fescue (Evans et al., 1958). There was no advantage in using either nitrogen or a partial vacuum rather than air for sealed storage of seeds of Kentucky bluegrass and creeping red fescue (Isely and Bass, 1960). In fact, when the seeds were subjected to an unfavorable temperature, loss of viability was more rapid for seeds packaged with nitrogen or under vacuum than with air.
Principles and Practices of Seed Storage
Page 63
Legumes
Seeds of both red and white clover stored under vacuum and in nitrogen were shorter lived than those stored unsealed (Davies, 1956). Red clover seeds containing 10.3-percent moisture when sealed with carbon dioxide lost all viability in 23 years, but when calcium chloride was used with the carbon dioxide, only about one-third of the initial viability was lost (Evans, 1957a).
No atmosphere tested, including air, vacuum, carbon dioxide, nitrogen, helium, and argon, was consistently or significantly better than all others for 2 years of sealed storage of crimson clover seeds (Bass et al., 1963a).
Oilseeds
Soybeans in open storage for nearly 6 years lost viability (Guillaumin, 1928), whereas seeds sealed in an atmosphere free of oxygen germinated 92 percent and those under a vacuum had 100-percent viability.
Low moisture (7 percent) cottonseeds retained their initial viability when sealed in air, oxygen, carbon dioxide, or nitrogen and stored at 21° and 32° C (Simpson, 1953). Seeds with 13-percent moisture dropped to one-half to two-thirds of the original germination under all storage conditions. The loss of germination with oxygen was no greater than with carbon dioxide or nitrogen; however, the loss in air was greater than in the pure gases.
Bass et al. (1963b) found that air, vacuum, carbon dioxide, nitrogen, helium, or argon was neither consistently nor significantly better than the others for sealed storage of safflower and sesame seeds for 2 years.
Rice
Much of the literature pertains to the storage of rice seeds for both food and seed. In areas where rice is grown, seed moisture content tends to remain high even when the seeds are air-dry. Deterioration of high moisture (20.8 percent) seeds at 30° C can be delayed for a few weeks by sealing them in an atmosphere of carbon dioxide mixed with 1,000 p/m of ethylene oxide (Kaloyereas, 1955).
Kondo and Okamura (1927, 1929, 1930, 1934) and Kondo et al. (1929) found that both rough and hulled rice can be stored sealed with carbon dioxide or air for up to 4 years with little loss of viability provided the seed moisture content is less than 13 percent. They reported that carbon dioxide had a slight advantage over air. Rice dried to 5-percent moisture and sealed in an atmosphere of nitrogen germinated 99 percent after 8 years, but with 13-percent moisture all viability was lost (Sampietro, 1931). Seeds with either 5- or 13-percent moisture lost all viability when sealed in carbon dioxide, air, or under a partial vacuum.
Principles and Practices of Seed Storage
Page 64
Sorghum
Sorghum seeds during the second year of storage retained significantly higher germination when sealed under a partial vacuum than when sealed in air, carbon dioxide, nitrogen, argon, or helium (Bass et al., 1963a).
Vegetable Seeds
For pea seeds the period of safe storage decreased as the oxygen concentration in the storage atmosphere increased from 0 to 21 percent (Roberts and Abdalla, 1968). The deleterious effects of oxygen were more pronounced at the higher seed moisture contents. There was no advantage in using sealed storage under nitrogen or a partial vacuum rather than air for onion seeds (Gane, 1948b; Isely and Bass, 1960). However, seeds sealed in carbon dioxide retained their viability better than did similar seeds sealed in air (Lewis, 1953; Harrison and McLeish, 1954; Harrison, 1956). Vacuum, carbon dioxide, nitrogen, helium, and argon storage had no advantage over sealed-in-air storage for lettuce seeds during 2 years (Bass et al., 1962). Although lettuce seeds sealed in carbon dioxide retained their viability better at room temperature than did similar seeds sealed in air, storage in carbon dioxide revealed differences in longevity between cultivars (Harrison and McLeish 1954; Harrison, 1956).
