Composting: Science and Art

We are continuing with Farmer Al’s talk entitled “Compost: the new rage in sustainability” and using the slides from the talk to illustrate some of the weekly activities at Frog Hollow Farm as they relate to on-site composting and to compost tea application.

In the next few blogs, we will focus on how we decide that a compost windrow (pile) is ready for spreading in the orchard and how we go about preparing a compost tea.

Let’s start by listing the methods used to determine if compost is ready to be spread:

  • Temperature of the windrow is less than 110 F
  • Windrow has been turned a minimum of 5 times
  • At each turning of the windrow, the temperature was 130 (160 F maximum)
  • Microscopic analysis shows that bacteria, fungi, protozoa and nematodes are present in sufficient numbers
  • Microscopic analysis and respiration tests (CO2 evolution) show that  only a small percentage of microbes are active
  • The windrow passes an odor test: it has an earthy aerobic smell

These indicators of compost readiness are based upon a solid base of scientific investigation. However, starting materials that are used to start a compost windrow are not always exactly the same (in terms of microbial diversity). Also, at the end of a composting cycle, a small subset of microbes may react to a physical stimulus in a way that causes problems.

For the first time at Frog Hollow, we had to stop spreading a compost that had fulfilled all of the indicators listed except that at the last moment it developed an odor that was abnormal (anaerobic). The windrows are analyzed for their readiness while they in their usual trapezoidal shape (4 feet high and ~200 feet long), which is the best shape for air exchanges, turning , watering etc… After all the analyses were done, this windrow was pushed into a tall volcanic pile (~ 6 feet high) for storage purposes. It appears that this caused compaction and lead to conditions that stimulated anaerobic bacteria to reproduce  and cause odor problems. We decided that the fastest way to replace the anaerobic microbes with aerobic ones would be to water the pile with an aerobic compost tea. As soon as the odor of the pile reverts to an “earthy” smell, we will test it again before spreading it in the orchard.


To conclude: what is good compost? That is a topic for another blog.

Author: Christophe Kreis MLF Soil Consulting PhD, Molecular Biology/Developmental Biology, University of British Columbia, Canada. Christophe is co-founder of MLF Soil Consulting with his wife Monique. He started his career in basic medical research and after various positions in academia and industry Christophe slowly returned to his first passion Soil Ecology and Microbiology. It is his belief that human health is tied intimately to soil health through the production of healthy food. For this reason MLF Soil Consulting is committed to help farmers improve the management of their soil through composting, vermicomposting and biological analysis of microbial soil life.
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