Decay!

Ecological farmers need to know how to work with nature’s decomposition processes

In last month’s article, we introduced the process of pedogenesis, the process by which the Nature Operating System (Nature OS) creates soil. Now that it is early in the growing season on most North American farms and ranches, many of us are involved in cleaning the winter bedding pack out of sheds and barns. Some of us will directly apply cleanings to the soil, while others will be making and turning compost. A tremendous amount of compost is being applied this time of year all across the continent, and organic mulches are being spread. 

In many ecological writings (Charles Walters’ Eco-Farm and Gary Zimmer’s The Biological Farmer are two that come to mind) the chapter that follows soil creation usually photosynthesis. Yes, photosynthesis is the driver of ecological agriculture, but decomposition is one of the foundations of eco-ag. In nature, growth rates and the health and yield of plants are directly regulated by the rate at which nutrients are cycled and recycled within the decomposition process.

In early succession (as described last month), lichens and mosses get most of their nutrients directly from the processes of weathering, biological nitrogen fixation and deposition from the atmosphere. As succession continues beyond this stage, an increasing proportion of plant nutrients are recycled from the remains of previously living things. Large organic molecules in the lichens and moss (“organic” as in stuff that is or once was alive) are oxidized, releasing carbon dioxide, water, energy and decomposer organisms. Essential nutrients (nitrogen, phosphorus and sulfur) are released. New compounds are synthesized by the soil life, and some are protected from further decay. Aside from when disturbances (such as tillage) result in nutrient losses (oxidation, leaching, erosion, etc.), there is an overall trend toward nutrient cycling via the decay process as the main source of plant nutrients. “Manage your decay cycle!” I can still hear Gary Zimmer squealing at 300 mph. 

In an ecosystem, even in the simplified ecosystem of a crop field or pasture, the feedstocks for your soil’s decay cycle come primarily from the following sources: 

• Aboveground plant tissues, along with associated microbes and epiphytes
• Aboveground animals, large and small
• Belowground plant tissues and associated organisms, including roots, mycorrhizae, fungal hyphae and bacteria
• Detritus, which is any organic matter that is not contained within a living cell, humus or organic/mineral complex. There are three distinct forms that this dead organic matter takes: litter, dissolved organic matter and exudates. Simply put, litter is the leaves, stems and branches of plants; the dead bodies of organisms large and small; and feces. Dissolved organic matter is soluble carbon compounds leached from both living and decaying plant matter, and exudates are organic compounds released into the soil by roots, mycorrhizae and microbes. There is a wide variety of compounds exuded from living cells, including sugars, acids and enzymes. Litter releases its nutrients more slowly; root exudates can release them more quickly. Some dissolved organic matter can break down quickly and some quite slowly. 
• Humus and organo-mineral complexes are relatively stable in the scheme of things and are produced by the recombination of elements in the soil, mostly by the activity of microbes. The release of nutrients and energy from humus can take anywhere from years to decades. 
• Underground grazers and decomposer organisms themselves
• Throughfall from water running down plant stems and dripping off leaves after it has taken up dust particles, leaves and stem exudates
• Char. Char is the product remaining from the combustion of organic materials. As with anything in the natural world, it can be quite varied. Char from animal remains is different from plant char. Grass char is different than wood char. Char resulting from an oxygen-rich burn is different than char produced with limited oxygen. Char is not the same thing as biochar, as used in agriculture. Optimal biochar is the product of oxygen-limited combustion with temperatures in the 900 to 1,300ºF degree range. If combustion temperatures are above 1,300ºF, the char can become hydrophobic and its water and nutrient holding capacity can be greatly reduced. Pine char is different than oak char. Categorically, all char raises soil pH, which can be extremely beneficial to plants in acidic soils, but not so in already alkaline soils. 

That may seem like a lot of information to digest, but that’s OK. Ecological farmers don’t claim to know everything, and there is quite a lot that we don’t understand. When it comes to the Earth’s digestion process (decomposition), we don’t need to know how it all works. We just have to know how to work WITH it. 

Anyone who has planted a crop into a field that was corn the year before is all too familiar with the fact that certain things decay more rapidly than others. The leaves are almost all gone, stalks (if not baled and removed) remain as partially decomposed chunks, and sometimes roots and cobs can persist for years. Knowing the relative “digestibility” of your organic matter is an incredibly useful crop rotation and fertility management tool. It also can help you to gage the “appetite” of your decomposer organisms. Soil that is newly transitioned away from chemical agriculture will experience slower decomposition than a soil that has been ecologically managed for a number of years. Some mature agroforestry systems have such a well-developed decay cycle that they can digest one-inch-diameter hard, woody branches in a single season. 

Knowing this can help you understand cover cropping better, as well as compost, compost teas, and other biological products. Molasses (sugar) is a great, quickly available energy boost to kick-start your “herd” of decomposers. This will give a young, rapidly growing crop, or a crop in newly transitioned soils, a quick energy boost that will stimulate your crop to produce more root exudates, which begins the virtuous cycle. Compost teas are loaded with decomposer microbes and are like adding yeast to bread dough. A six-inch-tall green rye crop disked into the soil in preparation for seeding a main crop will have a lot of soluble carbon compounds, which are readily available as nutrients for a main crop. 

This easy-to-digest material doesn’t really create much long-lasting humus. The same rye grown to maturity, with the straw and stubble allowed to lay as a surface mulch, will decompose more slowly and feed different organisms. Vermicompost is not the same as a hot compost. Compost made from winter bedding is not the same as compost made from vegetable scraps or old hay. Wood chips made from small-diameter, living branches is high in soluble carbon compounds and will give you a quick flush of nutrients as they are leached out of the slow-to-decompose lignin matrix (you get quick release AND slow release). Dead wood requires so many decomposer organisms to break it down that it will take nitrogen right out of the soil solution, potentially starving a nitrogen-hungry crop — but it creates a fungi-rich humus. 

Each different source of the carbon in our system is another fertility amendment that we can grow on the farm. Knowing the relative decomposition rates of the carbon feedstocks gives eco-farmers a powerful planning tool. Each decomposition feedstock behaves differently, and each is perfect for its particular application. Get to know how they behave! 

I’m not merely piling soiled bedding in a cold spring day. I’m personally participating in the amazing and oftentimes mysterious process of turning manure into black gold! 

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.