Agriculture Reference
In-Depth Information
decomposers can colonize. Decomposers or microorganisms are much
smaller and consist of Archaea, bacteria, fungi, actinomycetes, algae,
nematodes, and protozoa, which collectively have an extraordinary range
of ability in decomposing organic compounds, as well as exhibiting
complex predator-prey relationships.
4. Reducers and decomposers together comprise the soil biomass,
amounting to as much as 2000 to 4000 kg “live weight” per hectare. The
decomposers are referred to as the soil microbial biomass (SMB), which
ranges in size from 100 to 1000 mg C/kg to 15-cm depth.
5. Measures of soil organic carbon (SOC) and SMB can be used to assess
a soil's biological health. The benchmark for SOC (%C) ranges from
>0.5 for a sand to >2 for a clay soil. The benchmark for SMB by the
chloroform fumigation-extraction method is >150 to 400+ mg C/kg to
15-cm depth.
6. The food or substrate supply is the main factor controlling the size of the
soil biomass. Microorganisms flourish in the rhizosphere because of the
availability of C substrates from roots. Although drastic changes such as
air-drying or freezing a soil kill many organisms, the survivors multiply
rapidly when favorable conditions are restored because they have less
competition. Microorganisms can also adapt to decomposing unusual
substrates added to soil, such as organic pesticides, because in doing so
they have a competitive advantage over non-adapted organisms.
7. A thriving and diverse biomass is the key to a properly functioning
soil ecosystem, with benefits to plants possible from growth-regulating
compounds produced by specific organisms. The mycorrhizal
symbiosis between a fungus and grapevine roots improves P uptake.
The legume-
Rhizobium
symbiosis “fixes” atmospheric N
2
in plants
such as clovers, beans, peas, and medics that are sown in cover crops,
providing N benefits to the vines.
8. Healthy soil microflora and fauna are achieved by maintaining an
adequate input of organic materials through cover crops, mulches,
manures, and compost. Mulches are usually organic materials that do
not decompose readily, such as straw, wood chips, or biochar. A mulch
moderates diurnal soil temperature fluctuations, reduces soil evaporation,
and encourages earthworms.
9. Composting involves the predecomposition of organic residues, often
with manure added, to reduce the C-to-N ratio. Compost is used
in conventional and organic viticulture to provide nutrients and, if
sufficient quantities are applied for a number of years, SOM can be
increased.
