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.
Soil temperature has a great deal to do with how effectively compost
can act as fertilizer. Sandy soils warm up much faster in spring and
sand allows for a much freer movement of air, so humus decomposes
much more rapidly in sand. Perhaps a sunny, sandy garden on a
south-facing slope might grow pretty well with small amounts of
strong compost. As a practical matter, if most people spread even
the most potent compost over their gardens at only twenty-five
pounds per 100 square feet, they would almost certainly be
disappointed.
Well then, if five tons of quality compost to the acre isn't
adequate for most vegetables, what about using ten or twenty tons of
the best. Will that grow a good garden? Again, the answer must allow
for a lot of factors but is generally more positive. If the compost
has a low C/N and that compost, or the soil itself, isn't grossly
deficient in some essential nutrient, and if the soil has a coarse,
airy texture that promotes decomposition, then somewhat heavier
applications will grow a good-looking garden that yields a lot of
food.
However, one question that is rarely asked and even more rarely
answered satisfactorily in the holistic farming and gardening lore
is: Precisely how much organic matter or humus is needed to maximize
plant health and the nutritional qualities of the food we're
growing? An almost equally important corollary of this is: Can there
be too much organic matter?
This second question is not of practical consequence for biological
grain/livestock farmers because it is almost financially impossible
to raise organic matter levels on farm soils to extraordinary
amounts. Large-scale holistic farmers must grow their own humus on
their own farm. Their focus cannot be on buying and bringing in
large quantities of organic matter; it must be on conserving and
maximizing the value of the organic matter they produce themselves.
Where you do hear of an organic farmer (not vegetable grower but
cereal/livestock farmer) building extraordinary fertility by
spreading large quantities of compost, remember that this farmer
must be located near an inexpensive source of quality material. If
all the farmers wanted to do the same there would not be enough to
go around at an economic price unless, perhaps, the entire country
became a "closed system" like China. We would have to compost every
bit of human excrement and organic matter and there still wouldn't
be enough to meet the demand. Even if we became as efficient as
China, keep in mind the degraded state of China's upland soils and
the rapid desertification going on in their semi-arid west. China is
robbing Peter to pay Paul and may not have a truly sustainable
agriculture either.
I've frequently encountered a view among devotees of the organic
gardening movement that if a little organic matter is a good thing,
then more must be better and even more better still. In Organic
Gardening magazine and Rodale garden books we read eulogies to soils
that are so high in humus and so laced with earthworms that one can
easily shove their arm into the soft earth elbow deep but must yank
it out fast before all the hairs have been chewed off by worms,
where one must jump away after planting corn seeds lest the stalk
poke you in the eye, where the pumpkins average over 100 pounds
each, where a single trellised tomato vine covers the entire south
side of a house and yields bushels. All due to compost.
I call believers of the organic faith capital "O" organic gardeners.
These folks almost inevitably have a pickup truck used to gather in
their neighborhood's leaves and grass clippings on trash day and to
haul home loads from local stables and chicken ranches. Their large
yards are ringed with compost bins and their annual spreadings of
compost are measured in multiples of inches. I was one once, myself.
There are two vital and slightly disrespectful questions that should
be asked about this extreme of gardening practice. Is this much
humus the only way to grow big, high-yielding organic vegetable
gardens and two, are vegetables raised on soils super-high in humus
maximally nutritious. If the answer to the first question is no,
then a person might avoid a lot of work by raising the nutrient
level of their soil in some other manner acceptable to the organic
gardener. If the answer to the second question is less nutritious,
then serious gardeners and homesteaders who are making home-grown
produce into a significant portion of their annual caloric intake
had better reconsider their health assumptions. A lot of organic
gardeners cherish ideas similar to the character Woody Allen played
in his movie, Sleeper.
Do you recall that movie? It is about a contemporary American who,
coming unexpectedly close to death, is frozen and then reanimated
and healed 200 years in the future. However, our hero did not expect
to die or be frozen when he became ill and upon awakening believes
the explanation given to him is a put on and that his friends are
conspiring to make him into a fool. The irritated doctor in charge
tells Woody to snap out of it and be prepared to start a new life.
This is no joke, says the doctor, all of Woody's friends are long
since dead. Woody's response is a classic line that earns me a few
chuckles from the audience every time I lecture: 'all my friends
can't be dead! I owned a health food store and we all ate brown
rice.'