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Effect of CO2 on soybean maturity in the greenhouse

Principal Investigator: Kangfu Yu and Jamie Larsen

Research Institution: Agriculture and Agri-Food Canada (AAFC)

Timeline: April 2020 – March 2023   


  • To study the effect of CO2 on soybean maturity in the greenhouse.
  • To reduce soybean maturity date with higher concentration of CO2.
  • To speed up generation advancement in the greenhouse.


  • Speed up the breeding process for the development of soybean varieties for Canadian growers.
  • Decrease the spending of research funds for winter nursery.

Scientific Summary:

The slow generation times of soybean plants are currently a major hinderance to soybean breeding. Usually, breeders will use a winter nursery in South America to accelerate the generation advance. The use of a greenhouse can also help to advance the crop during winter. Unfortunately, it takes 4-5 months for soybeans to mature in the greenhouse under normal conditions. However, it was reported that supplementation of CO2 can reduce the maturity date of soybean from 102 – 132 to 70 days in a growth chamber. The objective of this study was to increase the CO2 concentration in the greenhouse to study the effect of CO2 on soybean maturity.

The initial plan was that in October or November of each year, CO2 would be supplied to the greenhouse to reach a concentration of 750 ppm in 2020 and 850 ppm in 2021 and 1000 ppm in 2022. Plant growth and maturity would be recorded and compared to see the effect of higher CO2 on soybean maturity. The best concentration of CO2 would then be identified under greenhouse conditions to reduce the maturity date from around 130 days to approximately 70 days so that two generations could be advanced in the greenhouse. Unfortunately, the COVID pandemic severely limited access to the greenhouse during the first two years of the project and the above plan was not able to be fully carried out.

In 2022-2023 COVID restrictions were lifted, and the project resumed exploring CO2 supplemented vs CO2 ambient treatments across three varieties of soybean in the greenhouse at AAFC Harrow.


The results found that CO2 supplementation (1200 ppm) significantly increased the number of days to maturity, on average, by 4.7 days relative to ambient atmospheric CO2 levels (500 ppm). Thus, the hope for a days-to-maturity reduction down to approximately 70 days did not happen. All the varieties behaved similarly with a significant increase in maturity associated with CO2 enrichment. There was a significant increase in yield for the soybean plants under CO2 enrichment (367% on average or approximately 70 seeds per plant) compared to the ambient CO2 treatment. Both of these trends have been previously noted in the research literature.

These results are significant given that breeders are limited in seed productivity of plants grown indoors, which limits population size and the number of progeny that can be evaluated and selected from the population. Increased seed production also impacts the amount of testing that can be done in trials or nurseries in the following generation. All of this improves the chances of selecting and releasing improved varieties for Ontario soybean farmers.

Immature pods were also collected from plants and examined as an option to speed up generation advance. The germination was reasonable from these harvested pods indicating that this method of harvesting pods early, coupled with CO2 enrichment, could be a faster method to productively speed generation advance in soybean breeding.

In conclusion, CO2 enrichment in greenhouses was found to increase seed yield, and plants grown in a greenhouse on station (as opposed to a field in South America) means breeders can accelerate breeding cycles by picking pods early. This has the potential to impact how the breeding program at AAFC-Harrow functions. Previously, significant financial resources were placed on completing generation advance in winter nurseries. The results of this project will now allow the program to remove that cost (~$10K – $20K / year) and possibly achieve the same results (or even advance an extra generation indoors), giving rise to the potential of reducing the time from initial cross to variety release by one year. Given that soybean and pulse breeding programs are often limited by seed multiplication, increased seed production in the greenhouse will translate to more plants in the field and increased potential to do more testing thereby improving selection of soybean lines being developed and released to Ontario farmers.

External Funding Partners:

Ontario Soybean & Canola Committee

Project Related Publications: