Agriculture Reference
In-Depth Information
obtained by fermentation of compost carried out on liquid phase, in commercial or
rudimental brewers, for a few days or up to 2 weeks, with or without active aeration,
so as to produce aerated (ACTs) or non-areated (NCTs) compost teas, respectively
(Ingham
1999
; Lanthier
2007
). Usually, also the compost extracts obtained by fil-
tration of an aqueous suspension, after just a few hours of mixing, are referred as
teas (Joshi et al.
2009
). There are number of reports that demonstrate the ability of
compost teas to suppress a wide range of plant pathogens, when applied as foliar
spray and soil drenching (Scheuerell and Mahaffee
2002
,
2004
). Compost teas may,
in fact, contain organic and inorganic soluble molecules, such as humic substances,
phytochemicals and a large number of useful organisms, including bacteria, fungi,
protozoa and nematodes, which may provide benefits for the vigor and health of
the plants (Scheuerell and Mahaffee
2002
). Composting pile-percolating leachates
has been also proposed to reach the described scope (ROU
2006
); but the risks
deriving from a possible contamination by kinds of anaerobic human pathogens,
gave restrictions to the use. A number of factors, which are involved in the compost
extraction process, influencing the microbiological and chemical components of
compost teas, are responsible for their efficacy in plant disease suppression. Firstly,
a quality compost with good suppressive properties has the potential to make a
high-quality compost tea, if made with proper preparation methodologies. The hy-
pothesized mechanisms to explain compost teas ability in controlling plant diseases
are similar to those viewed above for suppressive composts. In addition, compost
teas contribute indirectly to the protection by inciting an improved physiological
and vegetative status in the plants, making their less susceptible to pathogen attacks.
Several nutritional and hormone-like substances suspended in the teas are believed
to act in this direction. Compost tea suppressivity is ascribed, essentially, to its
biotic component that has an antagonistic activity against pathogens (Noble and
Coventry
2005
; Pane et al.
2011
,
2012b
) and/or incite systemic resistance response
in treated plants (Siddiqui et al.
2009
). For these reasons, compost tea production
techniques are based on the regulation of some parameters, such as ratio of compost
to water, oxygenation levels, duration and temperature of fermentation, to generate
conditions more favorable to the presence and development of beneficial organ-
isms in the final product. In this context, the amendment of aqueous extractant
with fermentation nutrients, such as food industry waste (such as molasses, borland,
casein, whey, etc.), was also proposed in order to condition the microbiological
characteristics of the teas. The introduced nutrients place selective pressure on the
microbial community can potentially increase biological control agents that inhabit
the compost tea.
8.8
Conclusion
Suppressivity should be viewed as an added value with a significant impact on
crop management, because the use of disease suppressive compost will reduce
crop losses caused by diseases. Such property made possible a global sustainable