Cabbage seeds stored equally well when sealed in air, nitrogen, or a partial vacuum (Isely and Bass, 1960). Parsnip seeds retained their viability better when sealed in carbon dioxide than in air (Lewis, 1953; Harrison, 1956). Dandelion seeds retained their viability about equally well when sealed in a partial vacuum or in air, except seeds containing 7.9-percent moisture seemed to deteriorate more rapidly in a partial vacuum (Barton, 1,939).
Wheat
Wheat, like rice, is an important food crop, which has received much attention because the condition of storage greatly affects its milling and processing qualities as well as its seed germination. To improve the storage of wheat seeds for both planting and food purposes, studies have been made on the effects of nitrogen and carbon dioxide on seed viability. Loss of viability of high moisture wheat seeds can be delayed for several days by sealing under either 50 or 75 percent of carbon dioxide (Peterson et al., 1956) or nitrogen (Glass et al., 1959). However, once deterioration starts, it proceeds rapidly. It can be delayed for several additional weeks by combining nitrogen storage with a lower temperature (20° C); however, even this combination is unsatisfactory for extended storage.
Principles and Practices of Seed Storage
Page 65
Confirmation Studies at the National Seed Storage Laboratory
Obviously some kinds of seeds under certain circumstances are benefited by vacuum or gas storage. The question then is "Under what conditions is vacuum or gas storage practical and desirable?" To more fully understand the interrelationship involved, a comprehensive study was undertaken at the National Seed Storage Laboratory, Fort Collins, Colo. One lot each of the following kinds of seeds was adjusted to 4-, 7-, and 10-percent moisture and sealed in air, under vacuum, and in carbon dioxide, nitrogen, helium, and argon and stored at -12°, -1°, 10°, 21°, and 32° C: 'Dixie' crimson clover, 'Great Lakes' lettuce, 'Pacitic No. 1' safflower, 'Margo' sesame, and 'RS 610' hybrid sorghum. No gas analyses were made after storage. Germination tests were made at the time of storage and at intervals thereafter. Because commercially available equipment was very expensive, Bass and James (1961) developed a simple, inexpensive device for vacuum and gas sealing of tin cans. The complete sealer (fig. 5 [and not shown]) consists of a vacuum chamber, soldering gun, three-way valve, vacuum gage, several lengths of air hose, hose clamps, a brass tee fitting, and a source for both vacuum and gas.
Germination tests were made in electronically controlled water-curtain germinators operated at 20° C for crimson clover and lettuce and a 20° to 30° night-to-day alternation for safflower, sesame, and sorghum. Each test consisted of two 100-seed replicates planted according to official procedures (Association of Official Seed Analysts, 1954) except safflower, for which official procedures had not been developed at that time. Safflower was planted the same as sorghum. In all tests only normal seedlings - those capable of producing plants - were recorded. For crimson clover, which has hard seeds, the percentage of hard seeds was added to the percentage of normal seedlings to give total germination.
Principles and Practices of Seed Storage
Page 66
The data (table 15) show that regardless of the kind of seed, no storage atmosphere consistently gave the highest germination percentage at all temperatures for seeds of all moisture levels tested. The data also show that there are distinct differences between kinds of seed in their response to temperature and seed moisture content. Of the five kinds of seeds, sorghum showed the least sensitivity to the interaction between seed moisture content, storage temperature, and storage atmosphere (table 15). Only the 10 percent moisture seed showed really drastic germination reductions when stored at 32° C. At that temperature seeds in all atmospheres except those under a partial vacuum (3 percent) and in argon (5 percent) were completely dead. At 21°, seeds with 10-percent moisture in a partial vacuum, helium, and argon did not show a significant reduction in germination, but seeds in all other atmospheres did. Significant reductions in germination were recorded for 4-percent moisture seeds under vacuum at 21° and in air, nitrogen, and helium at 32°. Significant reductions in germination occurred for 7-percent moisture seeds in all atmospheres at 32°. No significant reductions were recorded for seeds of any moisture content in any atmosphere at 10°, -1°, and -12° C.
