Many of the practices that build up and maintain soil
The role of diversity is critical to maintaining a well-
organic matter enrich the soil with nutrients or make
functioning and stable agriculture. Where many differ-
it easier to manage nutrients in ways that satisfy crop
ent types of organisms coexist, there are fewer disease,
needs and are also environmentally sound. For example,
insect, and nematode problems. There is more competi-
a legume cover crop increases a soil’s active organic
tion for food and a greater possibility that many types of
matter and reduces erosion, but it also adds nitrogen
predators will be found. This means that no single pest
that can be used by the next crop. Cover crops and deep-
organism will be able to reach a population high enough
rooted rotation crops help to cycle nitrate, potassium,
to cause a major decrease in crop yield. We can promote
calcium, and magnesium that might be lost to leaching
a diversity of plant species growing on the land by using
below crop roots. Importing mulches or manures onto
cover crops, intercropping, and crop rotations. However,
the farm also adds nutrients along with the organic
don’t forget that diversity below the soil surface is as
materials. However, specific nutrient management prac-
important as diversity above ground. Growing cover
tices are needed, such as testing manure and checking
crops and using crop rotations help maintain the diversity
its nutrient content before applying additional nutrient
below ground, but adding manures and composts and
sources. Other examples of nutrient management prac-
making sure that crop residues are returned to the soil are
tices not directly related to organic matter management
also critical for promoting soil organism diversity.
include applying nutrients timed to plant needs, liming
acidic soils, and interpreting soil tests to decide on the
bESIDES ORgANIc MATTER MANAgEMENT
appropriate amounts of nutrients to apply (see chapters
Although enhanced soil organic matter management
18 to 21). Development of farm nutrient management
practices go a long way to helping all aspects of soil
plans and watershed partnerships improves soil while
health, other practices are needed to maintain an
also protecting the local environment. And as discussed
enhanced physical and chemical environment. Plants
above, it is possible to overload soils with nutrients
thrive in a physical environment that allows roots to
by bringing large quantities of organic materials such
actively explore a large area, gets all the oxygen and
as manures or composts from off the farm for routine
water needed, and maintains a healthy mix of organ-
annual applications.
isms. Although the soil’s physical environment is
strongly influenced by organic matter, the practices and
SUMMARY
equipment used—from tillage to planting to cultivation
Improved soil organic matter management is at the
to harvest—have a major impact. If a soil is too wet—
heart of building better soils—creating a habitat below
whether it has poor internal drainage or receives too
the ground that is suited to optimal root development
much water—some remedies are needed to grow high-
and health. This means adding adequate annual quanti-
yielding and healthy crops. Also, erosion—whether by
ties, tons per acre, of a variety of organic materials—
wind or water—is an environmental hazard that needs to
crop residue, manure, composts, leaves, etc.—while not
be kept as low as possible. Erosion is most likely when
overloading the soil with nutrients from off the farm. It
the surface of a soil is bare and doesn’t contain sufficient
also means reducing the losses of soil organic matter as
medium- to large-size water-stable aggregates. Practices
the result of excess tillage or erosion. But we’re not just
for management of soil physical properties are discussed
interested in the amount of organic matter in soil. Even
in chapters 14 to 17.
if the organic matter content of the soil doesn’t increase
97
Building SoilS for Better CropS: SuStainaBle Soil ManageMent