On March 23, 2026, the USDA Agricultural Marketing Service (AMS) published a proposed rule to update the National Organic Program's (NOP) National List of Allowed and Prohibited Substances. The proposal would permit the use of synthetic carbon dioxide in organic crop production under specific conditions.
The National List defines which synthetic substances are allowed—and which natural substances are prohibited—under the National Organic Program. Under the Organic Foods Production Act of 1990, synthetic inputs can only be approved if they meet strict criteria and are recommended by the National Organic Standards Board (NOSB).
Two proposed uses
The rule reflects NOSB recommendations from 2022 and 2024 and proposes adding carbon dioxide in two areas:
- Irrigation water treatment (7 CFR 205.601(a))
Synthetic carbon dioxide would be allowed to adjust irrigation water pH, helping prevent mineral buildup and clogging in irrigation systems. - Indoor crop production (7 CFR 205.601(j))
Carbon dioxide—restricted to byproduct sources—would be permitted for atmospheric enrichment in greenhouses and other indoor growing systems, as well as for optimizing irrigation water pH for nutrient availability.
Greenhouse relevance
The proposal is particularly significant for greenhouse growers. The NOSB highlighted that optimal CO₂ levels (800–1,000 ppm) are essential for plant growth in controlled environments, where crops quickly deplete available CO₂. Supplementation is often necessary, especially in colder climates where ventilation is limited.
Sustainability and safety considerations
According to AMS and NOSB, the use of captured, byproduct CO₂ is considered environmentally neutral, as it repurposes emissions that would otherwise be released.
CO₂ is already approved for use in organic processing and is widely recognized as safe by U.S. regulators, including the FDA and EPA. Compared to alternatives such as sulfur burners, CO₂ is safer for workers and less hazardous in irrigation systems.
Limited alternatives
Both AMS and NOSB concluded that natural CO₂ sources are not commercially viable at scale, and existing alternatives for pH control or greenhouse enrichment are either less effective or pose greater risks.
Call for feedback
AMS is inviting public comments on several aspects of the proposal, including the necessity of synthetic CO₂ for the proposed uses, whether restrictions to byproduct sources should also apply to irrigation use, the availability of alternative substances or practices.
If finalized, the rule would expand tools available to organic growers—particularly in greenhouse production—while maintaining compliance with organic standards.
Source: https://www.federalregister.gov/
