A key indicator of your garden soil’s vitality is its teeming life. Gardeners love discovering earthworms in the soil, as these creatures serve many purposes. 

From a chemical standpoint, their excrement (worm castings) is nutrient-rich and easily absorbable by plants. On a physical level, they create conduits into the soil, facilitating the passage of air and water to plant roots. 

Biologically, earthworms feed on bacteria and other microbes in the garden. Each living organism within the soil plays a role in enhancing its health, collectively forming the “soil food web.” Ideally, we should be able to effortlessly dig into the soil with our hands and pull up signs of life big and small—all of which contribute to the soil and our crops.

Plants release exudates, or plant sugars, from their roots, which feeds microbial life in the soil. The diversity of crops planted contributes to a varied release of exudates, nourishing a diverse population of bacteria. These bacteria aren’t very mobile and cling to the plant’s roots. This is why, following a frost, we cut plants at the soil level and leave the roots in the ground. The microbes go dormant and thrive next season. 

In addition to bacteria, fungi play a crucial role by feeding on plant exudates and growing a network of fibers known as mycelium. Mycelium spreads outward, seeking water and nutrients to benefit the plants. The symbiotic relationship between fungi and plants is evident, as the fungi thrive when the plants remain healthy, producing plant sugars that support the underground fungal growth. In essence, while plants are fixed in one location, mycelium can extend up to 30 feet, actively acquiring and transporting nutrients back to the plant, thereby enhancing its capacity to absorb essential nutrients.

The intricate web extends beyond bacteria and fungi to include other essential microbes like actinomycetes and cyanobacteria. These microbes decompose existing organic matter and break down complex organic compounds into simpler molecules, making it easier for plants to absorb.

Next in the soil food web is protozoa, nematodes and small insects. These organisms play a dual role in the ecosystem by contributing to the decomposition process by shredding plant debris and effectively creating plant food. They also help control bacterial populations by consuming them. Interestingly enough, when these soil critters reach the end of their life cycle, their decomposing bodies make great plant food.

In the final tiers of the food web, larger insects such as pill bugs, centipedes and spiders feed on the decomposers to keep their populations in check. Earthworms fall into this group, but actively participate only when microbes are present in the soil.

Larger animals like rodents and birds feed on these insects and their byproducts, including manure, feathers and dead bodies. In doing so, they contribute an even greater diversity of nutrients to the soil and spread the microbes around as they move to different areas.

CARING FOR MICROBES

These rules are fundamental for maintaining a healthy and productive soil environment. 

Rule #1: All beneficial soil microorganisms need air to exist. The key to ensuring their survival is porous soil that isn’t compacted to allow for proper airflow. Envision healthy soil as forming sturdy dirt clods, as opposed to over-tilled clay flour, which turns into dust and hardens like cement when wetted down. Additionally, excessive rototilling grinds up earthworms and their holes and devastates mycelium networks.

Rule #2: Sustain microbial life with organic matter. Ideally, soil should contain around 5% organic matter, yet high desert soils typically register around 1%. Various materials, such as plant leaves, corn husks, carrot tops, compost, manure and straw mulch, are examples of organic matter that nourishes carbon-loving microorganisms. 

Soil microbes also play a crucial role in disease and pest management. The primary objective of these microbes is to maintain the vitality and health of the plant host, ensuring the continuous production of exudates.

Ongoing research in the field of biopesticides is of paramount importance as growers worldwide actively seek non-chemical alternatives to safeguard their crops from predators. Bacillus thuringiensis stands out for producing a toxin effective against soil grubs, while Bacillus subtilis serves as a natural antagonist to fungal pathogens. 

Send your gardening questions to Bryan in care of the BEACON, or email him at [email protected]

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