Research Results - (PDF, 101 mb) - USAID

lished under new rubber trees in four blocks,
Introduced grasses yielded more kg/m2. The
highest yielding introduced grass was Setaria,
followed by Brachiariaand the Panicumspecies.
The local grass Ottochloanodosa had the highest
yield of the local grasses. Stylosanthesguianensis
had the highest yield for the legumes. Asystasia
intrusa,the forb, had yields comparable to most
grasses. These yields were determined monthly
and include the first eight weeks after planting
the rubber trees. The long-term project will
determine pruduction as the tree canopy closes
and the light penetration decreases.
c. Grazing management studies of sheep
under rubber trees
A flock of Sunatran thin-tail ewes
grazed in a rotational system of 12 one-hectare
paddocks under 17-year old rubber trees. Plant
species composition was determined before
starting the rotational system and after one and
two years of grazing. Pasture was improved by
removing non-palatable species after the first
grazing cycle, by planting empty areas with
Paspalumconjugatumand Mikania cordata,and by
spreading manure which had accumulated
under the sheep barn. The main changes in the
vegetation after the first year of grazing were: a
reduction of forbs and an increase in the percentage
of grasses, legumes, total edible plant
species, and area covered with plants. At the
end of the second year of grazing, grasses had
increased to 61.2% of the total species present.
Paspalumconjugatum replaced Mikania cordataas
the dominant species in the pasture. The percentage
of legumes remained the same, so the
increases in grasses were at expense of forbs.
During the first six grazing cycles (406 days) the
stocking rate was 5.76 ewes per ha, and during
the second (395 days) the average stocking rate
was 5.89 ewes per ha.
d. Effects of shading on growth of introduced
forages
An evaluation of shade tolerance was
completed on four local grasses, Axonopus
compresus, Cyrtococcum oxyphylum, Ottochloa
nodosa, andPaspalumconjugatum;three introduced
grasses, Brachiariamutica, Panicummaxi-
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mum var. Hamil, and Paspalumdilatatum;three
legumes, Centrosemapubescens, Clitoriaternatea,
and Stylosanthes guianensisvar. Cook; and two
forbs, Mikenia cordataand Asystasia intrusa. Each
species was planted in four liter plastic pots (45
pots/species) in full sunlight in May, 1989. The
three legumes species and Asystasia was planted
from seed and the others by vegetative propagation.
After a period of 16 weeks a standardization
cut (5 cm from soil) was given to forages
and the pots moved to two locations within each
of four ages of rubber trees: 3.5, 5, 7, and 11
years old. One set of pots remained in the open
in full sunlight and served as the control. There
were five pots per species per location for a total
of 540 pots. To remove the influence of root
reserves present from the full sun establishment,
after eight weeks all pots were harvested at 5cm
above soil level and then the trial began. Two
forage harvest were completed at eight-week
intervals. Measurements of light transmission
were made at the experimental sites on two
occasions using a LICOR instrument which
records the photosynthetic active radiation
(PAR). The estimated values taken between the
two harvest were 0.232,0.087,0.027, and 0.060 of
PAR for the 3.5, 5, 7, and 11 year old trees
utilized in this experiment. Local grasses had
lower yields when compared to introduces
grasses, but there were no differences among
local grasses. Under different shading, Panicum
maximum gave the highest yields of all grasses in
general. Stylosanthes guianensisgave the highest
yields of the three legumes studied. The forb
Asystasia intrusahad the highest yield of all the
species. All the local grasses survived under all
age treatments, supporting their reputation of
shade tolerance. Their decline in productivity
under shade was not as pronounced as with the
introduced grasses. Two of the introduced
grasses, Brachiariaand Paspalumdilatatum,did
not survive the light conditions imposed by the
seven-year old trees. Two legumes, Centrosema
and Clitoria,also survived under all light regimes,
but Clitoriashowed much better yield
with higher shading. Stylosanthes gave a very
high yield in the open, second only to Panicum,
but its yields decreased sharply under shade,
and was the only legume species that could not
grow under 7-year old trees (0.027 PAR). Both
of the forbs grew in all age treatments, but