Agriculture Reference
In-Depth Information
specifically focusing on the effects of fire frequency on
arthropod populations are still rare.
In agroecosystems, even less is known about pest
management in relation to fire. Many insect pests can pass
the time between cropping seasons in some part of the
plant, either living or dead, left over from the previous
season. Bollworm problems in cotton are dramatically
reduced if all plant residue is destroyed, and fire is one
tool for achieving this end. Stemborers in grain crops
overwinter in straw remaining in the field after harvest,
and appropriate use of fire might aid in their management.
For ground-dwelling arthropod pests, fire that pene-
trates the soil surface can be a useful method of pest
management. Burning mulch or crop residues, and artifi-
cial flaming of the soil surface, are ways of introducing
fire for this purpose.
A traditional practice that uses fire to protect a crop
from insect damage is known from Tabasco, Mexico
(Figure 10.8). A large Coleopteran beetle has a reputation
for being able to invade a bean planting and defoliate the
crop in a very short period of time. The beetles invade in
large numbers and can be seen consuming the plant leaves
in the early morning hours. Farmers report that an old
practice was to come into the infested field in the morning,
collect enough of the live beetles to place 25 to 50 of them
in each of several fire-resistant containers. At the end of
the day, each container was placed over a fire long enough
to kill the insects but not to burn them. Shortly thereafter,
the open containers were partly buried in the soil in the
bean field, about one to every 400 m 2 . By the next morning,
farmers report, there were no signs of living or actively
feeding beetles in the field. An alarm pheromone released
by the dying beetles is suspected of alerting living beetles
to danger so they leave the field, but further research is
needed. Farmers have stopped using this practice since
synthetic chemical pesticides have been introduced.
fire as tool to fight this disease (Moritz and Odion, 2005).
It is interesting to note that the burning of grass fields, a
practice that has become very important in fields used to
produce commercial grass seed in the Pacific Northwest
region of the U.S., was started originally for the purpose of
disease control in the late 1940s.
Heat and desiccation probably have the greatest direct
impact on pathogenic organisms. The high temperatures
registered at the soil surface during a fire, and the pene-
tration of heat down to several centimeters below the
surface, can kill large numbers of living pathogens and
their inoculum. In addition, the sudden increase in pH
caused by the wetting of ash deposited on the soil after a
fire can have an inhibitory affect on fungi, since fungi
prefer neutral to acid conditions for optimal development.
Many bacteria, on the other hand, are actually stimulated
by the higher pH, and might become more of a problem
if they are pathogenic.
The effect of burning above-ground plant material,
especially crop residues, on potential plant pathogens is
well documented. Since a well-managed fire can consume
as much as 95% of the above-ground biomass and generate
extreme heat, it can kill most pathogens present in the
biomass. This effect of fire is the most common reason
for burning crop residues, as described above.
Preparing a Crop for Harvest
Fire can be used to prepare a crop for harvest. A common
example is the burning of sugar cane fields a few days
ahead of harvest of the canes. Cane cutters claim that fire
is important for removing the leaves from the stems, facili-
tating the cutting process when done by hand, making
access to the canes easier, and displacing bothersome ani-
mals such as rats and snakes. But ease of harvest in such
a system has to be weighed against ecological impacts
such as loss of organic matter, volatilization of certain
nutrients, and nutrient leaching with heavy rainfall. For
sugar cane in particular, another possible negative impact
of fire may be to degrade the quality of the sugar extracted
from overheated canes.
Another simple role for fire at harvest time is in the
collection of pine nuts. Cones of several pinyon pine
species are collected from trees before they open and
disperse their seeds (called nuts). Usually the cones are
coated by dense pitch. Fire is used to heat rocks that are
then placed with the cones, melting away the pitch and
opening the cones to release the seed. Fire can also be
used to heat an oven into which the pitch-covered cones
can be placed.
Pathogen Management
Because of fire's ability to elevate temperatures in the soil,
especially close to the surface, fire should be expected to
have a significant impact on plant pathogens living in the
soil, such as fungi, bacteria, and nematodes. Relatively little
research has been done on the effect of fire in relation to
plant disease management, but in a review done some years
ago (Hardison, 1976), it was found that fire could effectively
reduce inoculum of diseases of various forest crops, fruits,
ornamentals, cotton, potatoes, small grains, and grasses and
forages. In a recent study investigating the relationship
between fire and Sudden Oak Death Disease ( Phytophthora
ramorum ), researchers found that infections were extremely
rare within areas that had been burned in the last 50 years.
However, the mechanisms underlying these results were not
completely understood and the authors pointed to the need
for more research in order to better understand the use of
Pasture and Range Management
Despite the fact that in most grassland areas of the world,
natural fire is frequent and an important aspect of the
environment, the effective use of fire as a tool for managing
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