Agriculture Reference
In-Depth Information
Depending on the location, there is a small input of N from the atmosphere
(see “Nitrogen Cycling,” chapter 3) and a variable amount from legume N
2
fixa-
tion (see box 5.2, chapter 5). Overall, however, nutrient export and loss will not
be matched by inputs of nutrients from the air, nor by the vines “mining” weath-
ering rock in the subsoil. Thus an external input of nutrients is needed for an
organic vineyard to be biophysically sustainable, which means that some other
part of the biosphere is depleted of nutrients (and hence set to become unsustain-
able). Furthermore, if an organic vineyard is truly maintained as a closed system,
the inevitable depletion of nutrients over a long period will result in unthrifty
vines and poor yields, making the enterprise financially nonviable and therefore
unsustainable.
Although recycling C and nutrients through the return of vine residues and
composted materials is to be encouraged where possible, it needs to be done in
conjunction with a calculation of a vineyard's nutrient budget, as well as soil and
plant testing to assess the vines' nutrient status. Furthermore, we should note that
the operating costs of organic vineyards are generally higher than for conventional
vineyards. Organic winegrowers in Australia at least are not paid a premium for
their fruit by wineries, nor is there a consistent premium in the marketplace for
organic/biodynamic wines.
Climate Change and Possible Consequences
Figure 6.9A shows that since reliable records began in 1850, according to the
11-year moving average, the mean global surface temperature has increased by
about 0.8
o
C. The temperature trend for Australia, from 1910 to the present, is
broadly similar but shows much greater interannual variability (figure 6.9B—
note the differences in the scales of the
x
and
y
axes). Both graphs show an approxi-
mately linear increase in mean temperature for the last 50 years of the 20th century
(up to 1999), with the increase for the planet being about 0.6
o
C.
The Intergovernmental Panel on Climate Change (2007) stated in its
Fourth Assessment Report that the observed temperature increase (such as fig-
ure 6.9A) could be simulated only by models that incorporated anthropogenic
forcing (from GHG) and not natural factors alone. The Fifth Assessment Report
(IPCC, 2013) confirmed with very high confidence that this conclusion was
true. Nevertheless, projection of model outputs beyond the range of measure-
ments always introduces uncertainty not only because of an incomplete under-
standing of the complex interactions that influence the earth's climate but also
because of assumptions made about future “emission scenarios” (Pittock, 2005),
or Representative Concentration Pathways, as they are now called. As discussed
in “Climate” in chapter 2, the actual temperature increase from 1970 to 2009
is tracking at the lower level of the ensemble average of model projections.
Furthermore, although GHG emissions have continued to increase from 2000
