Soil

Covering most of the land on earth, soil is an ecosystem of inorganic (rocks, minerals, air, water) and organic (dead and living organisms) substances that provide essential nutrients and structure to plant growth. The concept of the soil food web emphasizes the interdependence of participants in soil ecosystems.

Good Soil is Alive

The rocks, clay, and nonliving components of soil contain in abundance the raw materials to sustain plant life (nitrogen, potassium, phosphorous), but those nutrients aren’t available to plants in their raw forms. It takes living components like bacteria, fungi, protozoa, nematodes, and microarthropods to convert them into plant-available molecules (e.g. converting raw phosphorous into phosphates). These creatures also act as a buffer, reabsorbing excess nutrients plants don’t take up, and making them available later.

Likewise, plants need nitrogen (part of the chlorophyll molecule) in the form of nitrate (NO₃), which is produced by the same kinds of smaller life forms in soil from ammonium (NH₄⁺). This process (ammonium oxidation) is an aerobic reaction: it depends on available oxygen, so it cannot occur in waterlogged or compacted soil or if you don’t turn your compost pile often enough. Ammonium comes from decaying organic matter (manure, compost), or as a product of bacteria that convert atmospheric nitrogen (N₂) to ammonium.

Building Nutrients in Soil

Add decaying organic matter

• use fallen leaves for mulch and compost
• straw makes a good soft mulch as well, but it shouldn’t have grass seed in it that will sprout
• Build a hugelmound using dead wood and organic matter to return fertility to the soil. The result is a fertile hill that can act as a bed.
• Mulch around young trees to double the growth rate of trees under 10 years old. But don’t let the decomposing mulch touch the tree base to avoid rot.

Plant nitrogen-fixing plants nearby

Nitrogen-fixing plants cooperate with bacteria to turn atmospheric nitrogen into soil-available forms. While they use some of it themselves, they emit the remaining nitrogen into the soil. Legumes (peas & beans) are a common example of nitrogen-fixing plant, though there are many others.

Cover Your Soil

Covering bare soil (like in garden beds) prevents erosion, suppresses weeds, retains water and nutrients, and replenishes nutrients when covered in decaying organic matter. Leaves, compost, mulch, straw, dried-out manure, or parts of the plants themselves (chop-and-drop at the end of growing season) all serve this purpose. Covering beds over winter like this helps get them ready for spring planting.

From GrowVeg on YouTube

Dig a Compost Pit or Trench over Winter

Also from the above YouTube video, you can bury compostable material like kitchen scraps in the fall where you expect to have plants next spring, letting them compost over winter. Dig a hole where you expect to have a single plant (or trench where you’ll have a row of them), bury compostable material, and then cover it with soil to keep animals out and the heat in to sustain decomposition.

Further Reading

• How to Build Great Soil Masterclass, a 4-part video presentation by soil scientist Dr. Elaine Ingham, author of the USDA’s Soil Biology Primer.
• How to Cultivate Indigenous Microorganisms, a method for collecting microbes from wild soil and transplanting them to yours.
• The Soul of Soil, an ode to the substrate