Decay!

In an ecological system, the decay of organic matter, in all its forms, is the backbone of soil fertility

My past two articles have dealt with management techniques build soil fertility, break pest lifecycles, and adapt a perennial system to the effects of replant syndrome. The takeaway from both articles should be that a robust ecology leads to healthy pest and disease resistant plants. 

A common thread between those two articles is the primary focus of this one: decay! In an ecological system, the decay of organic matter, in all its forms, is the backbone of soil fertility. Unless you’re using only water-soluble fertilizers, it is through the decay of organic matter that fertilizer is made available to your crops. 

Decay, Fungi and Humus Development

Understanding soil mineralization — the release of mineral nutrients from organic matter — is key to building fertile, healthy soil that grows high yields of healthy crops and resilient ecosystems. 

Nature doesn’t run on synthetic fertilizer; it runs on carbon, cycling through life, death and decay. The growth and metabolism of decomposer organisms, the lifeblood of our soil, is fueled by organic matter. Maximizing photosynthesis on our fields increases carbon available to decomposer organisms. The decay of those carbon compounds results in the liberation of the essential plant nutrients for our crops. 

What it all comes down to is LIFE! The concept of a “living soil” is no trifle. Living organisms are essential for the functioning of each part of fertile soil. Through time (while succession occurs), we can decrease the use of imported biocides while simultaneously increasing life that creates fertility. 

There are myriads of life forms that we could discuss, but let’s focus on fungi. When wood falls to the ground, what decomposes the wood? Primarily fungi. When an old cherry orchard is cut down, what decomposes the old root systems? Primarily fungi. What decomposes last year’s crop residue and roots? Yep … primarily fungi.

Fungi derive their energy through saprophytic digestion. Here’s a brief summary of how that works. 

1. Fungi release enzymes into their environment, such as proteases, ligninases and cellulases. These dissolve complex organic compounds such as lignin and cellulose (the primary components of wood) and proteins that are found in dead plant or animal material. These enzymes are essential for the release of nutrients bound up in animal manure (which is merely organic matter that’s been pre-digested). Soy-based fertilizers, compost, alfalfa meal, gurry, slurry and kelp all require fungi to digest them in order to release nutrients to your crop.
   
2. The enzymes released by fungi break large, complex molecules into smaller pieces — mainly amino acids, fatty acids and simple sugars. 
   
3. Having first dissolved large molecules into small, the fungi then absorb these smaller molecules directly through their hyphae, the thread-like structures that are the actual body of the fungi. (A mushroom is merely the fruiting body of a fungus.) The absorption of these simple molecules provides the fungi with nitrogen, carbon and other elements it needs for growth and eventual reproduction. 
   
4. Fungi then use these nutrients in aerobic respiration (if oxygen is available) or fermentation (if oxygen is scarce). In aerobic respiration, glucose is broken down into ATP (adenosine triphosphate) through the Krebs cycle and electron transport chain, providing energy. In anaerobic conditions, fungi use fermentation to produce energy, yielding ethanol, methanol, organic acids (such as the acetic acid in vinegar glucuronic acid in kombucha), hydrogen sulfides and aldehydes. (These are not always what we want in our crop fields — thus the need for loose soils that keep the environment aerobic.) 

This breakdown of complex organic matter into simpler molecules, which are then reabsorbed into fungal bodies, is crucial for nutrient cycling. It is what re-separates nitrogen, phosphorus, potassium, calcium and other essential plant nutrients from the carbon to which it was attached, and it releases stored sunlight into the system as energy. If you kill your soil fungi with toxic chemistry, you will lose this essential source of fertility. 

“But won’t fungi attack and kill my crops?” Yes, there are fungi that will go to work digesting your crops! That is the job of SOME of them. Not all of them. A buildup of cherry-root-digesting fungi is one of the “causes” of orchard replant syndrome, for example. Cold, wet soil with a buildup of corn-digesting fungi will rot your seed corn. All true — but not an issue once you have an ecological understanding and work to build a balanced ecosystem. 

Categories of Fungi

There are two major categories of fungi: white rot and brown rot. These are the front-line of nature’s cleanup crew — the fungal first responders. White rot fungi and brown rot fungi each have a different job.

White Rot Fungi

White rot fungi go after lignin. Lignin is what makes wood tough. It’s the rock-hard glue that holds plant cell walls together. It gives a plant rigidity and stiffness. Lignin is the material that keeps corncobs and roots rolling around for years and years. Very few organisms can break it down. White rot fungi, though, releases enzymes such as peroxidases that tear lignin apart and leave behind mostly cellulose and hemicellulose. This is the process that turns hard, woody material into something soft and stringy — kind of like a punky log or wet, shredded paper.

