The oxygen deprivation caused by partial vacuuming or the replacement of air in hermetic enclosures with dinitrogen, CO₂ or a mixture of the two inert gases, has the effect of prolonging the longevity (viability) of seeds. Numerous published studies on the long-term storage of oilseeds and protein crops (such as soybeans) have shown that there is a significant advantage to storing in a rarefied oxygen atmosphere, either under vacuum, or by replacing the air with inert gases, even partially.
If, in addition to oxygen depletion, carbon dioxide (CO₂) is added, the beneficial effect is even more pronounced, whatever the residual oxygen content, provided that the CO₂ content is greater than or equal to 50%.
Pulses (chickpeas)
Storage in CO₂ atmospheres at over 50% air concentration significantly prolongs seed viability, even when seed temperatures exceed recommended limits to limit the degrading effect of high temperatures.
For example, after 6 months' storage of chickpeas in hermetically sealed containers under 50% CO₂, the germination percentage remained at 89.2%, compared with 74.5% when stored in the open air.
Rice (and similar cereals)
By storing rice in a 50% CO₂ atmosphere at elevated temperature for 45 days, germination capacity is maintained at 95-97% depending on variety, compared with 79-81% when stored in the open air. The effect on the germination vigor index is even more significant: the index drops to 83-94% of its initial value under CO₂, whereas it falls to 60-67% of its initial value in the open air (under the effect of the high temperature).
Soy
Thus, for soybeans stored at room temperature (fluctuating seasonally between a minimum of 14.5°C and a maximum of 35.7°C), when kept in the open air, germination capacity falls from 95.3% to just 19.4% after one year's storage. When stored under the same temperature conditions in hermetically sealed containers in an atmosphere with a CO₂/O₂/N₂ composition of 80/5/15%, it retains a germination capacity of 82.5% after one year. Under vacuum in a sealed polyethylene bag, germination is 81.2%, and under pure CO₂, 74.3% (figure 21).
If the storage temperature had not exceeded 22°C at the start of the (hottest) storage period, it is likely that germination capacity would have been fully preserved with the most "conservative" modified atmosphere composition: only 5% O₂ and 80% CO₂, the remainder nitrogen (15%). This advantage of inert gas conservation is particularly important for the long-term conservation of oilseed and protein crop seeds.
This advantage of conservation under CO₂-enriched atmosphere has been verified by other authors (figure 22 of Capilheira et al, 2019).