Agriculture Reference
In-Depth Information
>300%
(2%)
In 43% of cases,
increase was >20%
-100 to - 60%
(0.4%)
200 to 300%
(5%)
-60 to -20%
(4%)
100 to 200%
(9%)
-20 to 0%
(20%)
60 to 100%
(6%)
Region of
generally non-
significant
effects (with
little short-term
importance but
with possible
cumulative
importance)
20 to 60%
(21%)
0 to 20%
(33%)
In 75% of cases, earthworms
affected plant biomass positively
FIGURE 2.1
Effects of tropical earthworm species on plant shoot production. Each slice of the pie indicates
a range of shoot biomass increase due to earthworms (e.g., 0 to 20%), and the percentage of cases where that
range of increase was observed (values in parentheses). The chart was built using 246 data points (cases)
taken from a total of 28 experiments involving at least 34 earthworm and 19 plant species tested in 23 soil
types belonging to 8 great groups. (Modified from Brown et al., 1999.)
and various small
eudrilids all having a good potential for introduction and management into soils.
¤The earthworm biomass introduced or present in the soil, with higher yields usually
occurring in response to greater earthworm biomass in a curvilinear relationship (mod-
erate yield increases of 20 to 40% occurred with earthworm biomass values above 17 g
m
species
Drawida willsii
and West African species
Millsonia anomala
and over 40% of grain production increases occurred with earthworm biomasses
above 32 g m
−
2
).
−
2
¤
arthworm survival. In both pot and field trials, the mortality of introduced earthworms
was often high, particularly when the species was not adapted properly to the soil used
or when few or no organic residues were applied (survival was greater when organic
residues were present).
¤The presence of organic residues on the soil surface, with greater effects on plant yields
when such residues were present.
¤The timescale of the measurements (i.e., the duration of the experiment), usually with
positive cumulative increases in plant biomass because of earthworm activities with time,
although occasionally (depending on the soil type or earthworm and plant species) the
cumulative effects on plant biomass observed were negative.
Ε
he spatial scale of the experiment (i.e., pot vs. field experiments), with effects on yield
usually greater at the pot scale for any given plant and earthworm combination.
¤The natural richness of the soil used in the experiment, with greater benefits on produc-
tivity in poorer soils (low percentage carbon content, coarser textures) than in richer soils
(more carbon, clayey texture) with earthworms producing higher yields in moderately
acid soils (pH between 5.6 and 7.0) than in strongly acid soils (pH < 5.6) or alkaline
soils (pH > 7.0).
Different combinations of earthworm species, soil types and conditions, plant species, and
various imposed human or environmental constraints may alter the potential effects of the
earthworms on soil properties and plant growth. Thus, pinpointing the exact reasons for mechanisms
¤
Τ
