Grasslands of the World.pdf - Disasters and Conflicts - UNEP

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Grasslands of the world
of a few days or even, in extreme cases, hours, since all the livestock normally
allocated to the entire area are concentrated into one paddock at a time.
Savory has stated that stocking could be doubled over that recommended by
standard Soil Conservation Service procedures (Bryant et al., 1989). Results of
experiments involving short-duration grazing in the Great Plains have been
mixed . Holechek, Pieper and Herbel (2001) evaluated nine studies conducted
on USA and Canadian grasslands. Many of these studies showed little difference
in herbage yield between short-duration grazing and continuous grazing
(Manley et al., 1997; Pitts and Bryant, 1987; Thurow, Blackburn and Taylor,
1988; White et al., 1991). In some cases there was some advantage for shortduration
grazing, depending on stocking rate (Heitschmidt, Downhower and
Walker, 1987). In New Mexico, on blue grama rangeland, short-duration grazing
apparently benefited blue grama compared with continuous grazing (White
et al., 1991). Stocking rate was more influential than grazing system in most of
these studies (Bryant et al., 1989; Holechek, Pieper and Herbel, 2001; Pieper
and Heitschmidt, 1988).
Short-duration grazing apparently reduced infiltration and increased runoff
compared with non-grazed or continuous grazing conditions in grasslands
(McCalla, Blackburn and Merrill, 1984; Pluhar, Knight and Heitschmidt, 1987;
Weltz and Wood, 1986). Concentrating livestock, even for short periods, tends
to compact the soil and negates any possible benefit from hoof action. However,
in New Mexico, infiltration and runoff had returned nearly to normal in shortduration
pastures following the rest period (Weltz and Wood, 1986).
Intensification?
Since grasslands are generally grazed seasonally, provision for feed for the
rest of the year is necessary. The use of complementary pastures along with
native range is one approach for meeting the nutritional needs of livestock
during periods when grazing of native rangeland is not practical (Gillen and
Berg, 2001; Hart et al., 1988; Hoveland, McCann and Hill, 1997; Keller,
1960; Lodge, 1970; Nichols, Sanson and Myran, 1993; Smoliak, 1968). Such
complementary pastures may involve old world bluestems (Gillen and Berg,
2001), introduced grasses such as crested (Plate 6.18) and other wheatgrasses
(Holechek, 1981; Rogler, 1960), other cool-season grasses (Nichols, Sanson
and Myran, 1993) and legumes.
Fertilization is another practice used to enhance livestock performance
in the Great Plains (Nyren, 1979; Wight, 1976). Nitrogen is most often the
limiting nutrient , but in some cases phosphorus and potassium may also be
limiting (Nyren, 1979; Vallentine, 1989; Wight, 1976). An extensive literature
on range fertilization has developed that shows, in general, greater vegetational
response in northern mixed prairie rangelands than in southern areas
(Vallentine, 1989). Nitrogen fertilization may change species composition
by favouring cool-season species if applications are made early in the grow-