Teeming with Microbes
An Organic Gardener’s Guide to the Food Soil Web
Article by Paul Gaylon
Inspired by the book “Teeming with Microbes”
by Jeff Lowenfels & Wayne Lewis
Rhizosphere: The region of soil surrounding plant roots where interactions between roots & soil environment occur; roots interact with microorganisms, bacteria, fungi, organic matter, nematodes, protozoa, worms, etc. Roots exudate carbohydrates (including sugar) and protein. All roots compete for water and minerals to absorb nutrients. Bacterium and fungi utilize exudates via ingestion. Nutrients from these interactions are absorbed and cycled back up the plant roots continuing the Soil Food Web. Plants can slow down or speed up this cycle.
The Soil Food Web provides nutrients for plants and breaks down food waste. Soil contains worms and other living organisms; soil products minerals and beneficial bacterium. Certain types of bacteria and fungi exude inhibitory compounds near the roots which protect plants from pathogenic bacterium and fungi. They also produce vitamins and antibiotics which enhance overall soil health.
Mycorrhizae are a special type of fungi that have a symbiotic relationship with plant roots. Nutrients are mineralized and cycled down. 90–95% of plants produce mycorrhizae which are quite beneficial. They increase root surface area and holding capacity; they also stimulate root growth, enhance nutrient and water uptake, are drought-tolerant, and help curb root shock. Mycorrhizae benefit the entire plant rooting area (Page 70).
Mycorrhizal fungi obtain the carbohydrates (energy) that they need from the host plant’s exudates. They use this energy to extend out into the soil; they pump moisture and mine nutrients from areas that plant roots cannot access. Water fills porous areas in the soil. Important bio-electrical connections are able to occur between roots and soil.
Bacteria have genetic material that is not enclosed by nuclei. They are simple sugars derived from plant roots and they help the soil to evolve and change. Bacteria release N2 from NH4 to fix plant nodes. Cyanobacteria are produced on Azolla ferns in rice paddies. As they die, their nutrients are passed along to plants. Algae leave a film that holds the soil and allows the plant to absorb 10x its weight in water. This protects plants from the effects of harsh conditions during droughts.
Fungi usually take up more complex nutrients including those that occur from cellulose breakdown. Fungi use plant exudates to bring food back to root tips. Chemicals secreted by fungi help provide minerals and nutrients from the soil; they free up nutrients and bring back phosphorous. Phosphorus helps with energy production (Page 130). Fungi add to the decay and utilization of algae. An example is the rice plant which gets N2 from water via algae. Good results have been seen throughout Asia. Fungi have had a symbiotic relationship with soil microbes and aquatic plants (algae) for 450 million years!
Hyphae are fungal strands that live and grow in soil. They attach to soil particles, deliver water and oxygen throughout the soil, and create tunnels while branching out.
Legumes enter plant roots through the root nodules. Plants provide bacteria along with oxygen, carbon, and protein as nutrients in addition to providing them with a place to live. Bacteria travel with exudates via hyphae.
Glomalins are glycoproteins that hold soil particles together. Complex interactions occur within the soil (& its PH) during the processes of decomposition and releasing of nutrients.
Good soil composition is composed of about 1/3 sand, 1/3 silt, and 1/4 clay. Organic matter makes up the rest of the composition. Nitrates (NO3) and chemicals harm soil. Ammonium (NH4) is more bioavailable in better soils.
The Soil Food Web approach is helpful with all aspects of plant growth including water retention, aeration, mineral breakdown, decomposition, soil texture, and nutrient production. Too much bacteria in the soil lead to a larger amount of NO3 which can cover crops and grasses. The number of bacteria in soil should be less than or equal to the number of fungi. Fungi help increase growth in trees, shrubs, perennials, grasses, and virgin forests exponentially! The number of fungi and bacteria present correlates to the length of time the tree or plant has had to establish itself. (from foodsoilweb.com)
Compost can contain wood chips, branches, leaves, and other woody and fibrous matter; compost supports fungi. Grass clippings, weeds, and kitchen scraps support bacteria. Tree and grass clippings in compost provide for a good balance; keep adjusting and turning the compost pile. One can always change ratios if necessary. Alfalfa meal (50 lbs.), grass clippings, and straw can also be composted together for good results. Mulching is also important as is making compost tea. Blue-Green Algae are excellent to use in compost tea. For vegetable plants, materials supporting bacterium should dominate. Chenopodioideae (Amaranth) & brassiere (cabbage family) use bacteria rather than mycorrhizal fungi. Composting increases the humus or humic acid content of the soil, and possibly fulvic acid in some cases. Soil retention & structure are enhanced by good, well-shredded nutrient-rich compost. This assures that soil erosion is mitigated and fine compost provides a healthy basis for the rhizosphere to provide great soil and healthier plants.