“Whatever the cause of soil unthriftiness, there is no
and find new sources of residues to add to soils. New
dispute as to the remedial measures. Doctors may
residues can include those you grow on the farm, such
disagree as to what causes the disease, but agree as to
as cover crops, or those available from various local
the medicine. Crop rotation! The use of barnyard and
sources. Second, try to use a number of different types
green manuring! Humus maintenance! These are the
of materials—crop residues, manures, composts, cover
fundamental needs” (Hills, Jones, and Cutler, 1908). A
crops, leaves, etc. It is important to provide varied
century later, these are still some of the major remedies
residue sources to help develop and maintain a diverse
available to us.
group of soil organisms. Third, although use of organic
There seems to be a contradiction in our view of soil
materials from off farm can be a good source for build-
organic matter. On one hand, we want crop residues,
ing soil organic matter and adding nutrients, some farm-
dead microorganisms, and manures to decompose. If
ers overload their fields with excess nutrients by excess
soil organic matter doesn’t decompose, no nutrients
imports of organic materials. Crop residues (including
are made available to plants, no glue to bind particles
cover crops) as well as on-farm-derived animal manures
is manufactured, and no humus is produced to hold
and composts help to supply organic materials and
on to plant nutrients as water leaches through the soil.
cycle nutrients without a buildup of excessive levels of
On the other hand, numerous problems develop when
nutrients. Fourth, implement practices that decrease the
soil organic matter is significantly depleted through
loss of organic matter from soils because of accelerated
decomposition. This dilemma of wanting organic matter
decomposition or erosion.
to decompose, but not wanting to lose too much, means
All practices that help to build organic matter levels
that organic materials must be continually added to the
either add more organic materials than in the past or
soil. A supply of active organic matter must be main-
decrease the rate of organic matter loss from soils. In
tained, so that soil organisms have sufficient food, and
addition, practices to build organic matter will usually
so that humus can continually accumulate. This does not
enhance beneficial organisms and/or stress pests (table
mean that organic materials must be added to each field
9.1). Those practices that do both may be especially
every year—although that happens to a greater or lesser
useful. Practices that reduce losses of organic matter
degree if crop roots and aboveground residues remain.
either slow down the rate of decomposition or decrease
However, it does mean that a field cannot go without
the amount of erosion. Soil erosion must be controlled
a significant quantity of organic residue additions for
to keep organic matter–enriched topsoil in place. In
many years without paying the consequences.
addition, organic matter added to a soil must either
Do you remember that plowing a soil is similar to
match or exceed the rate of loss by decomposition.
opening up the air intake on a wood stove? What we
These additions can come from manures and composts
really want in soil is a slow, steady burn of the organic
brought from off the field, crop residues and mulches
matter. You get that in a wood stove by adding wood
that remain following harvest, or cover crops. Reduced
every so often and making sure the air intake is on a
tillage lessens the rate of organic matter decomposition
medium setting. In soil, you get a steady burn by adding
and also may result in less erosion. When reduced tillage
organic residues regularly and by not disturbing the soil
increases crop growth and residues returned to soil, it is
too often or too greatly.
usually a result of better water infiltration and storage
There are four general strategies for organic matter
and less surface evaporation. It is not possible in this
management. First, use crop residues more effectively
book to give specific management recommendations for
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Building SoilS for Better CropS: SuStainaBle Soil ManageMent