Environmental Engineering Reference
In-Depth Information
crops, which in the rotation follow non-host
plants (or plants, which develop little mycorrhi-
zal colonization), may carry less colonization
than they would follow a strongly mycorrhizal
crop (Ocampo and Hayman
1981
). The composi-
tion of AM fungal spore communities tends to
change signifi cantly if crop rotation was prac-
ticed along with P fertilization (Mathimaran et al.
2007
). According to Vestberg et al. (
2005
),
improved P nutrition of rice grown under acidic
and phosphorus defi ciency conditions without
using P fertilizer could be achieved by crop rota-
tion (maize and horse gram) along with AM fun-
gal inoculation.
that the absence of host roots could drastically
reduce AM fungal populations in the soil. The
fi ndings of Troeh and Loynachan (
2003
) suggest
that continuous cropping of maize and soybean
increases AM fungal spore numbers, whereas
spore numbers tend to decrease under fallow.
Recently, Karasawa and Takebe (
2012
) reported
that fallow condition could reduce the abundance
of AM fungal propagules (spores and mycelium),
due to the disruption of AM fungal mycelial net-
work and alteration of available nutrients and
microbial activities in soil (Jansa et al.
2003
). To
overcome the defects, the maintenance of high
AM fungal abundance in cropping systems could
ensure tolerance to prolonged fallow periods and
their activity (Hijri et al.
2006
).
4.6
Fallow Period
4.7
Management Considerations
Fallow, the reinstatement period to trim down the
weed growth, may negatively infl uence AM
fungi. Crops including corn, sorghum, sunfl ower,
chickpea and linseed, when grown in southern
Queensland, Australia, after long periods of bare
fallow, exhibited poor growth with P and Zn defi -
ciency. This syndrome, termed long-fallow disor-
der, was associated with low AM colonization,
failure of AM fungal mycelia networks in soil to
take up suffi cient nutrients and reduced AM
fungal spore density and diversity (Kabir and
Koide
2000
; Karasawa et al.
2002
). The applica-
tion of P and Zn fertilizers to soils following long
fallow not only alleviated the negative effects of
low AM colonization and fertility, but crops
responded better than in soils with higher AM
fungal inoculum levels (Thingstrup et al.
1998
).
Poor growth of linseed after prolonged fallowing
in a semiarid cropping system was improved by
inoculation with AM fungal propagules obtained
from sorghum-cropped fi eld soil (Thompson
1994
). A 1-year fallow in an oxisol reduced the
number of AM fungal propagules by 40 % and
the growing of non-mycorrhizal crops like mus-
tard (
Brassica juncea
) reduced them by 13 %
(Harinikumar and Bagyaraj
1988
). Wagner et al.
(
2001
) observed an exponential decline in spore
counts of
Claroideoglomus claroideum
(
=Glomus
claroideum
) with time during soil storage. with
time during soil storage. Ellis (
1998
) also showed
Reports of improved plant growth responses in
response to AM inoculation under controlled con-
ditions in low fertile soils led to a fl urry of activi-
ties during 1980s, aimed at utilizing AM fungi as
bioinoculants. However, the magnitude of
responses was different under fi eld conditions,
especially under conventional high-input agricul-
tural systems. Further studies, however, have
shown that most crop species are mycorrhizal and
AM fungi can have a substantial positive or nega-
tive impact on crop productivity (Johnson et al.
1997
). Therefore, there is a need to elucidate the
role of AM fungi in agroecosytems and to under-
stand the impact of management practices on the
symbiosis. The introduction of appropriate fungi
to the plant production systems may be appropri-
ate under conditions where the native AM fungal
inoculum potential is low or ineffi cient. The ini-
tial step in any inoculation programme is to iden-
tify and isolate organisms that are both infective
(able to associate) and effective (able to impart
desired effects) under a given set of conditions.
Isolates of AM fungi may vary widely in these
properties. So, screening trials are needed to
select isolates that will perform effi ciently and
successfully. Screening under actual fi eld condi-
tions is preferred than under controlled condi-
tions, because the infl uence of indigenous AM
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