Agriculture Reference
In-Depth Information
stable
nonstable
fresh
casts
Time
FIGURE 20.8
Timing of the vermicomposting process. There are no data on when a vermicompost can
be considered optimum, on how this optimum can be determined, and if this optimum has some kind of
Ñexpiration date.Ò
be because of adverse growth factors, such as high levels in 100% vermicomposts, particularly
those from animal wastes.
In spite of all this research on the effects of vermicomposts on plant growth, there are still few
data in the literature validating possible mechanisms by which vermicomposts produce these growth
enhancement effects.
V
ERMICOMPOSTS
AS
S
UPPRESSORS
OF
P
LANT
D
ISEASES
AND
P
LANT
-P
ARASITIC
N
EMATODES
Although there are not many studies regarding vermicomposts as suppressors of plant diseases and
plant-parasitic nematodes, it has been shown that the incidence of plant diseases can be limited by
vermicomposts. Substrates supplemented with vermicompost were suppressive to root rot of tomato
caused by
Phytophthora nicotiane
var.
nicotianae,
and dipping cabbage roots in a mixture of clay
and vermicompost decreased infection by
Plasmodiophora brassicae
(Szczech et al. 1993); they
also reduced infection of tomato plants by
Fusarium oxysporum
f. sp.
lycopersici
(Szczech 1999).
Vermicompost at a concentration of 40 Hg/ml caused a 50% reduction of zoosporangia formation
of
Phytophthora cryptogea,
and amendment of soil extract with 1000 Hg ml
−1
of vermicompost
completely inhibited the pathogen sporulation. Peat drenched with vermicompost extracts imme-
diately after planting of gerbera, ivy, carnation, or cyclamen significantly suppressed the spread of
diseases. The compound applied at a concentration of 25% caused a decrease of about 50% of
propagule numbers of
Fusarium oxysporum
f. sp.
dianthi
in peat naturally infested with the pathogen
(Orlikowski 1999). Vermicompost incorporation at a 20% rate reduced the incidence of diseased
plants of gerbera (
Gerbera jamesonii
H. Bolus), the area under the disease progress curve, and the
disease growth rate of the fungi
Rhizoctonia
solani
,
Phytophthora drechsleri,
and
Fusarium
oxysporum
(Rodrguez et al. 2000). Chaoui et al. (2002) demonstrated suppression of
Pythium,
Rhizoctonia
, and
Verticillum
by vermicomposts. Arancon et al. (2002, 2003) demonstrated consis-
tent suppression of plant-parasitic nematode populations by vermicomposts under pepper, tomatoes,
strawberries, and grapes in the field.
