Agriculture Reference
In-Depth Information
FOOD
CONTROL
GRASS CLIPPINGS
+
Wei
Mat
+
Gwt
+
GROWTH (PC1)
PINE NEEDLES
PAPER
+
Coc
SAWDUST
CARDBOARD
REPRODUCTION (PC2)
FIGURE 20.2
Effect of different diet treatments in the plan defined by factorial axes representing growth
and reproduction of the earthworm
Eisenia andrei
. Mat, sexual maturity; Wei, earthworm weight; Gwt,
earthworm growth; Coc, cocoon production; PC1 represents 46.5% of total inertia, and PC2 represents 36.87%.
active. Transformations of the organic wastes after 2 months during this effective vermicom-
posting period are summarized in
Figure 20.3
.
P
H
DURING
V
ERMICOMPOSTING
The pH of the pig slurry used in our vermicomposting experiments ranged from 8.2 to 8.7. The
vermicompost obtained after 2 months was slightly acidic, with similar pH values to the parent
waste without earthworms (control), proving that earthworms did not affect the pH values to any
great extent (Figure 20.3A). The effects of earthworms on pH of wastes during vermicomposting
is probably related to increases in the mineral nitrogen content of the substrates, changes in the
ammonium-nitrate equilibrium, and accumulation of organic acids from microbial metabolism or
from the production of fulvic and humic acids during decomposition.
C
ARBON
M
INERALIZATION
DURING
V
ERMICOMPOSTING
Similar to other invertebrates in the organic matter decomposer community, earthworms can assim-
ilate carbon best from the more recently deposited organic matter fractions, consisting mainly of
easily degradable substances. The degradation process resulted in carbon losses by mineralization,
which produced a decrease in the amounts of total organic carbon and in the carbon contributions
to the organic matter (Figure 20.3B). Although earthworms consume and process large amounts of
organic matter, their contributions to the total heterotrophic respiration is quite low because of their
poor assimilation efficiency; only when there are large active earthworm populations, as in vermi-
composting systems, can they contribute appreciably to the total heterotrophic respiration.
N
ITROGEN
T
RANSFORMATIONS
DURING
V
ERMICOMPOSTING
Earthworms had a great impact on the nitrogen transformations in the pig manure by enhancing
nitrogen mineralization, so that most mineral nitrogen was retained as nitrates. The net total nitrogen
and the different nitrogen fractions decreased during vermicomposting, and important reductions
in organic nitrogen content and a high nitrification rate were noted (Figure 20.3C). This implies
