Agriculture Reference
In-Depth Information
Chapter 8. Comparisons of conventional tillage and no-
till practices show increased earthworm abundance and
activity, diversification in soil-organic-matter-consum-
ing and -decomposing organisms, and an accompanying
improvement in soil structure, nutrient holding capacity,
internal nutrient cycling, and organic matter content
(House and Stinner, 1983; Stinner et al., 1984; Hendrix
et al., 1986). Even when the aboveground diversity of
the cropping system remains low, the species diversity
of the decomposer subsystem of the soil increases with
reduced soil disturbance. Increasing plant diversity
aboveground as well can only enhance this subsystem.
response may be a dramatic increase in the pest popula-
tion; only with time and the reestablishment of diversity
can internal mechanisms develop for keeping the pest in
check. An experimental framework for examining
the changes in diversity that occurs when a “pesticide
stress-free background” is established in a transitional
agroecosystem is presented in Chapter 20.
Integration of Livestock
Integrating animals back into the agricultural landscape
increases the overall biodiversity of the agroecosystem.
In addition, animal activity, such as grazing, crop residue
consumption, and manure deposition can alter aspects of
structural diversity, species dominance, and system func-
tion. Additional benefits accrue in the diversification
of the farm enterprise itself. Livestock integration is
discussed in more detail in Chapter 19.
High Organic Matter Inputs
High levels of organic matter are crucial for stimulating
species diversification of the belowground subsystem,
involving the same type of stimulation of structural and
functional diversity noted above for reduced tillage sys-
tems. Long seen as a key component of organic agricul-
ture, high organic matter inputs have an array of benefits
that were reviewed in Chapter 8. The organic-matter con-
tent of the soil can be increased by applying composts,
incorporating crop residues into the soil, cover cropping,
diversifying crops, and using other diversity-enhancing
cropping practices.
Managing Diversification
Moving from a uniform, monoculture agroecosystem to a
more diverse system supporting beneficial processes and
interactions is a multistep process. Initially, all of the
above ways of introducing diversity into the agricultural
landscape help mitigate the negative impacts of agri-
cultural activities. Then the introduction of more species,
either as a direct or indirect effect, broadens the opportu-
nities for integrated agroecosystem structure and function,
allowing built-in buffers and system dynamics to dampen
variability of system response. Finally, the kinds and
forms of interference in the diversifying landscape make
possible more types of interactions, ranging from com-
petitive exclusion to symbiotic mutualisms (summarized
in Table 16.3).
Managing diversity at the farm level is a big challenge.
Compared to conventional management, it can involve
more work, more risk, and more uncertainty. It also
Reduction in Use of Chemical Inputs
It has long been known that many agricultural pesticides
either harm or kill many nontarget organisms in crop
systems, or leave residues that can limit the abundance
and diversity of many other organisms. Thus, eliminating
or reducing the use of pesticides removes a major impedi-
ment to the rediversification of the agroecosystem. The
recolonization process involved in this rediversification is
discussed later in this chapter. It must be acknowledged,
however, that removing pesticides from a system that has
become dependent on them is a challenging task. The first
TA B L E 1 6 . 3
Methods of Increasing Ecological Diversity in An Agroecosystem
Dimensions of Ecological Diversity Affected
Method
Species
Genetic
Vertical
Horizontal
Structural
Functional
Temporal
Intercropping
•
o
•
•
•
•
o
Strip cropping
•
o
o
•
o
o
o
Hedgerows and buffers
•
o
•
•
o
o
•
Cover cropping
•
o
•
•
•
•
o
Rotations
o
o
—
—
o
o
•
Fallows
o
o
—
—
o
o
•
Minimum tillage
•
o
—
—
o
•
o
High inputs of organic matter
•
o
—
—
o
•
—
Reduction of chemical use
o
o
—
—
o
•
—
Integration of livestock
•
o
—
o
o
•
o
• denotes direct or primary effect; o denotes Indirect, secondary, or potential effect; — denotes little or no effect
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