The Soil Food Web

Graphical illustration of the web of interactions between microbes, plants, soil and animals

The Living Soil
by Tad Hussey

I get asked all the time about the importance of soil. Why is your growing medium so important? Many problems such as disease, poor yield, and unhealthy plants can be corrected by fixing the soil in your garden or starting with a good soil mix. Let’s dig a little deeper at what makes good soil so special….the biology.

Did you know that in one teaspoon of living soil there are 100 million to 1 billion bacteria,1 to 40 miles of fungal hyphae, and 1,000-100,000 protozoa? These organisms play an important role in plant health and growth. The bacteria eat the exudates (simple sugars, carbons, carbohydrates) that the plant puts out through its roots, which are then eaten by the protozoa. What is excreted by the protozoa is now plant-available nutrients. Beneficial fungi protect the plant from pathogens and harmful microbes, as well as creating pathways in the soil that bring water and nutrients back to the plant from larger distances. Bacteria and fungi work together in decomposing organic material and making the nutrients plant-available. This is a sustainable process known as “nutrient cycling” that allows for the growth of healthy plants, without the need for fertilizers, pesticides, and other chemicals. After all, there’s no one out there putting Miracle Gro on our rainforests, yet look at how successful plants are at growing in these microbial-rich environments.

So what went wrong? Why can’t the plants in your backyard grow in the same manner? The answer is simple. The biology necessary to cycle nutrients to the plant and protect it are no longer present or not present in adequate numbers. Where did they go? Well, they were killed off by chemical fertilizers, pesticides, fungicides, over-tilling, and compaction.

Chemical fertilizers and other ~cides contain salts. Remember back to high school science where you learned about the process of osmosis? It’s the movement of water through a cell membrane from a solution of low solute concentration to a solution with high solute concentration. In living soil, water is locked up in the cells of the microorganisms. With the proper biology in place, you can cut back on your watering by up to 30%! When salts in the form of chemical inputs are added to the soil, the water is drawn out of the microbes and they are either killed or go into a dormant state. Now the plant is dependent on you to provide all of its food and protection. That’s why you have to fertilize on a regular basis.

In addition to damaging the biology in the soils, these chemicals are having other impacts of much greater consequence. Nitrates from fertilizers are leaching into our water system, and pesticide exposure has been linked to a variety of serious diseases such as cancer. There’s a reason that lawn companies recommend keeping children and pets off lawns after they’ve been sprayed. These chemicals are highly toxic!

So what’s an alternative? This is a shift from our current N-P-K paradigm towards an organic way of gardening by feeding the microbes in the soil and letting them do the work for us. Our ancient ancestors gardened in this manner long before we knew what bacteria was! Fertilizer was in the form of manures, which was decomposed by the microbes and provided all the nutrients the plant needed. Recent studies have also shown that nutrition levels in plants grown organically are higher than those grown with conventional chemicals.

Using present day technology, we are now able to add these beneficial organisms back into our soils and feed them through a variety of organic inputs. The three best things you can do for your soil is to top dress with compost, mulches, and compost tea. Since many of you probably already know about the benefits of compost and mulch, I’d like to focus a bit more on compost tea.

When I say compost tea, I’m referring to actively aerated compost tea or AACT for short. This distinction is important because there is a big difference between throwing some compost or manure in a bucket and letting it sit for a couple of weeks and AACT.

AACT is an aerobic water solution that has extracted the microbe population from compost along with its nutrients. The concept behind compost tea is quite simple, though the actual process becomes scientific and has many variables that need to be accounted for. The idea is that compost (full of beneficial microorganisms), is put into water and then nutrients or foods for the microorganisms are added to allow the bacteria and protozoa to multiply rapidly and the fungi to grow. Air is sent through the water to keep the dissolved oxygen levels above 6 mg/liter, as this selects for the aerobic microorganisms, which are the ones found to be most beneficial. At the end of the brewing cycle, what you have is a concentrated liquid literally teeming with billions of microorganisms that can be sprayed directly onto the leaf surface of your plants on onto your soil. This puts the “good” biology where the plant needs it to protect itself. It keeps the plant healthier and helps to fight off potential diseases. The “good” biology occupies the infection sites on the leaf surface and survives by consuming the exudates that the plant puts out. The “good” biology, then out-competes the pathogens for the space on the leaf surface or around the roots (rhizosphere). This is how plants protect themselves and thrive in nature.

It is possible to make bad AACT. If you don’t start with good compost, don’t add the proper amount of nutrients, or keep the brew sufficiently aerated, you could be selecting for pathogens rather than beneficial microbes and end up with a tea that will have little to no effect on your plant or possibly even do damage.

Along with compost tea it’s important to do applications of other bio-amendments such as soluble seaweed, humic acids, and fish hydrolysate for example. Seaweed serves as a bacterial food substrate and also provides additional benefits for your plants in the form of growth hormones, increased stress resistance, and faster plant response. Humic acids serve as a fungal food, and also chelate (bond with) minerals in your soil and make them available to your plant (many minerals in your soils are “locked up” or unavailable to your plant). These sorts of applications work by feeding the microbes which in turn feed your plant.

When gardening in this manner, it’s important to adjust your application rates or program to fit within the needs of your garden. I’d suggest an initial topdressing of your garden with compost and an application of compost tea, adding soluble seaweed and humic acids to the tea after brewing. Then, another application 2-3 weeks before planting and another one when you plant your starters (adding mycorrhizal fungi into the hole at this time). In the fall, I’d add a mulch to your garden, followed by an application of compost tea (to speed up decomposition over the winter). You may or may not need an organic fertilizer (NPK below 10-10-10) to supplement the rest of your program.

Once an organic program has been established, typical application rates of AACT, humic acids, and seaweed are only 3-5 times per year. Now the plant is in charge, and the organisms are in place to cycle the nutrients for the plant. This is what sustainable gardening is all about!

In this manner, you can improve your soil, protect our water supply and environment, and grow healthy plants without chemical inputs. If you have any questions or want to learn more about this subject, go to www.gardeningwithmicrobes.com, or pick up a copy of Jeff Lowenfels book, “Teaming with Microbes.”