Agriculture Reference
In-Depth Information
Earthworm Biomass Under Different Management Practices
in a Barossa Valley Vineyard
Table 2.4
Earthworm Biomass
(kg/ha)
Management Practice
Mulch of grape marc (pomace)
Ryegrass cover crop, slashed and thrown
into the rows
Bare soil, surface application of lime
Straw mulch
Straw mulch plus lime
220
300
340
450
700
Source:
Data from Buckerfield and Webster (2001)
for the earthworms, conserves soil moisture, and reduces surface soil temperatures.
When combined with lime to raise the soil pH, straw mulch encouraged the high-
est earthworm biomass.
Nematodes and molluscs
. Next to protozoa, the threadlike
nematodes
are among
the smallest of the soil fauna, ranging from less than 1 mm to a few mm in size.
They are plentiful in soil and litter and may feed on dead organic matter or liv-
ing fungi, bacteria, or other nematodes. Root-knot and root-lesion nematodes can
be serious parasites of grapevine roots (section 7.3.3.2).
Other quite primitive soil animals are the
molluscs
(slugs and snails), many of
which feed on living plants and are therefore pests. Some species feed on fungi
and the feces of other animals. Because their biomass is only 200-300 kg/ha in
most soils, the contribution of molluscs to the decomposition of organic matter
is limited.
Measuring the Soil Biomass
The biomass of the large and small soil animals is easy to measure by direct meth-
ods in which they are isolated from the soil, counted, and weighed. This is not
the case with the microorganisms, which are intimately mixed with the
SOM
and,
being very small, are difficult to isolate and count or weigh. Methods for mea-
suring the microorganisms collectively—the soil
microbial biomass
—are discussed
in appendix 2. Estimates of microbial biomass C range from 500-2,000 kg/ha to
15-cm depth. Biomass C is only a small fraction of the total soil C, from about
1-2% in arable soils to 2-3% in grassland soils.
2.3.2.3
Decomposition and Formation of Humus
Humification
is the process by which identifiable plant parts are physically and
chemically altered to a black, amorphous material called
humus
. During humifi-
cation, plant carbohydrates and proteins are decomposed and their microbial ana-
logues are synthesized. Polymerization reactions involving aromatic compounds
(unsaturated ring structures of C and H, of which the simplest is benzene C
6
H
6
)
also occur. For example, simple hydroxy-phenols occurring naturally in plants, or
produced from the breakdown of lignin and polyphenolic pigments, are oxida-
tively polymerized to form humic precursors. Nitrogen is incorporated into the
polymers if amino acids combine with the phenols before polymerization. An im-
2.3.3
