Guano

How does OMRI review guano as a crop fertilizer, and when does it carry a restriction?

By Gwynn Sawyer Ostrom

Guano is a naturally occurring substance primarily made from the excrement of wild bats and birds. It is commonly used as a fertilizer and is typically high in nitrogen, phosphate and potassium (NPK). It can be found where colonies of seabirds dwell, such as islands near coasts and subtropical latitudes where there is little rain, or in caves. In some places, guano goes through a lengthy process of mineralization over many thousands of years with the help of temperature, and humidity. Additionally during this period, the guano is slowly decomposed by the action of bacteria and other microorganisms, changing it from an organic to an inorganic form (minerals, soluble and insoluble compounds).

OMRI considers completely mineralized guano, which is then collected, to be a mined mineral. Guano that is not completely mineralized is considered raw manure and, if it is not: a) further processed in accordance with National Organic Program (NOP) Guidance 5006, or b) composted according to §205.203(c) of the NOP regulations, it will carry the “days to harvest” restriction when reviewed to NOP regulations. The “days-to-harvest” restriction ( §205.203(c)(1)) specifically states that raw manure can only be, “Applied to land used for a crop not intended for human consumption,” or “Incorporated into the soil not less than 120 days prior to harvest of a product whose edible portion has direct contact with the soil surface,” or “Incorporated into the soil not less than 90 days prior to harvest of a product whose edible portion does not have direct contact with the soil surface.”

For products reviewed to Canada Organic Regime (COR) standards, there is no days-to-harvest restriction, and guano products listed to COR do not carry a restriction; the only requirement is that the product consists of decomposed, dried deposits of wild bats or birds (CAN/CGSB-32.311-2015). As a reminder, OMRI listing does not guarantee that a product meets all applicable legal requirements at the state, provincial or federal level (OMRI Policy Manual© §1.8).

Guano that is further treated, either composted or heated and dried to meet the processed manure standards, may be reviewed for OMRI listing under a Compost or Processed Manure category.

This article first appeared in the summer 2017 issue of the OMRI Materials Review newsletter, and was revised and updated in September 2019 by Senior Technical Coordinator Peter Bungum.