Agriculture Reference
In-Depth Information
and Rose, 1991; Uusitalo et al., 2001; Zhang et al., 2003a). Despite the current use of soil and water
conservation practices, losses of sediment, N, and P from rural lands remain high (USEPA, 1996).
Annual sediment loss in the United States exceeds 10 billion metric tons and costs the society 44
billion US$ of degraded water resources (USEPA, 1996; Blanco-Canqui et al., 2004). Similarly,
heavy metals also contaminate vast land areas. Heavy metal inputs included those from commer-
cial fertilizers, liming materials and agrochemicals, sewage sludges, and other wastes used as soil
amendments, irrigation waters, and atmospheric deposition (Senesi et al., 1999; He et al., 2004).
Soils receiving repeated applications of organic manures, fungicides, and pesticides have exhibited
high concentrations of extractable heavy metals (Sims and Wolf, 1994; Han et al., 2000) and sub-
sequently resulted in increased heavy metal concentrations in the runoff (Moore et al., 1998). The
mobility of heavy metals depends not only on the total concentration in the soil but also on soil
properties, metal properties, and environmental factors (He et al., 2004). Dowdy and Volk (1983)
reported that the movement of heavy metals in soils could occur in sandy, acidic, and low OM soil
subject to heavy rainfall or irrigation.
Yamaguchi et al. (2004) reported that HA is a representative ligand that controls the mobility
and fate of metal species in soils and aquatic systems. Li et al. (2003) reported that the amphipathic
nature of HAs enables them to interact with a wide variety of inorganic and organic pollutants,
including heavy metals and charged organic pollutants via chemical bonding and less polar organic
pollutants through nonspecific physical interactions. Owing to their ubiquity in surface aquatic and
groundwater systems, HAs often play important roles in environmental processes governing the
fate and transport of organic and inorganic pollutants in soil-plant systems (Weber, 1988; Bartschat
et al., 1992; Stevenson, 1994; Li et al., 2003). OM increases the CEC of soils, which may be respon-
sible for reducing the leaching of essential plant nutrients and heavy metals in the soil profile. In
addition, OM constituents carry a negative charge and are hence able to adsorb heavy metal cations
(Mengel et al., 2001).
4.9.2 r
eduCtIon
In
s
oIl
e
rosIon
Soil erosion has been defined as the process of detachment and transportation of soil material by
erosive agents (Ellison, 1947). Soil detachment is the subprocess of dislodgment of soil particles
from the soil mass at a particular location on the soil surface (Zhang et al., 2003b). Soil erosion
by wind and water is a worldwide concern in reducing soil quality, maintaining farming systems
sustainability, and increasing environmental pollution (Fageria, 2002). Soil aggregates low in OM
and clay contents are generally susceptible to disintegration at low rainfall energies and subject to
erosion (Rhoton et al., 2003). Several million hectares of soils in the United States are subject to
excessive runoff and erosion losses because of the low levels of OM and clay content (Rhoton and
Tayler, 1990; Rhoton et al., 2003). Soil erosion from irrigation, especially furrow irrigation, con-
tributes to nonpoint-source pollution (Lentz et al., 1996) and is a serious threat to crop productivity
in many regions (Carter, 1993).
Accelerated soil erosion also removes the layer of topsoil that is richest in OM (Hillel and
Rosenzweig, 2002). Bauer and Black (1994) reported that soil erosion in the northern Great Plains
of the United States is deemed to diminish soil productivity through the concomitant diminution
of SOM content. Bauer and Black (1994) reported that loss of soil productivity resulting from a
decline in SOM content associated with soil loss by erosion in the northern Great Plains of the
United States is a consequence of the concomitant loss of fertility. Carpenter et al. (1998) reported
that P is primarily transported through surface runoff from agricultural lands and was a major cause
of eutrophication in surface waters. Pennock and Van Kessel (1997) assessed soil redistribution in
landscapes of southern Saskatchewan with different cultivation histories and showed that SOM was
the major soil quality indicator influenced by erosion. Gregorich et al. (1998) reviewed the relation
between soil erosion and deposition processes and distribution and loss of SOM using the century
model.
