Agricultural-Based Food Production Geoenvironment Stressors - Sustainable Practices in Geoenvironmental Engineering - page 181

6.3 Stressor Impacts on Water and Soil
Two of the most important ingredients in agricultural-based food production, other than
climatic conditions, are water and soil —more speciically, adequate water supply and soil
q u a l it y.
6.3.1 Water Utilization
The availability and quality of water are two important water factors that impact signii-
cantly on the health and welfare of a growing population, particularly in developing coun-
tries. Freshwater is a precious resource because of the limited amounts directly available
for use. More than half of runoff water is used by humans, and 70% of this is for agricul-
ture (Postel et al., 1996). Rivers are diverted to serve the needs of humans. Only 2% of the
rivers in the United States have not been manipulated. As an example of the impact of
excessive use of water for agricultural purposes, it is reported that the water levels of the
Aral Sea, located in Central Asia in the lowlands of Turan, have been substantially reduced
by agricultural practices. The result of this has been (a) loss of native ish and biota, (b) cre-
ation of a source of windblown dust from the exposed salty sea bottom, (c) increase in the
frequency of human diseases, and (d) creation of a drier local climate (Micklin, 1988).
The cost of energy inluences one's ability to extract, pump, and irrigate abstracted
groundwater. Increasing agricultural yields coupled with increasing land for agriculture
result in corresponding increases in water demand. About 33% of the world's food is pro-
duced by irrigation (Postel, 1992). Management for salinity and drainage is required to
avoid decreases in agricultural yields. Falling water tables increase the costs of abstraction
of groundwater—a factor that needs to be incorporated into management of irrigation.
Irrigation involves exploitation of rivers, aquifers, or other freshwater sources, causing a
disruption of the natural hydrological cycle. If irrigation is poorly controlled, desiccation
can occur between watering periods. This can lead to increasing rates of aridiication and
wind erosion. Over-irrigation can deplete freshwater sources, and the soil can become
salinated due to increased evaporation at the surface horizons. Substantial amounts of
water are required for production of various crops. As shown in Figure 6.2, the growing of
corn, rice, and soybeans require substantially more water than wheat. Livestock requires
100 times more water than 1 kg of vegetable protein. Overall, in 2005, less than 1% of the
total amount of water was used to raise livestock (Kenny et al., 2009). It has been estimated
that up to 20,000 L of water are required to produce 1 kg of beef on a range, approximately
100 times the amount to produce 1 kg of tomatoes (214 L/kg) (Institution of Mechanical
Engineers [IME], 2013). Increase in livestock and crop production required to satisfy the
needs of a growing population will continue to stress water resources (Giampietro and
Pimentel, 1995)—in addition to extensive food wastage (30% to 50% of all food produced)
due to inadequate harvesting, storage, and transportation procedures (IME, 2013).
Mining of groundwater is necessary because of demand for freshwater by the increasing
population and subsequent use of irrigated agricultural practices (Falkenmark, 1989). Up
to 68% of the groundwater withdrawn in the United States is for agriculture (USGS, 2014).
Water tables have fallen at the rates of 3 to 120 cm/year in the United States in some areas
(Sloggett and Dickason, 1986), and in China, at rates of 1 to 2 m/year (Postel, 1992). Some
groundwaters cannot reach the ocean in the dry season.
Conlicts over water use due to irrigation have occurred in various parts of the world. The
Egyptians have used the Nile for more than 5000 years while the other nations in the upper