infiltrate and roots to develop properly. Erosion contin-
would cut down and burn the trees in the new patch,
ues, and nutrients decline to levels too low for good crop
allowing the forest and soil to regenerate in previously
growth. The development of saline (too salty) soils under
cropped areas.
irrigation in arid regions is another cause of reduced soil
The westward push of U.S. agriculture was stimu-
health. (Salts added in the irrigation water need to be
lated by rapid soil degradation in the East, originally a
leached beneath the root zone to avoid the problem.)
zone of temperate forest. Under the conditions of the
Historically, soil degradation caused significant
humid portion of the Great Plains (moderate rainfall
harm to many early civilizations, including the drastic
and temperature, with organic matter distributed deeper
loss of productivity resulting from soil erosion in Greece
in the soil), it took many decades for the effects of soil
and many locations in the Middle East (such as present-
degradation to become evident.
day Israel, Jordan, Iraq, and Lebanon). This led either
The extent of erosion on a worldwide basis is
to colonial ventures to help feed the citizenry or to the
staggering—it is estimated that erosion has progressed
decline of the culture.
far enough to decrease yields on an estimated 16% of all
Tropical rainforest conditions (high temperature and
the world’s agricultural soils. The value of annual crop
rainfall, with most of the organic matter near the soil
loss due to soil degradation by erosion is around $1 bil-
surface) may cause significant soil degradation within
lion. And erosion is still a major global problem, robbing
two or three years of conversion to cropland. This is the
people of food and each year continuing to reduce the
reason the “slash and burn” system, with people moving
productivity of the land.
to a new patch of forest every few years, developed in the
tropics. After farmers depleted the soils in a field, they
HOW DO YOU bUIlD A HEAlTHY, HIgH-QUAlITY SOIl?
Some characteristics of healthy soils are relatively easy
to achieve—for example, an application of limestone
…what now remains of the formerly rich land is like the
will make a soil less acid and increase the availability of
skeleton of a sick man, with all the fat and soft earth
many nutrients to plants. But what if the soil is only a
having wasted away and only the bare framework
few inches deep? In that case, there is little that can be
remaining. Formerly, many of the mountains were
done within economic reason, except on a very small,
arable. The plains that were full of rich soil are now
garden-size plot. If the soil is poorly drained because of
marshes. Hills that were once covered with forests
a restricting subsoil layer of clay, tile drainage can be
and produced abundant pasture now produce only
installed, but at a significant cost.
food for bees. Once the land was enriched by yearly
We use the term building soils to emphasize that the
rains, which were not lost, as they are now, by flowing
nurturing process of converting a degraded or low-quality
from the bare land into the sea. The soil was deep, it
soil into a truly high-quality one requires understand-
absorbed and kept the water in the loamy soil, and the
ing, thought, and significant actions. This is also true
water that soaked into the hills fed springs and running
for maintaining or improving already healthy soils. Soil
streams everywhere. Now the abandoned shrines at
organic matter has a positive influence on almost all of
spots where formerly there were springs attest that
the characteristics we’ve just discussed. As we will discuss
our description of the land is true.
in chapters 2 and 8, organic matter is even critical for
—Plato, 4th Century b.C.e.
managing pests—and improved soil management should
be the starting point for a pest reduction program on
6
Building SoilS for Better CropS: SuStainaBle Soil ManageMent