Fertilizing
I allocate about one acre of that old pasture to garden land. In any given year my shifting gardens occupy one-third of that acre. The other two-thirds are being regenerated in healing grass. I measure my garden in fractions of acres. Most city folks have little concept of an acre; its about 40,000 square feet, or a plot 200’ x 200’.
Give or take some, the plow pan of an acre weighs about two million pounds. The plow pan is that seven inches of topsoil that is flipped over by a moldboard plow, the seven inches where most biological activity occurs, where virtually all of the soil’s organic matter resides. Two million pounds equals one thousand tons of topsoil in the first seven inches of an acre.
Five percent of that one thousand tons can be organic matter, up to fifty priceless tons of life that changes 950 tons of dead dust into a fertile, productive acre. If 10 percent of that fifty tons is lost as a consequence of one year’s vegetable gardening, that amounts to five tons per acre per year lost or about 25 pounds lost per 100 square feet.
Patience, reader. There is a very blunt and soon to be a very obvious point to all of this arithmetic. Visualize this! Lime is spread at rates up to four tons per acre. Have you ever spread 1 T/A or 50 pounds of lime over a garden 33 x 33 feet? Mighty hard to accomplish! Even 200 pounds of lime would barely whiten the ground of a 1,000 square-foot garden.
It is even harder to spread a mere 5 tons of compost over an acre or only 25 pounds on a 100-square-foot bed. It seems as though nothing has been accomplished, most of the soil still shows, there is no _layer _of compost, only a thin scattering.
But for the purpose of maintaining humus content of vegetable ground at a healthy level, a thin scattering once a year is a gracious plenty. Even if I were starting with a totally depleted, dusty, absolutely humusless, ruined old farm field that had no organic matter whatsoever and I wanted to convert it to a healthy vegetable garden, I would only have to make a one-time amendment of 50 tons of ripe compost per acre or 2,500 pounds per 1,000 square feet.
Now 2,500 pounds of humus is a groaning, spring-sagging, long-bed pickup load of compost heaped up above the cab and dripping off the sides. Spread on a small garden, that’s enough to feel a sense of accomplishment about. Before I knew better I used to incorporate that much composted horse manure once or twice a year and when I did add a half-inch thick layer that’s about what I was applying.
Fertilizing Vegetables with Compost
Will a five ton per acre addition of compost provide enough nutrition to grow great vegetables? Unfortunately, the answer usually is no. In most gardens, in most climates, with most of what passes for “compost,” it probably won’t. That much compost might well grow decent wheat.
The factors involved in making this statement are numerous and too complex to fully analyze in a little book like this one. They include the intrinsic mineralization of the soil itself, the temperature of the soil during the growing season, and the high nutritional needs of the vegetables themselves.
In my experience, a few alluvial soils that get regular, small additions of organic matter can grow good vegetable crops without additional help. However, these sites are regularly flooded and replenished with highly mineralized rock particles. Additionally, they must become very warm during the growing season. But not all rock particles contain high levels of plant nutrients and not all soils get hot enough to rapidly break down soil particles.
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