Crimson clover seeds (table 15) stored in paper envelopes (check) showed a significant decrease in germination after 8 years of storage at each temperature for each initial moisture level except 4- and 10-percent moisture seeds held at -12° C. Except for 7- and 10-percent moisture seeds at 10°, 21° and 32°, only an occasional sample of sealed seeds showed a significant decline in germination. Such declines were not consistent for storage temperature, seed moisture, or surrounding atmosphere. A significant decline in germination of sealed seeds stored at -12° was recorded for 7-percent moisture seeds in a partial vacuum and for 10-percent moisture seeds in air. At -1°, significant germination losses occurred with 7-percent moisture seeds held in nitrogen and with l0-percent moisture seeds held in air, vacuum, carbon dioxide, nitrogen, and helium. The significant germination declines recorded at 10° occurred for 7-percent moisture seeds in air, carbon dioxide, and nitrogen and for 10 percent moisture seeds in air, vacuum, carbon dioxide, nitrogen, and helium. At 21°, significant decreases occurred for 7-percent moisture seeds in air, carbon dioxide, nitrogen, and helium and for all 10-percent moisture seeds.
The only significant decrease in germination of 4-percent moisture seeds held at 32° C was for those in nitrogen. All 7-percent moisture seeds showed a significant decline, with the highest germination maintained in an atmosphere of argon. Argon also gave the highest germination of 4-percent moisture seeds at 32°.
The sealed 10-percent moisture seeds at 32° C showed a significant decline in germination the first year of storage and germinated 12
Table 15 on pages 67-70
Principles and Practices of Seed Storage
Page 71
percent or less at the end of the second year. By the end of the eighth year, even the few hard seeds initially present were dead.
Maximum germinations were distributed among atmospheres as follows:
Atmosphere
and
Combinations Seed Moisture Tempera-
(number) (percent) ture (C)
Air (1) 4 32
Vacuum (3) 7 10
21
10 -12
Carbon Dioxide (2) 7 -12
10 21
Nitrogen (2) 4 -1
7 -12
Helium (4) 4 -12
21
32
7 -1
Argon (6) 4 10
32
7 10
32
10 -1
10In some tests the same germination was recorded for seeds in two or more atmospheres. This finding applies to the tabular data for lettuce, safflower, sesame and sorghum (pp. 72-74).
The data for lettuce (table 15) show that seed moisture and storage temperature had more effect on germination than did the composition of the surrounding atmosphere. Drying to 4-percent moisture before sealing made possible the storing of lettuce seeds at as high as 32° C with significant differences between atmospheres evident only at 32°. The apparent significant decline to 5-percent germination for 4-percent moisture seeds in a partial vacuum at 10° resulted from a defective seal after evacuation. The 1-percent germination for 7-percent moisture seeds in air at 10° also resulted from a defective seal. In both tests a fine hole in the solder allowed the seeds to absorb moisture from the atmosphere until an unsafe level was reached. These data emphasize the need for extreme care in sealing seed containers. Highest germination of lettuce seeds in sealed cans occurred as follows:
Principles and Practices of Seed Storage
Page 72
Atmosphere
and
Combinations Seed Moisture Tempera-
(number) (percent) ture (C)
Air (2) 4 -12
7 -12
Vacuum (3) 4 -12
-1
10 -12
Carbon Dioxide (2) 4 32
7 -1
Nitrogen (4) 4 10
7 -1
10
10 -1
Helium (2) 4 -12
32
Argon (3) 4 10
21
10 -12...Safflower seeds must be dried to 4-percent moisture (table 15) for safe, sealed storage at ordinary temperatures regardless of the surrounding atmosphere. Seeds containing 7-percent moisture cannot be stored safely above 10° C, and 10-percent moisture seeds cannot be stored above -1°. All sealed 10-percent moisture safflower seeds showed a significant loss in germination during 8 years of storage. The array of highest germinations for safflower seeds sealed in various atmospheres were as follows:
