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

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Grasslands of the world
TABLE 5.10
Production of steers in rotational grazing on improved native grasslands in different regions of
Uruguay .
Soils
Stocking rate
(AU/ha)
Liveweight gain
(kg/ha)
Individual performance
(kg LW/head)
Crystalline 1.55 533 406
Medium and deep Basalt 1.85 680 485
Hills 1.53 (1) 700 473
NOTES: (1) Includes mixed grazing with wethers in a ratio of two wethers per steer.
SOURCE: Adapted from Ayala and Carámbula, 1996; Bemhaja, Berretta and Brito, 1998; Risso and Berretta, 1997.
This improvement technique is low-input and environmentally friendly,
promotes sustainable development of native vegetation and improves productivity
, accelerating fattening by means of better individual performance
and higher stocking capacity (Table 5.10). These results were obtained in
rotational grazing conditions, 5–8 paddocks, 7–12 grazing days and 30–40
rest days, in grazing seasons of about 300 days (Berretta et al., 2000).
Effect of legume introduction on composition of native grasslands
Once legumes have been established for some years, an important change
is an increase of winter grasses (C3 ) (Berretta and Levratto, 1990; Bemhaja
and Berretta, 1991). On similar unimproved grasslands of the basalt region,
summer species are always more frequent than winter ones (Formoso, 1990;
Berretta, 1990). On improved grasslands, the relative frequency of winter
forage species is around 75 percent, with similar values for native grasses
and introduced Trifolium repens . The increased frequency of better quality
species raises the N content of the forage to 3.2 percent.
Flowering and seed production are necessary to maintain introduced
species in the pasture . This ensures regeneration the next autumn , since they
pass the summer partly as plants and partly as seeds (Berretta and Risso,
1995). Reduction or total exclusion of grazing also favours seed production
of native winter grasses, including Poa lanigera , Stipa setigera , Piptochaetium
stipoides and Adesmia bicolor . Therefore conservation of these species in
native grasslands is related both to rest periods to allow flowering and seed
production, and to increased soil fertility. In many improved grasslands, there
is a remarkable increase in the frequency of Lolium multiflorum , which has
adapted, and in many cases is introduced and thrives with increased fertility.
Legume introduction can have positive effects in more degraded grasslands,
dominated by unproductive or unpalatable grasses and short herbs. Relative
legume frequency (Trifolium repens , Lotus corniculatus ) is about 60 percent.
Native, productive winter grasses – Stipa neesiana and Piptochaetium
stipoides – and naturalized species, such as Lolium multiflorum , increase
in frequency, while unproductive grasses and herbs decrease (Berretta and
Risso, 1995; Risso and Berretta, 1997). Oversowing of perennial and annual
legumes in C3 -dominated grasslands that had a yearly forage production of