Agriculture Reference
In-Depth Information
et al. (2000), who demonstrated that there were exchangeable auxin groups in the macrostructure
of humic acids extracted from vermicomposts. These workers also showed that these complexes
influence lateral root development of maize. This research provided valuable clues why vermicom-
posts influence plant germination, growth, flowering, and yields so dramatically over and above
their content of readily available nutrients and make positive contributions to soil structure and
fertility.
Thus, there is increasing evidence of the various ways in which components of vermicomposts
can increase the germination, growth, flowering and fruiting of a wide range of crops as discussed
in this chapter. This also has implications for organic farming, for if earthworms can promote the
activity and effects of PGRs in organic wastes, it may also be true that in soils to which organic
matter is added, the production of PGRs by microorganisms may be increased by soil-inhabiting
earthworm activity.
EFFECTS OF VERMICOMPOSTS ON PLANTS: THE INCIDENCE OF
PLANT PATHOGENS, PLANT-PARASITIC NEMATODES, AND
ARTHROPOD PESTS
The suppression of plant pathogens by organic matter and thermophilic composts (Hoitink and
Grebus 1997) and plant-parasitic nematodes by various forms of organic matter is well documented
(Akhtar and Malik 2000). There are many unsubstantiated reports in the popular organic literature
of the control of pests by organic matter application. However, only recently has the potential of
vermicomposts in the suppression of pests been explored.
P
LANT
D
ISEASES
There is extremely extensive literature on the suppression of plant diseases by organic amendments
(Ara et al. 1996; Arafa and Mohammed 1999; Bettiol et al. 1997, 2000; Blok et al. 2000; Chen et
al. 1987; Cotxaterra et al. 2001; Dixon et al. 1998; Diyora and Khondar 1995; Dutta and Hegde
1995; Ehteshamul et al. 1998; Fikre et al. 2001; Goldstein 1998; Goudar et al. 1998; Harender et
al. 1997; Hoitink and Kuter 1986; Hoitink et al. 1997; Kannangowa et al. 2000; Karthikeyan and
Karunanithi 1996; Lazarovits et al. 2000; Lima et al. 1997; Nam et al. 1988; Panneerselvam and
Saravanamuthu 1996; Pitt et al. 1998; Raguchander et al. 1998; Rajan and Sarma 2000; Ramamoor-
thy et al. 2000; Sanudo and Molina-Valero 1995; Schiau et al. 1999; Somasekhara et al. 2000;
Velandia et al. 1998) and traditional thermophilic composts (Hoitink et al. 1997; Huelsman and
Edwards 1998). Various mechanisms have been suggested for this suppression, but most of these
are based on some form of microbial antagonism.
Traditional composting is a thermophilic process that promotes microbial activity selectively,
whereas vermicomposting is a nonthermophilic method and promotes greatly increased activity by
a wide range and diversity of microorganisms. We have considerable evidence from our research
at OSU of much greater microbial activity and biodiversity in vermicomposts than in thermophilic
composts. Our laboratory and field research provide evidence that vermicomposts may have an
even greater potential for disease suppression than traditional thermophilic composts. For instance,
general observational evidence of decreases in plant disease incidence and of pathogen suppression
were recorded in studies involving 28 species of crop plants grown in vermicomposts (Edwards
and Burrows 1988; Scott 1988).
Nakamura (1996) reported suppression of
Plasmodiophora brassicae, Phytophthora nicoti-
anae
(tomato late blight), and
Fusarium lycopersici
(tomato fusarium wilt) by vermicomposts.
Szczech (1999) and Szczech et al. (2002) reported vermicompost suppression of
Fusarium
lycopersici
and
Phytophthora nicotianae
on tomatoes. Rodrguez et al. (2000) demonstrated
general suppression of fungal diseases of gerbera plants such as
Rhizoctonia solani
,
Phytophthora
drechsleri,
and
Fusarium oxysporum
by the incorporation of vermicompost into the growth media.
