When muck becomes stuck - figuring out residual nutrients from your organic matter applications

Wednesday, January 11, 2023

 As we’re in the midst of planning for the coming season and reassessing potentially fool-hardy plans made with the best intentions but rosiest of glasses, I wanted to write a quick post to touch on the idea of compost/organic matter amendments and the residual nutrient credits they provide year after year.

Organic amendments such as composts and manures are fantastic additions to your farm. They increase organic matter (OM), improve moisture holding capacity, help with nutrient cycling, promote microbial activity, and help to feed your soil. Organic amendments are, however, challenging to work with; they’re inherently variable, heavy to schlep around, and release nutrients over years which makes nutrient management planning difficult.

If you applied compost last year, or for the last 3 years in a row, it’s worth remembering that mineralization of nutrients from those applications is still occurring. Considering this whilst planning how much to apply in 2023 could save your back, your wallet, and prevent overloading your system with nutrients (most often phosphorous and salts). The specifics of each compost vary widely and temperature, source material, product maturity, etc. all effecting field conditions. Generally, solid organic amendments will release less than half of their nutrients the first year and the rest slowly over the next 5-10 years. It's easy to forget about the residual nutrients within your system!

 Fig 1. “Char application restores soil carbon and productivity”

There are only a couple of pieces of information you need to start understanding the nutrients within your organic matter applications: The source of your amendment (animal /plant/fungi as well as maturity), how much you apply per season, and how many years you have been applying it. With this information and a couple of excellent resources (linked below) you can develop a sustainable nutrient management plan that allows you to maintain or increase your soil OM levels without overloading your system.

How to interpret a compost analysis report

Nutrient Management Planning for Organic Systems

One last word on composts: don’t be afraid to mix things up. By changing the source of compost that you apply, you can help balance your system. For example, if you routinely apply animal-based composts, switch to mushroom, plant, or sea-based composts and vice-versa. There are some excellent local compost producers in Nova Scotia and your soil will perform better on a balanced diet.

Tim M


Fig 1: Char application restores soil carbon and productivity, American Society of Agronomy, https://www.eurekalert.org/news-releases/650195

How to interpret a compost analysis report: https://ofcaf.perennia.ca/wp-content/uploads/sites/19/2022/11/How-to-Interpret-a-Compost-Analysis-Report.pdf

Nutrient management Planning for Organic Systems: https://projects.sare.org/wp-content/uploads/1166nutrient-management.pdf