Agriculture Reference
In-Depth Information
13.1.3 Tillage/Residue Management
species, particularly root morphology, as well as
soil and climate (Muchovej
2001
). Crops with
thick roots, poorly branched, and with few root
hairs are more dependent on mycorrhizae includ-
ing onions, grapes, citrus, cassava, coffee, and
tropical legumes.
In many parts of the world, phosphate fertil-
izers are relatively inexpensive, and therefore
farmers do not have a great incentive to inoculate
with mycorrhizae. Where phosphate fertilizers
are relatively expensive or unavailable, the lack
of commercial inoculums and the diffi culty of
culturing one's own are signifi cant barriers,
although commercial sources are becoming
available.
Inoculation with ectomycorrhizae is common
in the forest industry, but the necessity for more
diffi cult to produce arbuscular mycorrhizae has
slowed penetration into agriculture. Nevertheless,
practical applications include transplant media
that have been treated to remove soil pathogens,
revegetation of eroded or mined areas, and in arid
and semiarid regions (Muchovej
2001
).
(i)
Advantages
• Mycorrhizal-inoculated plants produce
larger biomass as a direct consequence
of improved photosynthetic activities,
and they can translocate 20-30 % of
assimilated carbon to the rhizosphere
(underground).
• Glomalin concentrations in the soil can be
signifi cantly enhanced by the mycorrhizal
inoculation resulting in more durable soil
carbon sequestration, as well as more sta-
ble soil aggregates with improved soil
physical properties.
(ii)
Disadvantages
• Indigenous mycorrhizal fungal inocula-
tion is not very effective and causes inhib-
itory effects when inorganic fertilizer is
applied to the soil without any integration
of organic manures.
• Cultures of arbuscular mycorrhizae for
inoculation of agricultural crops require a
host plant and therefore are diffi cult to
grow. However, they are beginning to
become commercially available, at least
in the USA (Muchovej
2001
) .
No-tillage systems can reduce greenhouse gas
emissions in a variety of ways. The same is true
for minimal tillage (also called reduced tillage)
systems but to a lesser extent. While previously
tillage was an essential feature of farming,
advances in weed control methods and farm
machinery now allow many crops to be grown
with minimal or no-tillage. These practices are
now increasingly used throughout the world
(Cerri et al.
2004
).
Soil disturbances tend to stimulate soil carbon
loss through enhanced decomposition and
erosion. Therefore, reducing soil disturbances
through minimal tillage or no-tillage systems
reduces soil carbon losses. In addition, no-tillage
or minimal tillage systems may affect N
2
O
emissions. However, the net effects on N
2
O emis-
sions are not yet well-quantifi ed (IPCC
2007c
).
The effect of reduced tillage on N
2
O emissions
may depend on soil and climatic conditions. In
some areas, reduced tillage promotes N
2
O
emissions, while elsewhere it may reduce emis-
sions or have no measurable infl uence (Marland
et al.
2001
). No-tillage systems can also reduce
greenhouse gas emissions from energy use.
Residue management in the form of the retain-
ment of crop residues also tends to increase soil
carbon storage. Increased soil carbon storage
occurs as the residue is the precursor for soil
organic matter, which is the main carbon store in
the soil. Moreover, avoiding the burning of resi-
dues also avoids emissions.
13.1.3.1 Conservation Tillage
Conventional tillage is the traditional method of
farming in which soil is prepared for planting by
completely inverting it with a tractor-pulled plow,
followed by subsequent additional tillage to
smooth the soil surface for crop cultivation. In
contrast, conservation tillage is a tillage system
that conserves soil, water, and energy resources
through the reduction of tillage intensity and
retention of crop residues. Conservation tillage
involves the planting, growing, and harvesting of
crops with limited disturbance to the soil
surface.
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