The breakdown of lignin is what frees up the carbon, hydrogen and oxygen (carbo-hy-drates!) that were locked up in that dense structure. It also releases the nutrients (calcium, magnesium, zinc, boron, etc.) and makes them available to be cycled back into the ecosystem, aiding plant growth. Without white rot fungi, we’d be knee-deep in dead trees or straw that just wouldn’t rot. 

Brown Rot Fungi

Brown rot fungi take a different approach. Instead of going after lignin, they target cellulose and hemicellulose, leaving behind a crumbly, brown mass. These fungi use a process called a “Fenton reaction” that creates reactive oxygen that breaks apart wood fibers. This makes the wood crack and cube into a dry, brick-like form. It’s basically a controlled burn at the microscopic level. 

One of the special things about brown rot fungi is that they don’t completely decompose what they work upon. They leave it behind as a complex — a stable, fairly non-reactive organic material that is an early stage of humus formation. This leftover material becomes part of the soil. It adds structure, water holding capacity, and long-term carbon storage. It is literally a sponge and is able to hold water-soluble nutrients that your crops can easily access. 

Soil Fertility

Soil fertility is thus created through a two-step process:

Phase 1: Breakdown

1. Decomposition of organic matter: Leaves, plant residues, dead organisms, manure and other organic materials start decomposing, beginning with fungi, insects, grinders and chewers.
2. Partial breakdown (humification): With the help of brown rot and white rot fungi, the organic material is fully broken down into simpler compounds, such as carbon dioxide, water and nutrients. Some of the lignin is not quite decomposed at this time. 

Phase 2: Rebuilding 

Over time, the partially decomposed organic matter left behind by Phase 1 is re-mixed with soil minerals and microbial life. This is the process that creates humus — the dark, sponge-like material that holds water, stores carbon and slowly releases nutrients over decades. Humus is what gives rich, black soil its life-giving fertility. As you increase stable humus, you are increasing the cation exchange capacity of your soil. 

1. Mixing with soil minerals: The decomposed and partially decomposed organic matter interacts/reacts with minerals in the soil, mostly clay and silt, forming organo-mineral complexes that help stabilize the organic matter. This is where larger soil life such as earthworms come in handy, mixing and gluing organic matter and minerals together. 
2. Microbial transformation: Soil microbes further modify the remaining organic compounds and reassemble them into humic substances, which are more resistant to decay and have a long-lasting presence in the soil.
3. Formation of humus: The final product, humus, is a dark, stable, and nutrient-rich organic material that improves soil structure, water retention and fertility. All of this can happen completely naturally and free of charge when you farm ecologically. 

Chemical fertilizers give plants a quick fix, but they do nothing to build long-term soil fertility. Real, long-lasting fertility comes from a healthy, functional ecosystem: sunlight, water, and plant, animal and fungal life interacting with one another. Mycorrhizal fungi extend plant roots, bringing phosphorus and other nutrients to your crops. Brown rot and white rot fungi break apart lignin and cellulose to eventually form humus. Nitrogen-fixing bacteria pull free fertilizer straight from the air. Predator microbes keep disease organisms in check. 

How To

So, how do we actually do this? It’s a simple (but complex!) process that has been practiced by Acres U.S.A. readers for decades:

1. Balance your minerals. Provide your soil life with an abundant, balanced selection of minerals. If nothing else, correct the largest deficiency, and dedicate yourself to continual improvement. 
   
2. Include cover crops and perennials. Keep roots in the ground year-round to feed soil life and prevent erosion. Strive to optimize photosynthesis in order to feed the organisms that create fertile soil. Use tillage to disturb the system to release nutrients for the next crop phase. 
   
3. Feed your crops balanced, organically based fertilizers: composted animal manures, fish waste, plant meals, etc. 
   
4. Reduce, and aim to eliminate, toxic chemistry. Pesticides and fungicides don’t just kill pests; they kill the very organisms that create healthy, fertile soil and that keep plants healthy. Nature creates healthy, fertile soil following certain natural processes. Learn how to assist those natural processes and you will earn the right to eliminate toxic chemistry. 

So, next time you see a rotting log covered in mushrooms, don’t think of it as decay — think of it as the beginning of new life, a necessary step in nature’s grand design. We’re making soil. 

Mark Shepard is a land designer and consultant and is the author of Restoration Agriculture, Water for Any Farm and the Water for Any Farm Technical Manual.