How to check the quality of your compost tea
The best recipe is useless if you do not know what is in the tank at the end. In the first post, I described what is important when brewing. Today, I will show you how we check whether the compost tea delivers what it promises – using methods that you can largely apply yourself.
The cress test: simple, inexpensive, honest
Cress germinates within days and reacts sensitively to everything that is not right in the substrate. This is exactly what makes it the ideal test bench.
We test in four variants: open and closed, each with and without compost tea.
The closed variant is the strictest. Immature compost releases gases, and in a closed vessel, these gases inhibit germination immediately. Mature compost shows no difference to the open variant here.
The cress test therefore answers two questions at once: Is the compost mature? And does the tea promote root growth?
A trial at the Oeschberg Horticultural School shows that the method also works outside our farm: a prospective gardener tested our compost tea in a cress test with container substrate. The result matches our tests – significantly better root growth with compost tea. The active microorganisms stop harmful metabolic processes in the substrate and convert them into growth-promoting nutrients.
Under the microscope
What we want to see: fungal hyphae, protozoa, and testate amoebae. We are particularly interested in the protozoa – their excretions are excellent biostimulants. Where they are active, the nutrient cycle is running.
And a simple sign for which you do not need any specialist knowledge: movement. A living tea is teeming.
Bacteria: diversity is what matters
You will not be able to determine individual bacterial species with a light microscope. You don’t have to, either. We are interested in diversity: as many different shapes and sizes as possible.
The example of Brevundimonas shows what lies within this diversity. The genus lives aerobically, occurs in different soil types, and belongs to the “plant growth promoting rhizobacteria.” In a trial with potatoes, it increased yield and improved nitrogen uptake.
You only multiply such high performers if the tea remains consistently aerobic. That is why oxygen monitoring during brewing is part of the quality check for me. The EdaLife brewing systems with EDAPRO ingredients have been tested multiple times to ensure the oxygen content is always in the optimal range during the 24 hours. This makes measuring dissolved oxygen during compost tea production unnecessary.
Making humic substances visible
With circular chromatography, we make the diversity of humic substances in the compost visible. Under the microscope, you can recognize large humic acids as dark, amorphous clusters.
The image above comes from permanent grassland – that is where this diversity is at home. With compost tea, it can also be established on arable soils to promote humus formation.
What you don’t see can still be effective
Not everything shows up in the eyepiece. In our Petri dish tests, Trichoderma species regularly grow whose hyphae were not visible under the microscope. A microbiometer also detects fungi that you cannot find in the image.
If you want to know exactly
Microscopy can be learned – corresponding courses are available at Inforama, for example. And if you want to know what is actually living in your compost, your tea, or your soil, we can look at it together in an analysis – or you can get in touch for a personal consultation.
