Agriculture Reference
In-Depth Information
feedstock production will be met only if the soil in which crops grow can supply the
required (and timely) quantities of water and nutrients. Continued degradation of
soils will limit technology's contribution to global food security.
17.4 AGRICULTURE AND SOIL EROSION
Humans have altered the relationship between soils, climate, and plants. Through
agriculture, we have replaced native species, in most situations, with species that are
not as well adapted to a specific location, but that yield products favorable for human
consumption or human use. As would be expected, the most productive soils (those
with relatively high native fertility and favorable physical condition), Mollisols and
Alfisols, account for a major portion of farmed soils globally (Eswaran et al. 2012).
That is, rain-fed agriculture is practiced in areas of the world having a combination
of climate and parent material properties that historically favored relatively high
amounts of plant growth. In part, because crops selected for agricultural produc-
tion normally are not the most naturally productive/competitive species for the soil
and climate combination where farming is practiced, humans manipulate soil physi-
cal and chemical properties through practices such as tillage and/or fertilization to
enhance production of their chosen crop. In doing so, the soil is often exposed to rain
and wind and left vulnerable to soil erosion, which removes the upper layer(s) of soil
material. The physical and chemical soil environment is changed; usually, plant root-
ing is shifted downward into less weathered materials lower in both organic matter
and fertility and with poorer soil physical conditions.
Accelerated soil erosion is a degradation process; however, concurrently, soil
physical and chemical changes occur, producing new soil from parent material. Soil
renewal, or development, involves physical, chemical, mineralogical, and biological
processes. In reality, the net soil change at a given location on the landscape is the
combined effect of soil detachment, transport, and deposition through erosion and
soil addition through soil development.
17.5 SOIL DEVELOPMENT AND AGRICULTURE
Plant biochemistry associated with growth and food production (seed, fruit, and
tubers) relies on chemical elements (nutrients) and water obtained from the soil.
Without these materials, selected required plant chemical processes are limited or
do not occur, plant productivity decreases, and in worst-case scenarios, the plant
simply cannot survive. Further, plants must obtain quantities of these elements in
proportion to their needs, that is, elements have a very limited capacity to substitute
one element for another in basic plant physiological processes. If one element is
limiting, even when others are in adequate supply, plant function is disrupted. Also,
and equally important, different plants require different amounts of the necessary
elements for survival and maximum production. Certain soil conditions are better
suited for certain plants.
The amount and proportion of the different plant-required elements vary spatially
and are related to the chemical and mineral characteristics of the parent material.
These factors also vary vertically in the soil profile depending on a variety of factors,
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