Agriculture Reference
In-Depth Information
EFFECTS OF EARTHWORM ON PLANTS: THE HISTORY
The importance of earthworms for soils, plant growth, and society has undergone various phases,
from profound recognition to utter ignorance and disdain. They were highly regarded as promoters
of soil fertility during the Egyptian empire (Minnich 1977), and early philosophers such as Aristotle
considered them beneficial animals, calling them the ÑearthÔs entrailsÒ (or intestines) (Kevan 1985).
From antiquity to DarwinÔs time, however, not much information is available on earthworms (see
review by
Kevan
1985); throughout much of the 17th up to the beginning of the 20th century,
earthworms were considered garden pests that needed elimination from soils (Minnich 1977; Brown
et al. 2004).
Probably the earliest and best-known report of the potential benefits of earthworms to soils is
the much-quoted letter of Rev. Gilbert White to the Hon. Daines Barrington, written on May 20,
1777. This letter also provided some first hints of the mechanisms by which earthworms affect
plant growth. White (1789) wrote:
Dear Sir Ð
Earthworms, though in appearance a small and despicable link in the chain of Nature,
yet, if lost, would make a lamentable chasm. For to say nothing of half the birds, and some quadrupeds
which are almost entirely supported by them, worms seem to be the great promoters of vegetation,
which would proceed but lamely without them, by boring, perforating, and loosening the soil, and
rendering it pervious to rains and the fibers of plants, by drawing straws and stalks of leaves and twigs
into it; and most of all, by throwing up such infinite numbers of lumps of earth called worm-casts,
which, being their excrement, is a fine manure for grain and grass
T
Gardeners and farmers express
their detestation of worms; the former because they render their walks unsightly, and make them much
work; and the latter because, as they think, worms eat their green corn. But these men would find that
the earth without worms would soon become cold, hard-bound, and void of fermentation, and conse-
quently sterile; and, besides, in favour of worms, it should be hinted that green corn, plants, and flowers,
are not so much injured by them as by many species of
T
(long-legs)
in their larva, or grub-state; and by unnoticed myriads of small and shell-less snails, called slugs, which
silently and imperceptibly make amazing havoc in the field and garden.
coleoptera
(scarabs), and
Tipulidae
It was not until almost a century later that Darwin (1881), in his book
The Formation of Vegetable
Mold Through the Action of Worms
, firmly established the benefits of earthworms to soils. Other
authors (Hensen 1877, 1882; Mller 1878, 1884; Wollny 1890) supported the positive role of
earthworms in soil processes and plant growth, and Wollny (1890) was the first actually to quantify
this relationship. Despite initial skepticism about the reports of Darwin and Hensen (Wollny 1882a),
he became convinced that earthworms were important for plant production when his experiment
showed increased yields of 12 species of plants, ranging from negligible amounts up to 733%
(rape), by adding earthworms (Wollny 1890). However, he continued to warn about the generali-
zation of these results to field situations.
From the early 20th century to the present, the number of experiments increased, and the
intervals between them decreased, so that there are presently more than 120 papers published on
the effects of earthworms on plant production. The aim of most of these investigations was to
answer the following questions:
¤Do earthworms affect plant growth (positively or negatively), and if so, by how much?
¤Which plants are affected most (positively or negatively)?
¤Which earthworm species are most efficient at promoting plant growth?
