Agriculture Reference
In-Depth Information
vermicomposts produced from animal wastes tend to be on the alkaline side of neutral (pH
>7.0), whereas most plants prefer a growth medium slightly on the acid side of neutral (e.g.,
with a pH of 6.0). The processing of organic wastes by earthworms does not change the pH of
the material appreciably, so earthworm-worked wastes benefit from some acidification or from
mixing with an acid medium such as peat.
G
ROWTH
OF
P
LANTS
IN
V
ERMICOMPOSTS
There is very well-substantiated evidence that vermicomposts can promote the growth of plants
significantly. For instance, Fosgate and Babb (1972) grew earthworms in cattle wastes and reported
that the vermicomposts produced were equal to greenhouse potting mixes for production of flow-
ering plants. Reddy (1988) reported increased growth of
Vinca rosea
and
Oryza sativa
after addition
of cast material from
Pheretima alexandri
to soils
.
Buchanan et al. (1988) suggested that most
vermicomposts had more available nutrients than the organic wastes from which they were pro-
cessed. Edwards (1988) reported that most samples of vermicomposts had relatively high levels of
available nitrogen. Handreck (1986) reviewed the utilization of vermicomposts as horticultural
potting media and concluded that, although they could supply most of the trace element needs of
plants, many vermicomposts may not have sufficient nitrogen to supply all the needs of the plants.
However, it seems difficult to justify this conclusion because most organic wastes have excess
amounts of nutrients, and usually only a small proportion of these is lost during efficient and rapid
vermicomposting (Edwards et al. 1985). It seems probable that the vermicomposts that Handreck
tested had been produced very slowly and had lost most of their nutrients through either volatil-
ization or leaching.
In extensive greenhouse trials testing the growth of a wide range of plants in a variety of
earthworm-worked wastes (Edwards and Burrows 1988), most plants germinated earlier and grew
better in vermicomposts than in commercial plant growth media. A wide range of plants were
grown successfully in both undiluted worm-worked wastes as well as in a range of dilutions and
mixes with bulking materials, including 3:1 or 1:1 ratios of earthworm-worked organic wastes to
peat, pine bark, or a Kettering loam soil.
Plants that were tested for their rates of growth in vermicomposts by Edwards and Burrows
(1988) included vegetables such as aubergines (eggplant), cabbages, peppers, cucumbers, lettuces,
radishes, and tomatoes; bedding plants such as
Alyssum, Antirrhinum, Aster, Campanula. Cal-
ceolaria, Cineraria, Coleus,
French marigold, plumose asparagus, sweet peas,
Polyanthus,
and
Salvia
(Edwards and Burrows 1988); and ornamental shrubs such as
Eleagnus pungens, Cotoneaster
conspicua, Pyracantha
sp.:
Viburnum bodnantense, Chaemaecyparis lavisonia, and Juniperus com-
munis
(Scott 1988).
After processing, vermicomposts usually have about 75% moisture content and may need some
drying before use. If the waste is likely to contain human pathogens or weed seeds, a brief
thermophilic precomposting for 3 to 4 days may be advisable as a precaution. Usually, a magnesium
sulfate supplement is necessary to rectify magnesium deficiencies that may occur in many animal
wastes, and the pH can be adjusted in some way, such as by adding acid peat, to bring the medium
to a pH of about 6.0. Such vermicomposts seemed to accelerate the germination and subsequent
growth and yields of seedlings of most species of plants tested. A wide range of tests of seedling
emergence of pea, lettuce, wheat, cabbage, tomato, and radish were made in small pots and trays
using the standard European Economic Community recommended seedling-emergence test. The
germination of tomatoes, cabbage, and radish seedlings tended to be significantly better in vermi-
composts than in commercial plant growth media and much better than in composted animal wastes
with no earthworms. Similarly, the early growth of seedlings of ornamentals up to the stage when
they were transplanted into larger pots or outdoors was better in the animal waste vermicomposts
mixed with peat than in a commercial plant growth medium.
