Impacts of Climate Change on Agriculture - Climate Resilient Agriculture for Ensuring Food Security - page 65

increased proneness to wind erosion. Susceptibility
to wind erosion depends in part on cohesiveness of
the soil (which is affected by precipitation effec-
tiveness) and wind velocity. The only study com-
pleted on this subject suggests that in Saskatchewan
(on the Canadian prairies) the frequency of moder-
ate and extreme droughts would increase threefold
under a 2xCO 2 climate if mean May-August tem-
peratures increased by 3.5 °C and precipitation
increased by 9-14 %, which is consistent with the
GISS 2xCO 2 climate. They would increase 13-fold
if increases in temperature are not accompanied by
increases in precipitation.
Soil temperature affects the rates of organic
matter decomposition and release of nutrients.
At high temperatures, though nutrient availability
will increase in the short term, in the long run
organic matter content will diminish, resulting in a
decline in soil fertility. Estimated changes in the
potential for wind erosion under the latter scenario
vary from +24 to +29 % (Williams et al. 1988 ).

4.5 Soil Fertility and Erosion

The soil system responds to short-term events
such as rainfall and also undergoes long-term
changes such as physical and chemical weather-
ing due to climate change. The potential impacts
on soil health due to climate change would be in
the organic matter supply, temperature regimes,
hydrology, and salinity. Soil carbon levels are
expected to decrease due to decreased net pri-
mary production. Any gains by the increased
plant water-use effi ciency, due to elevated CO 2 ,
are likely to be outweighed by increased carbon
mineralization after episodic rainfall and reduced
annual and growing season rainfall. The quality
of soil organic matter may also shift where the
more inert components of the carbon pool pre-
vail. The increase in soil temperature increases N
mineralization, but its availability may decrease
due to increased gaseous losses through pro-
cesses such as volatilization and denitrifi cation.
No comprehensive study has yet been made of
the impact of possible climatic changes on soils.
Higher temperatures could increase the rate of
microbial decomposition of organic matter,
adversely affecting soil fertility in the long run
(Hillel and Rosenzweig 1989 ). But increases in
root biomass resulting from higher rates of pho-
tosynthesis could offset these effects. Higher
temperatures could accelerate the cycling of
nutrients in the soil, and more rapid root forma-
tion could promote more nitrogen fi xation. But
these benefi ts could be minor compared to the
deleterious effects of changes in rainfall. For
example, increased rainfall in regions that are
already moist could lead to increased leaching of
minerals, especially nitrates. In the Leningrad
region of the USSR, a one-third increase in rain-
fall (which is consistent with the GISS 2xCO 2
scenario) is estimated to lead to falls in soil pro-
ductivity of more than 20 %. Large increases in
fertilizer applications would be necessary to
restore productivity levels (Pitovranov et al.
1988 ).
Decreases in rainfall, particularly during sum-
mer, could have a more dramatic effect, through
the increased frequency of dry spells, leading to

4.5.1 Soils

Climate change will also have an impact on the
soil, a vital element in agricultural ecosystems.
Higher air temperatures will cause higher soil
temperatures, which should generally increase
chemical solution reaction rates and diffusion-
controlled reactions (Buol et al. 1990 ).
Solubilities of solid and gaseous components
may either increase or decrease, but the conse-
quences of these changes may take many years to
become signifi cant (Buol et al. 1990 ).
Furthermore, higher temperatures will accelerate
the decay of soil organic matter, resulting in
release of CO 2 to the atmosphere and decrease in
carbon/nitrogen ratios, although these two effects
should be offset somewhat by the greater root
biomass and crop residues resulting from plant
responses to higher CO 2 .
In temperate countries where crops are already
heavily fertilized, there will probably be no major
changes in fertilization practices, but alterations
in timing and method (e.g., careful adjustment of
side-dress applications of nitrogen during vegeta-
tive crop growth) are expected with changes in