Agriculture Reference
In-Depth Information
of corn and soybean residues than without grazing under conventional tillage (1.34
vs. 1.17 Mg m
−3
), but not under no till (1.27 vs. 1.25 Mg m
−3
) (Diaz-Zorita et al. 2002).
Pastures and forage cropping systems can result in higher bulk density than con-
ventional cropping systems, because of heavy traffic combined with general lack of
tillage, but can also result in lower bulk density due to SOC accumulation, vigorous
rooting, and soil faunal activity. In the southeastern United States, soil bulk density
at a depth of 0-20 cm was 1.48 Mg m
−3
under a 20-year-old tall fescue-common
Bermuda grass pasture and 1.57 Mg m
−3
under a 24-year-old conservation-tillage
cropland (Franzluebbers et al. 2000b). In western Canada, soil bulk density at a
depth of 0-10 cm was not different among forage and no-till cropping systems man-
aged continuously for 10 years (Arshad et al. 2004).
Taking all of the results on bulk density into consideration, animal grazing gener-
ally compacts soil; however, the extent of this compaction may be mitigated by con-
trolling the timing and extent of grazing and whether the soil surface is firm enough
to withstand the traffic.
4.2.4 r
unoff
and
S
oIl
e
roSIon
The loss of nutrient-rich topsoil by erosion can degrade many soil properties, includ-
ing bulk density, available water-holding capacity, soil pH, and cation exchange
capacity, thereby lowering crop productivity even with high fertilizer additions
(Gantzer and McCarty 1987; Bauer and Black 1994). During overland flow, litter
can increase surface hydraulic roughness and produce deeper overland flow to allow
longer duration for infiltration (Ellis et al. 2006). Paudel et al. (2009) reported that
about two-thirds of the land in the Nepal Himalaya ecosystem is degraded and that
soil erosion could be as high as 87 Mg ha
−1
year
−1
on a sloping terrace. High human
population density leading to cultivation of marginal lands, livestock grazing, and
depletion of biomass cover are accelerating land degradation with associated prob-
lems of malnutrition, out migration, and biodiversity loss. Soil conservation in the
Inner Mongolia Autonomous Region is required to protect the soil resource base to
meet nutritional requirements of the population and reduce the health risks to people
and livestock associated with dust storms (Lafond et al. 2009). Appropriate conser-
vation tillage practices were identified for small farms in the region without large
requirements for capital and the need to incur a lot of risk. The authors recommend
education and training programs focusing not only on farmers but also on custom
machinery operators and crop input suppliers.
Ritchie et al. (2009) found that shrub-dominated subwatersheds contributed most
of the suspended sediment that was measured at the outlet flume of the Walnut Gulch
Experimental Watershed in southern Arizona, United States. These subwatersheds
delivered more suspended sediment to the stream systems than grass-dominated
landscapes. They recommended management techniques to protect grass-dominated
areas from shrub invasion. In a karst topographic region, Stamati et al. (2011) found
that soils devegetated by grazing had lower SOC and nitrogen contents and lower
biological activity than naturally vegetated soils. Furthermore, they found a linear
relationship between dissolved nitrogen export from a watershed and livestock graz-
ing intensity.
