I have only been able to find one source of dry molasses in this area, sold as animal feed. However, the ingredient list includes propionic acid as a preservative. I want to use this as an organic fertilizer/amendment, but I don't know how it will affect the soil microbiology I'm trying to build up. Does anyone have any experience or advice with this type of product?

where do you live?

Prescott Valley, AZ

You might want to get a hold of the Native plant society in your area and see if they have a recommendation for an organics outlet in your area.

http://www.aznps.com/sources.html

You can easily purchase liquid horticulture grade molasses from this site or other sites on the internet.