What is Good Compost?

By John Wallace, SIFT Farm Manager

Compost made on the SIFT farm.
Compost made on the SIFT farm. Photo: NCAT

Not all compost is created equally. Just because something can be decomposed does not make it the best amendment for your soil. A high-quality compost is full of microorganisms, while a low-quality compost is what I would call sterile dirt. You can think of all these microorganisms as a probiotic, just as you would yogurt. When used as a soil amendment, compost helps inoculate the soil with symbiotic microorganisms. These microorganisms actually unlock nutrients that were already in the soil that may have not been bio-available before. It is common practice to balance your compost with “greens,” which are high in nitrogen, and “browns,” which are high in carbon. The overall balance for making a good garden compost heap is considered by many to be around 30 carbons for 1 nitrogen. As you turn a compost heap, you disturb the fungi, which can lead to more bacterial dominated compost. However, there has been research into methods that can create a compost that is heavily dominated by fungi.

Three-bay composting system in progress.
Three-bay composting system in progress.
Photo: NCAT

Even though not all compost is created equally, there are still uses for the full range. For instance, a sterile dirt might not do much for your garden plot, but it is used regularly in our area for capping toxic mine waste, constructing foundations, and landscaping. One step away from sterile dirt are industrially treated compost mixes. Locally, a product by the name of Glacier Gold is available, which is a mix of topsoil and a compost made from the byproduct of sewage waste, known as bio-sludge, and organic material diverted from the landfill. I would never recommend using a product made from bio-sludge in your garden or farm; however, by the time it is treated, there is no risk of parasites or other health concerns. The truth is that, by its final stage, it likely has no probiotic qualities to benefit your garden. If anything, it is impressive that a valuable product can be made from otherwise wasted resources and might be fit for your landscaping needs.

Dr. David Johnson, Adjunct Professor for the College of Agriculture at Chico State and Faculty Affiliate for the Center for Regenerative Agriculture, is investigating the use of biological soil enhancements and their effect on carbon sequestration for the Institute of Sustainable Agricultural Research at New Mexico State University. In particular, he found that the ratio between fungi and bacteria in the soil is critical to a plant’s productivity in healthy agricultural systems and thus to a plant’s efficiency in nutrient uptake. It also increases the rate of carbon sequestration significantly. Dr. Johnson and his co-workers found that by increasing the ratio of fungi to bacteria to 5:1, compost application as low as 400 pounds per acre might be sufficient. If found suitable for rangelands, it would provide a more economical approach to rangeland restoration and soil carbon sequestration. They call their approach BEAM for “Biologically Enhanced Agriculture Management.”

Dr. Johnson and his wife, Hui-Chun Su, created a bioreactor for producing the fungal-rich compost. This device is able to cook down compostable material without turning and disturbing the fungi. Essentially, it is a breathable pillar filled with alternating layers of carbon- and nitrogen-rich materials. Straw or leaves would be considered carbon-rich, and then a manure could be used as a nitrogen-rich layer. Perforated pipes run down through the compost pillar, allowing water and oxygen to move through. This process takes up to a year to complete and depending on your winters, could take even longer. The result is a compost that looks a little different, more like a clay than a mulch. This final compost is more biologically diverse and nutrient-rich. It can greatly improve the biology and nutrient availability of the soil, improve water-retention capacity, and increase soil carbon sequestration, while greatly improving crop yields.

Posted on: October 14th, 2019