Agriculture Reference
In-Depth Information
and life-form composition and cover, but spatial variation was considerable; (iv) soil
characteristics, climate, and disturbances may have a greater effect on plant species
diversity than the studied levels of grazing; and (v) few plant species showed consis-
tent, directional responses to grazing or cessation of grazing.
In communally grazed rangeland in South Africa, Moussa et al. (2007) showed
no significant differences in SOC and soil microbial biomass between grazed and
ungrazed plots at any of the sites. In diverse degraded landscapes, soil characteris-
tics were enhanced in grazing exclosures compared with grazed pasture, such as in
an active sand dune area (Li et al. 2012) in a desertified region (Chen et al. 2012),
in degraded land in Ethiopia (Girmay and Singh 2012), and in fescue paddocks in
Canada (Dormaar and Willms 1998). In moderately grazed and fertilized pastures,
soil characteristics were better in grazed pasture than in exclosure areas (Manley et
al. 1995; Wienhold et al. 2001). Stohlgren et al. (1999) found no significant differ-
ences in species diversity, evenness, cover of various life forms (grasses, forbs, and
shrubs), soil texture, or soil percentage of nitrogen and SOC between grazed and
ungrazed sites in Rocky Mountain grasslands. Dormaar et al. (1997) reported that
grazing mixed prairie at a low stocking rate had no effect on the vegetation but did
alter soil quality.
4.3.2 p
aSture
S
yStemS
Rotational or management-intensive grazing has increasingly received attention as
a potential strategy to rejuvenate degraded pastures, increase productivity, increase
profit, and possibly sequester SOC and improve soil quality (Beetz and Rinehart
2010). There are too few research data to fully support claims for greater SOC and
improved soil quality with these practices; however, there are some positive results
reported. From a field survey of eight pastures in Virginia, Conant et al. (2003)
reported 8.2 ± 4.5 Mg ha
−1
greater SOC under pastures with management-intensive
grazing than with extensive grazing. This equated to an SOC sequestration rate of
0.61 Mg ha
−1
year
−1
during an evaluation period of 14 ± 11 years. In a survey of pas-
tures in three counties in northern Texas, SOC was greater with rotational than with
continuous grazing (Teague et al. 2011). At the end of 4 years of differential graz-
ing method in New South Wales Australia, microarthropod abundance was greater
with high-intensity/short-duration grazing than with set stocking (Tom et al. 2006).
However, no differences were found in bulk density, earthworm abundance, soil
microbial biomass, and respiration.
4.3.3 c
rop
-l
IveStock
S
yStemS
Integrated crop-livestock systems are usually designed to capture ecological syner-
gies between (i) high cultural requirements and productivity of crops but system
susceptibility for nutrient losses, and (ii) relatively low input requirements of animal
grazing systems but large potential for utilizing low-value crop residues or cover
crops and absorbing nutrients and spreading risk (NRC 2010; Franzluebbers et al.
2011). Some examples of such systems are described to illustrate the impacts of
direct grazing on production and environmental quality responses.
