Soil Renewal and Sustainability - Principles of Sustainable Soil Management in Agroecosystems - page 479

which would remove 10% to 30% of the gross estimated land from producing crops.
Fischer et al. (2002) cautioned that substantial expansion areas would have relatively
low productivity and would require extensive fertilizer applications to bring produc-
tion to acceptable levels. They further indicated that large areas of Asia not suitable
for rain-fed agriculture were being farmed at the time of the study, suggesting that
these areas will likely contribute relatively minor rain-fed production amounts in the
future. As much of this potential rain-fed agricultural area is in developing countries
in the lower latitudes, that is, in areas that have climate change predictions somewhat
unfavorable for agriculture (Intergovernmental Panel on Climate Change 2007),
agriculture production increases will not likely be proportional to the potential agri-
cultural expansion area. Expansion into areas with potential rain-fed productivity
holds some promise, but considering these areas as replacements for past and future
degraded land and for land taken out of production seems more than cautiously opti-
mistic, especially in considering the need to meet the rising global food, feed, and
fuel feedstock demand.
17.3 CLIMATE IMPLICATIONS
Climate change amplifies the food/feed production challenges previously identified.
When considered globally, the overwhelming evidence portrays future atmospheric
conditions leading to reduced potential for crop yields (Intergovernmental Panel on
Climate Change 2007). Recent studies further suggest that yields of major crops
have already been reduced significantly (Lobell et al. 2011); even more disconcert-
ing, research suggests that previous climate change crop yield reduction projections
may have been substantially too conservative (Lobell et al. 2012). That is, tempera-
ture extremes may reduce selected crop yields to a greater extent than models have
previously predicted.
The connection between changing climatic conditions and crop yield potential
has been made with at least one oversimplification—that soil quality remains static.
Because most agricultural soils have been degraded and will very likely continue
to degrade (FAO 2011), crop stress associated with less favorable soil conditions
coupled with a more variable climate must be included in crop modeling efforts if a
realistic picture of future crop production potential is to be obtained. Degraded soil
typically has lower rainfall infiltration rates, lower water holding capacity, lower
soil organic matter content, poorer drainage, and lower fertility than a comparable
soil in an undegraded condition. Not only must these conditions be considered, but
observed and predicted increased frequency of extreme rainfall events will esca-
late soil erosion pressures, aggravating existing degraded soil conditions found in
many locations (Soil and Water Conservation Society 2006; Nearing et al. 2004).
In fact, erosion rates are expected to increase disproportionately relative to rainfall
by a factor of about 1.7 (Nearing et al. 2004). The soil degradation drag on food
production, agricultural land conversion to other uses, limits to agricultural land
expansion, climate change-related production reductions, and accelerating demand
for agricultural products portray a food security system margin of error that continu-
ally narrows. Food security will rely increasingly on technological advances, that
is, advanced genetics, but technology's contribution to food, feed, fiber, and fuel