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

The South American Campos ecosystem 207
These factors influence the selection of forages to be introduced and the
way the seed will be in contact with the soil, for efficient moisture and nutrient
supply to the seedling. The establishment, productivity and persistence of
introduced forages depends mainly on the way that competition from natural
herbage is reduced, the quality of the seedbed and the adaptation of introduced
species to the environment. Forage yield of improved pastures depends on
soil type and botanical composition , and can be 50 to 100 percent higher than
unimproved grasslands, with winter yield up to three times higher (Berretta et
al., 2000).
Sward preparation for seeding
Generally it is necessary to graze with cattle beforehand to reduce tall-grasses
and accumulated dead material. Stocking rates will depend on forage availability
at the end of the spring and summer , but should be high. If the summer is wet,
grass growth will be high and dry matter and seed stalks will remain at the end
of the season, so stocking must be increased to eliminate this material. Sheep
are used in the final stages, to reduce sward height to 2 cm. This grazing could
be continuous , but rotational grazing is better to allow regrowth and regrazing;
this reduces wild plant reserves , thus favouring the germination, emergence and
establishment of the introduced forages. Depending on grass growth, grazing
must be done every 30–45 days. If grazing is alternated with resting, stocking
rates must be much higher than with continuous grazing . Sward preparation
aims to provide safe sites for good seed-soil contact. Generally it is very
difficult to reduce vegetation cover below 50 percent, although sward height
may be low. Some herbage at sowing time is, however, important to protect
seeds from bad weather.
Chemicals must be used carefully. Non-selective contact herbicides are preferred,
to avoid reducing the growth capacity of native plants. When systemic
herbicides are used, the dose must be low enough to preserve valuable native
species (Berretta and Formoso, 1993).
Legumes for improvement
Many evaluations of different genera and species of legumes have been carried
out. Recent studies include several species of Trifolium , Lotus , Medicago ,
Ornithopus , Desmanthus , Vicia , etc. (Bemhaja, 1998). On medium and deep
soils, the best forages tested have been white clover cvs Zapicán and Bayucuá,
and Lotus corniculatus . Less reliable have been L. pedunculatus cv Maku,
L. hispidus cv. El Rincón and red clover (Trifolium pratense ).
Recommended seed rates are 4–5 kg/ha for white clover , 10–12 kg/ha for
L. corniculatus , 2.5–3.5 kg/ha for L. pedunculatus cv Maku, 4–5 kg/ha for Lotus
cv. El Rincón, 6–8 kg/ha for red clover , and for a mix of white clover and L. corniculatus,
2–3 kg/ha of the former and 8–10 kg/ha of the latter are recommended
(Risso, 1991; 1995; Risso and Morón, 1990).