A simple, practical rhizosphere test is to pull a plant or two and look at the roots. Is the soil clinging to the roots? If it is, you have plants that are producing root exudates for the soil microbes and soil microbes that are exchanging nutrients with the plant roots. If you don’t your plants are not in communication with the soil microbiome.
There are fungi, bacteria, archaea, protozoa, algae, yeast. They aggregate the soil into clumps, leaving pore space for air and water. They are a dynamic being, changing quickly with the environment. They communicate, not through words but through a type of species-unique chemical called an autoinducer. Over longer distances the mycorrhizal fungi can carry water, carbon and other plant nutrients.
Plants exude long chains of carbon through their roots. Microbes form these carbon chains into aromatic rings which are an integral part of humus. Humus is a wonderful support for plants; it holds water, nutrients, helps to chelate minerals to make them plant available, provide soil structure and porosity. Microbes don’t need humus directly, but they do need plants. Plants are less stressed when there is humus around. It’s a symbiotic relationship.
There are those who says that decomposition (composting for example) ultimately results in the decomposed carbon being released into the atmosphere. They say it takes living plants and microbes to produce humus and build soil carbon. Fungal decomposition doesn’t build humus. Living plants in communication with the microbiome builds humus.
Conventional wisdom has it that brassicas (plants in the cabbage family) don’t form mycorrhizal associations. The glue that holds the soil onto the roots of the plant is glomalin, a sticky substance produced by arbuscular mycorrhizal fungi, the very ones that should not be associating with our kale roots. But there it is, soil stuck to the kale roots, go figure.
The kale in the picture had a pretty heathy rhizosphere before it was tugged out of the ground. The soil has been amended and balanced acording to OrganiCalc.
It is an amazing world underground! It’s well worth it to be a bit curious and see what’s down there.