Agriculture Reference
In-Depth Information
Table 5.4
Earthworm Biomass under Different Management Practices in a
Barossa Valley Vineyard
Management practice
Earthworm biomass (kg live weight/ha)
Mulch of grape marc
220
Ryegrass cover crop, slashed and thrown
under the vines
300
Bare soil, surface application of lime
340
Straw mulch
450
Straw mulch plus lime
700
From White (2003); original data from Buckerfield and Webster (2001).
are important for the pollination of plants used as cover crops. Centipedes are
fast-moving, carnivorous arthropods, feeding on insects and other small animals,
whereas millipedes are slow-moving plant-feeders, mostly saprophytic. Some,
however, feed on living roots, bulbs, and tubers and therefore can be pests.
Molluscs
Many molluscs (slugs and snails) feed on living plants and are therefore pests.
Some species feed on fungi and the feces of other animals. Because the mollusc
biomass is only 200 to 300 kg/ha in most soils, slugs and snails make only a lim-
ited contribution to the decomposition of organic matter.
Protozoa and Nematodes
Protozoa and nematodes (roundworms) are important because they control the
size and composition of the bacterial and fungal populations and in so doing
influence the rate of nutrient turnover. Protozoa live exclusively in water films in
very small pores. Next to the protozoa, the threadlike nematodes are the smallest
of the soil fauna, ranging from 0.5 to 2 mm in length. Nematodes can num-
ber up to 10 million/m
2
, mainly in the litter layer and topsoil, where they feed
on fungi, bacteria, protozoa, and other nematodes. Root knot and root lesion
nematodes are serious parasites of grapevine roots (see “Nematodes and Their
Control,” this chapter).
Changes in Soil Organic Matter
How Is Soil Organic Matter Depleted?
When humans cultivate soil to grow crops, the C cycle is disturbed. Generally,
in cultivated soil the C released as CO
2
, plus that removed in harvested products
and lost by erosion and leaching, exceeds the input from photosynthesis and the
