What’s that smell? What materials can I use to neutralize the odors in my organic fertilizers?

by Brice Crayne

Organic farming often depends on some smelly products, such as manure and fish emulsion, for several functions such as increasing soil fertility, reducing municipal wastes and supporting animal waste management. What is it that makes these materials unappealing to our sense of smell? Ammonia (NH₃) and methane (CH₄) are two of the most common compounds emitted during the microbial breakdown of organic compounds that are instinctually unappealing to humans. Imagine a barn with 10,000 laying hens…that’s a lot of poop! Facilities like these generally have conveyors that continuously remove excrement to compost piles. But are there any allowed materials that could be used to neutralize the NH₃ and CH₄ compounds that are so potent to our senses?   

The most important thing to consider when researching potential materials to reduce odors is the final use of the product (manure, compost feedstocks or fish emulsion). For example, odor control substances added to manure that will be composted and used on organic fields must be allowed by the National Organic Program (NOP) for the product to be compliant. This means the additives need to be nonsynthetic or listed as an allowed synthetic compost feedstocks at §205.601. OMRI lists ”Odor Control Products” under the Crop management tools and production aids (CT) Class and the Livestock management tools and production aids (LT) Class depending on the intended use of the odor control product. 

Nonsynthetic adsorbent materials such as zeolite and attapulgite (a type of clay) have been successfully proven to reduce the amount of NH₃ released into the air. Other materials that consistently reduce ammonia emissions include essential oils of Hyssopus (hyssop) and Mentha (peppermint), iron-rich sediments, certain microbial products, and wood chips used as a carbon-cover. All of these materials are allowed in their nonsynthetic forms. Clays are mined materials and allowed at §205.203(d)(2). Essential oils are allowed when extracted from a natural source and meet all other criteria in NOP Guidance 5033-1. Wood chips are inherently nonsynthetic but cannot contain plywood, pressboard, or treated, painted or stained wood.  

Some of the most common odor-reducing materials are synthetic and therefore prohibited for use in organic farming. Soaps and detergents are commonly applied in odor reduction management and would not be allowed as an odor control substance in organic production. Another common synthetic product used to neutralize odors is superphosphate (monocalcium phosphate), which is not allowed in organic production systems.  

The rule of thumb when it comes to organic input materials, whether you are trying to keep the smelly odors down in your barn or increase the nutrient value of your compost, is use nonsynthetics, many of which are OMRI Listed. Organic producers should check with their certifier before using any new materials.

Revised and updated in March 2019 by OMRI Technical Director Doug Currier. This article was originally published in the Summer 2014 edition of the OMRI Materials Review newsletter.