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Soil Care Basics: Increasing Organic Matter and Mineral Availability

Table of Contents

Introduction ManuresCompostsFertility PatchesCover Crops


Composting is the great recycler of almost any organic “wastes.” It reduces the bulk of organic materials, stabilizes their more volatile and soluble nutrients, and speeds up the formation of soil humus. A properly made compost heap is assembled by layering more readily decomposable materials (wet, green, fresh, high-nitrogen) such as manures, crop residues, kitchen wastes, weeds, and other fresh green plant materials such as pasture cuttings—with less decomposable materials (drier, coarser, denser, more high-carbon) such as autumn leaves, straw, and residues of harvesting such as corncobs. The carbon to nitrogen (C:N) ratio is important—say an average of about 30 parts carbon to one of nitrogen—for efficient decompositon by the microbes that feed on the composting materials and break them down into simpler, more stable compounds. Heat is generated by the process. A temperature of 110° to 130° F is probably optimal for the thermophilic (heat-loving) microbes driving the decomposition, but such temperatures help kill weed seeds and disease organisms. Since water and oxygen are essential to the microbes, the pile should be moistened as it is assembled, but should not be sopping wet, which would decrease availability of oxygen and encourage growth of pathogenic organisms. The pile must be large enough to retain much of the heat of decompositon, but not so large that oxygen cannot penetrate to the center. Aeration is encouraged by mixing in the coarser elements throughout, ensuring plenty of air spaces. After the heat peaks, the heap should be turned—with the outer layers going to the inside and vice versa—to incorporate more oxygen and generate a new heating cycle. A third turning is sometimes necessary to complete the process.

Composting is at least as much art as science. More than anything I know, it is something to “learn by doing.”

Composts are great for improving soil quality and water retention, disease suppression, and humus content (though less decomposed materials such as manures and green plants give a more immediate “flush” of nutrients when applied directly). However, they are quite labor-intensive. The older I get, the more interested I am in an easier alternative. Fortunately, there are three.

In classic composting, we layer the more high-nitrogen, easily decomposed elements with the high-carbon, difficult to break down materials. Suppose instead we keep these two types of compost materials separate, and simply apply them in two layers directly to the garden bed. This is the concept of “layer composting” or “sheet mulching&rdquo—it has even been called “lasagna gardening.” The more moist, volatile, high-nitrogen materials go down first, in direct contact with the soil and the microbial populations ready to feed on them, while the drier, coarser, high-carbon elements are used as a cover to keep the first layer from drying out or losing its more volatile elements to the atmosphere.



An effective—and fun—alternative to labor-intensive classic composting is vermicomposting, using earthworms to convert nutrient-dense materials such as manures, food wastes, green crop residues, etc. into forms usable by plants. You can buy manufactured worm bins in which the worms grow and convert what you feed them, or you can easily make your own. You can also buy composting earthworms. Note that the species used is usually Eisenia foetida or related species—“red wrigglers” or “manure worms” (the sort you will find in an aging manure pile, which indeed you could use to “seed” a population in your bin), rather than species that burrow deep into soil like “night crawlers.” I started out with a 3x4-ft worm bin, then last year converted the center of my greenhouse to a 4x40-ft series of bins, 16 inches deep. My worms process horse manure by the pick-up load from a neighbor who breeds and boards horses, and the earthworm castings are a major part of our fertility program. Not only do castings help feed plant roots, they carry a huge load of beneficial microbes that boost the soil organism community.


Chicken Power!

Another fun alternative to composting is chicken power. I use electric net fencing to manage my chickens, rotating them from place to place on pasture. When needed, however, I “park” them on one of my garden spaces, onto which I have simply dumped whatever organic materials I would once have used to assemble compost heaps. The chickens happily do what they love best—scratch ceaselessly through that material looking for interesting things to eat, in the process shredding it and incorporating it into the top couple inches of soil, the zone of most intense biological activity. Their droppings, scratched in as well, give a big boost to the soil microbes.