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

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Grasslands of the world
their cover. Ordinary grasses, such as Bothriochloa laguroides and Andropogon
ternatus , decrease and Schizachyrium spicatum becomes less frequent than the
others following fertilization, as it is most competitive in a poor environment.
Paspalum plicatulum also decreases with fertilization, although this may be
linked to a palatability increase, as its leaves keep green for longer than unfertilized
grassland . Native legumes increase in frequency, reaching values close to
5 percent. Weeds, typically Baccharis coridifolia , B. trimera and Heimia sp., are
scarce and do not increase with fertilization.
Fertilized grasslands managed under rotational grazing provided the highest
beef production per unit area when stocked with 1.2 AU/ha, and the
highest liveweight gain s per animal at the lower stocking rate of 0.9 AU/ha
(Figure 5.5). At lower stocking rates on fertilized grasslands, steers grew to
440 kg liveweight at 2.5 years, while at the higher stocking rate they did not
exceed 400 kg.
Results can be quite different if the grassland has a high proportion of
summer species and the winter species are mainly annuals, like the soils of the
Crystalline and Eastern Hills. Fertilization at the start of the winter favours
the presence of winter annual grasses such as Vulpia australis and Gaudinia
fragilis , which have limited productive potential at the end of the season. The
disappearance of these species as they finish their growth cycle leaves spaces
that can be occupied by undesirable plants. Spring fertilization increases forage
growth at the end of the summer, when summer grasses flower and produce
seeds. Organic matter digestibility of fertilized forage was greater than unfertilized
grassland (Formoso, pers. comm.). N fertilization increases spring and
summer production markedly, but has little effect on winter growth. This
nutrient increases the frequency of annuals and decreases perennials (Ayala et
al., 1999). N+P fertilization produces a threefold increase in beef production in
comparison with untreated natural grassland.
Fertilization of natural grasslands in southeast Brazil
The quality and production potential of natural grasslands were always
considered to be limited. There was uncertainty about their responses until
Scholl, Lobato and Barreto (1976) showed forage production increases on
natural grassland with N applications in summer , and Barcellos et al. (1980)
obtained significant responses of natural grassland to high P fertilizer rates .
After the results of Rosito and Maraschin (1985) on secondary succession on
fertilized grasslands, a new scenario was clear for southern Brazil , with animal
production results in the Central Depression (Perin and Maraschin, 1995)
similar to those obtained in Campaña fields (Barcellos et al., 1980). On poor
soils of the Central Depression of Rio Grande del Sul (30°S), blanket application
of lime and fertilizers (Moojen, 1991) evaluated five years later (Gomes, 1996)
showed a rise of pH and reduction in Al +++ , while calcium, magnesium and
phosphorus contents of the upper 7.5 cm of the soil increased. Organic matter