Environmental Engineering Reference
In-Depth Information
4.3
Organic Manures
tant structure that may be viewed as long-term
propagules in the absence of a viable host,
hyphae are considered to be the main source of
inocula for plants in undisturbed soils. The dam-
age to these hyphal networks by tillage not only
affects AM fungal growth but also reduces root
colonization due to death or lowers infectivity
of the hyphal fragments compared with intact
hyphal networks (Johnson et al.
2001
; Garcia
et al.
2007
).
Different AM fungi responded variedly to dif-
ferent tillage management practices (Gálvez
et al.
2001
; Kabir
2005
; Borie et al.
2006
). Tillage
can reduce the root length colonized by AM
fungi and subsequently AM-mediated P, Zn and
Cu uptake by plants (Mozafar et al.
2000
; Goss
and de Varennes
2002
). Certain AM fungal spe-
cies may survive in tilled soils, while others may
disappear. Because AM fungi are more abundant
in the topsoil, deep ploughing may dilute their
propagules in a greater volume of soil, thereby
reducing their chance of association with a plant
root. Soil aggregation is an important process
that maintains soil porosity, hydraulic activity,
organic matter and also soil erosion (Caesar-
TonThat et al.
2011
). But these processes are dis-
turbed by long-term tillage systems, which
subsequently not only affects the carbon stabili-
zation and sequestration but also the microbial
populations (Sainju et al.
2009
). In undisturbed
soil, roots follow preformed channels, making
close contact with the AM-colonized root sys-
tems of the previous crop, resulting in enhanced
mycorrhization of roots (Evans and Miller
1990
).
Furthermore, no-tillage favours the accumulation
of organic matter, changes in soil structures and
increased availability of C, N and water (Doran
and Linn
1994
; Shirani et al.
2002
) in the surface
horizons, thereby maximizing their benefi ts to
crops (Kabir et al.
1999
). Sheng et al. (
2012
)
showed that long-term tillage and P fertilization
invertedly affected the fi ne root development and
AM fungal colonization in corn roots. In a recent
study, Schalamuk et al. (
2013
) demonstrated that
the effect of no-tillage or conventional tillage
system on the abundance of AM fungal propa-
gules in wheat crops depends more on the pheno-
logical stages of the crop.
Organic manure consists of materials of bio-
logical origin which are used to restore the soil
fertility and plant growth. According to Lee
et al. (
2008
), general principles of organic
farming include (1) exclusion of synthetic bio-
cides; (2) addition of organic fertilizers to the
soil, including farmyard manure, compost and
crop residue and slow-release mineral fertiliz-
ers such as rock phosphate; and (3) use of crop
rotation (IFOAM
1998
). Manure application
may increase or decrease root colonization by
AM fungi. Tarkalson et al. (
1998
) found that
manure application increased AM colonization,
P and Zn uptake by plants and crop yield.
Muthukumar and Udaiyan (
2000
) showed that
manure applications could increase spore popu-
lations and root colonization by AM fungi.
Gaur and Adholeya (
2000
) also found that
organic amendments supported both high crop
yield and AM fungal populations in onion, gar-
lic (
Allium sativum
) and potato. The benefi t of
organic amendment on AM fungi has been
attributed to changes in soil structure with
manure amendments like increased porosity,
enlarged mean weight diameter of aggregates,
improved water retention capacity and greater
activity of benefi cial soil microbes in the soil
profi le (Celik et al.
2004
; Pagliai et al.
2004
).
However, the effects of compost application on
AM colonization appear to be inconsistent
(Ellis et al.
1992
; Allen et al.
2001
). For exam-
ple, the low levels of root colonization by AM
fungi in soybean and sorghum in compost-
amended soils were attributed to high soil P
availability (Garcia et al.
2007
). Muthukumar
and Udaiyan (
2002
) showed that the growth and
yield of the cowpea (
Vigna unguiculata
) varied
in response with various organic amendments
based on changes in indigenous AM fungal
populations.
The response of plants to AM fungal inocula-
tion in organic-amended soils has been shown to
either increase (Rydlová and Vosátka
2000
;
Gryndler et al.
2002
,
2006
) or decrease
(Ravnskov et al.
1999
,
2006
). Composted
organic amendments in soil promote AM fungal
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