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

The South American Campos ecosystem 197
With increasing levels of FO , ground cover increases; as leaves increase in
relation to stems, forage and animal production also increase. The PAR/SP
[Secondary Production] relationship nearly doubles when FO changes from
4.0 to 12.0 percent LW. Maximum LW is attained at lower stocking rates , which
are exactly those that promote high DLWG , related to high AR and light grazing
. The Primary Aerial Productivity (PAP):SP relationship had an efficiency
of 4.48 percent with an FO of 4.0 percent, reaching 4.66 percent with an FO of
12.0 percent, as a consequence of increased DLWG . Lighter grazing pressures
allow tall species to make important contributions to increase animal diet quality,
and also protects native fauna.
Optimal utilization ranges for natural grasslands can be derived from a curvilinear
response model , promoting productivity and ensuring sustainability ,
which is attained by higher utilization efficiency of incident PAR (Table 5.6
and Figure 5.3). Optimal utilization ranges are estimated from FOs of 13.5 percent
of LW (maximum DLWG per head) to 11.5 percent of LW (maximum
LW), where there is compromise between individual and per-hectare production.
As there is considerable variation between the nutritional requirements
of species and classes of animal (cow+calf, ewe+lamb, heifers, steers, bulls,
horses, etc.) each pasture has to be managed according to the specific animal
class requirements. Stocking rate and carrying capacity can only be defined as
a function of the animal product involved and cannot be fixed, because they
depend on environmental variations.
Table 5.7 can be prepared as a function derived from the grassland optimization
model , which reflects natural grassland grazing optimization and the
stocking rate that this pasture could feed at optimal carrying capacity . In the
warm season – a nearly 200-day grazing period for natural grassland – these
results adjust to the animal product yield equation in the following way:
Yield = Quality × Quantity
Liveweight/ha (LW) = DLWG × Animal-day/ha
146 kg = 0.517 kg × 282
Forage harvest from natural grasslands could be improved , representing an
annual increase of 784 000 t live weight, without cost, in Rio Grande do Sul
alone through the recommended strategy of high FO to the grazing animal,
TABLE 5.7
Natural grassland and animal performance in the optimal utilization range.
Parameters Responses
DM/ha/day (kg) 16.30 (evaluated)
Animal-day/ha 282 (counted)
Daily LWG (kg) 0.517 (evaluated)
Liveweight gain /ha (kg) 146 (calculated)
Carrying capacity 1.17 two-year-old steers (calculated)
Stocking rate (kg/ha) 370 (observed)