The following table spans pages 72-73
Atmosphere
and
Combinations Seed Moisture Tempera-
(number) (percent) ture (C)
Air (2) 7 -1
10
Vacuum (0) --- ---
Carbon Dioxide (4) 4 -12
10
32
10 -1
Nitrogen (3) 4 -12
7 -12
10 -12
Helium (1) 10 -1
Argon (2) 4 -1
21Principles and Practices of Seed Storage
Page 73
The data for sesame seeds (table 15) show that this oilseed does not store well when sealed in any atmosphere at moisture levels above 7 percent unless the temperature is kept at -1° C or lower. For sealed storage in any atmosphere at higher temperatures seed moisture content must be reduced to 4 percent. The distribution amount atmospheres of the highest germination percentages for sesame seeds was as follows:
Atmosphere
and
Combinations Seed Moisture Tempera-
(number) (percent) ture (C)
Air (1) 7 -1
Vacuum (0) --- ---
Carbon Dioxide (4) 4 -12
32
7 -12
-1
Nitrogen (2) 4 -12
-1
Helium (2) 7 -1
10
Argon (2) 4 10
21No atmosphere was consistently better than all others for preserving the germination of sealed sorghum seeds. Therefore it is interesting to note that among seed moistures and storage temperatures the following combinations, with atmospheres that gave the highest germinations after 8 years of sealed storage, were about equally divided:
The following table spans page73-74
Principles and Practices of Seed Storage
Page 74
Atmosphere
and
Combinations Seed Moisture Tempera-
(number) (percent) ture (C)
Air (4) 4 -1
7 -1
10
10 10
Vacuum (4) 4 -12
-1
7 32
10 -1
Carbon Dioxide (3) 4 -1
21
7 21
Nitrogen (3) 4 -12
10
10 -12
Helium (2) 4 -1
7 -12
Argon (5) 4 -12
32
7 10
10 21
32...The distribution of highest germinations for all five kinds of seeds among the various atmospheres in sealed metal cans is summarized as follows:
[The last table runs through pages 74-76]
Atmosphere
and
Combinations
(number), and Seed Moisture Tempera-
kind of seed (percent) ture (C)
Air (10)
Crimsom Clover 4 32
Lettuce 4 -12
7 -12
Safflower 7 -1
10
Sesame 7 -1
Sorghum 4 -1
7 -1
10
10 10
-----------------------------------
Vacuum (10)
Crimsom Clover 7 10
21
10 -12
Lettuce 4 -12
-1
10 -12
Sorghum 4 -12
-1
10 -12
-----------------------------------
Carbon Dioxide (3)
Safflower 4 -12
10
32
10 -1
Sesame 4 -12
32
7 -12
-1
Sorghum 4 -1
21
7 21
-----------------------------------
Nitrogen (14)
Crimson Clover 4 -1
7 -12
Lettuce 4 10
7 -1
10
10 -1
Safflower 4 -12
7 -12
10 -12
Sesame 4 -12
-1
Sorghum 4 -12
10
10 -12
-----------------------------------
Helium (2)
Crimson Clover 4 -12
21
32
7 -1
Lettuce 4 -12
32
Safflower 10 -1
Sesame 7 -1
10
Sorghum 4 -1
7 -12
-----------------------------------
Argon (18)
Crimson Clover 4 10
13
7 10
32
10 -1
10
Lettuce 4 10
21
10 -12
Safflower 4 -1
21
Sesame 4 10
21
Sorghum 4 -12
32
7 10
10 21
32It is obvious from this distribution of highest germinations that no one atmosphere is decidedly better than the others for safe, sealed storage of seeds.
The data in table 15 show that regardless of the kind of seeds or the atmosphere in the sealed container, only adequately dried seeds (4-percent moisture) retained their germination reasonably well during 8 years of storage at 32° C. Some kinds did not keep well at 21°, and sesame seeds with 7- and 10-percent moisture lost all viability at 10° except for 1 or 2 percent when sealed in helium or argon.
It is obvious from the data that seed moisture content at the time of sealing has a far greater effect on seed longevity than does the surrounding atmosphere. For most situations the added expense of using an atmosphere other than air appears unnecessary. However, even for
Principles and Practices of Seed Storage
Page 77
sealing in air, most kinds of seeds require additional drying before sealing if the sealed seeds are to be subjected to a temperature above 10° C. In general, the added advantage, if any, of an atmosphere other than air is not realized except during very long term storage.
End of Vacuum and Gas Storage Section.