Saturday, August 8, 2009

Building and Feeding Healthy Soil, Part 3

How much and how often is it necessary to feed soil organisms?

The answer is like the answer to the question “how much does it cost to grocery shop”? It depends. “How many people are you feeding? Are you buying ground beef or filet mignon?” As soil organisms become active in greater numbers, they will eat more. Two inches of mulch may stay on top of poor soils for a year or more, but in healthy soils it sure won’t. The more the soil organisms eat of the right stuff, the larger and healthier the plants will grow and fruit.

I find that each year is different in what I need to add, and when. I continually add green manure all growing season. Since my beds are mostly raised rows, I constantly put all trimmed plant material and plants that have finished for the season directly on the paths, and cover with a layer of dirt. By the end of the summer, it has been nearly all broken down by the microbes.

In Part One, I said most soil organisms eat things containing carbon. In what is known as the carbon cycle, plants absorb carbon dioxide from the atmosphere and use it, combined with water they get from the soil, in the symbiotic process with the soil organisms to make substances they need for growth. The process of photosynthesis incorporates the carbon atoms from carbon dioxide into sugars that feed the soil organisms, although the plants themselves use some of it in the complexity of protein production.

Animals (I’ll use chicken here as an example) and humans eat the plants (such as cracked corn and greens the chickens eat), and use the carbon to build their own tissues. Animals, such as a fox (or humans), eat the chicken and then use the carbon for their own body needs. Animals (and humans) that have eaten the chicken and its carbon, now return carbon dioxide into the air when they (we) breathe, and also when they die, since the carbon is returned to the soil during decomposition (except in societies who entomb their dead in sealed compartments).

The carbon atoms in soil may then be used in a new plant, or by small microorganisms, and the carbon dioxide exhaled by animals gets recycled by new plants absorbing it for photosynthesis.

I jump-start the carbon cycle in a new garden area by adding biochar to my soil. Biochar is simply small bits of charred (not burned) plant material, including mature plant parts like firewood, and is often “inoculated” with some food source for the soil organisms. Fresh human urine works well as an inoculant. It is sterile, and contains 2-5% organic nitrogen, which doesn’t burn plants like commercial urea (man-made/chemical nitrogen) containing 45% nitrogen, found in farm/garden supply stores. Think of biochar as fully-equipped condos for the microbes.

You can also use a compost tea with some added molasses to inoculate biochar. The biochar I use is bits of charred wood left in the ashes of my wood stove. I sift them from the ash, and pulverize the bigger pieces into pea-size bits before inoculating than and incorporating them into my garden soil.

Biochar is a lengthy topic all by itself, and I will write a more detailed separate post on biochar soon. However, let me mention here not to use left-over bits of charcoal briquettes like those used for cookouts. They contain some nasty additives that are not good for the soil organisms.

Stay tuned for Part Four

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