Environmental Engineering Reference
In-Depth Information
propagules per bed, 40-fold lower than the
3-year method (method 2).
additions are unnecessary during inoculum
production.
5.2.4 Method 4
In 2005, Douds et al. developed another method
for on-farm production of AM fungal inoculum
for temperate regions. Raised bed enclosures
(0.75 × 3.25 × 0.3 m) were constructed with silt
fence walls, weed barrier cloth fl oors and plastic
sheeting dividing walls dividing the enclosure
into 0.75 m square sections. The enclosures were
fi lled to a depth of 20 cm with a 1:4 (v/v) mixture
of compost and vermiculite. Pre-colonized ten
Bahia grass plants were transplanted into the
enclosures. One AM fungal isolate was used per
enclosure section. The enclosures were tended
for one growing season and watered as needed
(Douds et al.
2005
).
5.2.6 Method 6
In 2010, Douds et al. modifi ed the existing method
for the production of AM fungal inoculum in tem-
perate climates. Black plastic bags fi lled with
approximately 20 L of a 1:4 (v/v) mixture of pas-
teurized compost and vermiculite served as the
growing medium. To this growing medium, fi eld
soil (containing 12 propagules cm
−3
) collected
from the top 10 cm from a fi eld was mixed at the
rate of 100, 200 or 400 cm
3
. Three-month-old
non-mycorrhizal or mycorrhizal Bahia grass
seedlings were planted in the bags at a rate of fi ve
plants per bag and grown for 3 months. Adding
100 cm
3
of fi eld soil to the growing medium and
planting with non-mycorrhizal seedlings pro-
duced 465 propagules cm
−3
compared to 137
propagules cm
−3
for planting with the pre-colo-
nized seedlings (Douds et al.
2010
).
5.2.4.1 Advantage
The advantage of this method includes the pro-
duction of signifi cant quantities of the desired
AM fungi. An average of 95 × 10
6
propagules
could be produced per 0.75 × 0.75 m enclosure
section.
5.2.6.1 Advantage
This modifi cation to the existing method allows
greater fl exibility and makes it easier for the
production of the AM fungal inoculum directly
on the farm. This method could be readily
adopted by farmers.
5.2.5 Method 5
In 2006, Douds et al. suggested another method
for on-farm production of AM fungus inoculum.
Bahia grass seedlings colonized by AM fungi
were transplanted into raised bed enclosures con-
sisting of vermiculite mixed with either fi eld soil
or yard clipping compost or vermiculite mixed
with yard clipping compost or dairy manure/leaf
compost. The propagule yield was higher in com-
post and vermiculite mixture compared to soil-
based mixture. Inoculum production in a 1:4
(v/v) mixture of yard clipping compost and ver-
miculite media was more (503 propagules cm
−3
)
than those with 1:9 and 1:99 (v/v) mixtures (240
and 42 propagules cm
−3
), respectively (Douds
et al.
2006
).
6
Determination of Infective
Propagule Abundance
The most suitable and convenient method to
determine the number of infective propagules of
AM fungi in a crude inoculum, soil or mycorrhi-
zal root bits is termed as the most probable num-
ber (MPN) technique (Alexander
1982
). It has
been assessed by using a statistical estimation of
microbial population density (Cochran
1950
).
6.1
Inoculum Management
5.2.5.1 Advantage
This method enables the production of concen-
trated AM fungal inoculum that can be readily
used in horticultural potting media for vegeta-
ble seedling production. Supplemental nutrient
Inoculum formulation procedure consists of plac-
ing fungal propagules (root fragments, mycelium
and spores) in a carrier (perlite, peat, inorganic
clay, zeolite, vermiculite, sand, etc.) for a given
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