Agriculture Reference
In-Depth Information
and numbers of specifi c species are important. However evidence suggests that these
basic soil health test kits provide useful guidance to help farmers with soil management
decisions.
There is increasing evidence of the impact which composts and compost extracts and
teas can have on soil health and the presence of benefi cial microorganisms (Abawi &
Widmer, 2000; Albiach
et al
., 2000; van Bruggen & Semenov, 2000; van Bruggen &
Termorshuizen, 2003). This is considered further in the following sections.
5.7
Effects of composts on plant disease
Composts have been applied to agricultural land world-wide for centuries, but their
deliberate application for the purpose of preventing and controlling plant diseases is a
more recent phenomenon. The majority of published work relating to the use of composts
and compost extracts or teas for prevention and control of diseases involves the produc-
tion of plants in containers in controlled environments (growth rooms or glasshouses)
using composts mixed with soil, sand or peat. However, there is increasing interest in the
potential for composts and similar materials to help prevent and control diseases in fi eld
crops and information on the use of composts in fi eld trials is slowly increasing. Work
to determine the effects of composts on plant diseases in container, glasshouse and fi eld
production systems has recently been comprehensively reviewed (Litterick
et al.,
2004;
Noble & Coventry, 2005).
5.7.1
Container media
Numerous studies have examined the potential for composts to control or suppress
diseases in plants grown in media based partly on compost (along with sand, soil or
peat), or more rarely, made solely from compost. Most work has concentrated on one
or more of the root and stem-base pathogens:
Pythium ultimum, Phytophthora
spp.,
Rhizoctonia solani
or
Fusarium oxysporum
. Reports concern the effects of composts
on ornamentals (including hardy nursery stock and pot plants) and container-produced
edible crop plants (such as radish, cucumber, tomato, pea, pepper and brassicas).
Input materials (or feedstocks) in composts found to suppress plant pathogens include
hardwood and softwood bark, animal manures (pig, poultry, horse and cattle), veg-
etable wastes, green (or yard) wastes, sewage sludge (or municipal solid waste) and
fi sh wastes. Workers using these composts have demonstrated suppression of root and
soil-borne pathogens (and occasionally foliar diseases) on a range of crops. However,
levels of disease suppression were not consistent for individual feedstocks and they
were found to differ both between and within studies.
It is diffi cult to compare different pieces of work, since experimental conditions varied
widely, but it is possible to assess which feedstocks may be considered for some crop/
disease applications. For example,
Rhizoctonia solani
and
Sclerotium rolfsii
were
suppressed in container media containing composted separated cattle manure and
composted grape marc (Gorodecki & Hadar, 1990).
Pythium aphanidermatum
damping-
off was suppressed in container media containing composted liquorice roots (Hadar &
Mandelbaum, 1986) and disease caused by
Pythium ultimum
and
Rhizoctonia solani
was
controlled or considerably reduced in container media amended with composted organic
