Seed production of two brachiaria hybrid cultivars in - Tropical ...

Seed production in brachiaria hybrids 27
high forage seed quality, smallholder experience
and professionalism and public sector involvement
in forage seed production in Thailand (Hare
and Horne 2004). Grupo Papalotla also wanted
to break into the Asian market for forage seed.
In addition, there was an expectation that seed
yields of brachiaria hybrids might be higher in
Thailand (because of intensive agronomic management
and hand harvesting of seed from small
fields) than in Brazil and Mexico under extensive
management and machine sweeping of seed from
the ground from large fields. Low seed yields in
Brazil and Mexico (less than 200 kg/ha) meant
that the price of brachiaria hybrid seed was 3–4
times that of seed of other commercial Brachiaria
spp. in Latin America.
Field trials commenced at Ubon Ratchathani
University, Thailand, in 2003 to investigate agronomic
management of brachiaria hybrids in order
to increase seed yields. A series of trials investigated
the effects of method and time of planting,
closing date defoliation and harvesting methods
on seed production of cvv. Mulato and Mulato
II. This paper reports the results of studies on
method and time of planting.
Establishing grass seed crops with seed in rows
is the preferred method of establishment in Brazil,
but in Australia, broadcasting seed through a fertiliser
spreader is the common practice. Time of
sowing for seed crops depends primarily on the
reliability of rainfall, increasing temperatures and
potential evapotranspiration during the growing
season (Loch et al. 1999). Early sowings generally
produce the most seed and have the added
advantage of forage production from a closing
cut. All Brachiaria spp. seed crops in Brazil
(Souza 1999) and brachiaria hybrid seed crops in
Mexico and Brazil (E. Stern, personal communication)
are established by sowing seed.
However, method and time of seed crop
establishment can significantly affect grass seed
yields in Thailand. Crops of Paspalum atratum
cv. Ubon failed to produce seed in the first year
when established by sowing seed (Hare et al.
2001). P. atratum seed crops planted with tillers
in May and early June produced 2–3 times more
seed than crops planted from mid-June to mid-
July. Farmers plant commercial seed crops of
B. ruziziensis using seed from late May to late
June (Hare and Phaikaew 1999), whereas all
commercial seed crops of Panicum maximum cv.
Purple are planted with tillers in July (M.D. Hare,
unpublished observations).
The hypotheses tested in this research are
that: brachiaria hybrid seed crops established by
planting tillers produce more seed than crops established
by seed; and early-established crops produce
more seed than later-established crops. The
main objective was to measure the seed production
of brachiaria hybrids planted with seed or with
tillers.
Materials and methods
Four field experiments were conducted in Ubon
Ratchathani province, north-east Thailand (15°N,
104°E; 130 m asl; AAR 1538 mm) on the Ubon
Ratchathani University farm in a 0.15 ha field
from 2003 to 2005. Annual rainfall was recorded
at the trial site (Figure 1). The site was on an
upland sandy low humic gley soil (Roi-et soil
series) (Mitsuchi et al. 1986). Soil samples to
10 cm, taken in May 2003, showed that the soil
was acid (pH 4.8; water method), and low in
organic matter (0.9%), N (0.03%), P (4.9 ppm;
Bray II extraction method) and K (53.6 ppm).
Prior to cultivation, the site had been planted to
Stylosanthes guianensis var. vulgaris × paucifl ora
(ATF 3308) for 2 years.
Trial 1 — Effect of time of seed sowing on seed
production of Mulato
Four sowing dates (May 6, June 6, July 6 and
August 6, 2003) were compared in a 5-replicate,
randomised complete block field experiment. Seed
(5 kg/ha) was sown at a spacing of 50 cm × 50 cm
into well cultivated plots of 4 m × 5 m. To increase
seed germination to 70%, the seed was scarified
in sulphuric acid for 10 minutes, washed in
running cold water and dried before sowing. Fertiliser
(NPK 15:15:15) was applied at the rate of
160 kg/ha to each new plot at sowing and again to
all plots on September 20, 2003. On August 1, the
May-planting treatments were cut to 10 cm above
ground level, dry matter yield was measured from
2 m of 3 rows in each plot and crude protein
concentrations were determined.
At peak anthesis, all inflorescences in a fixed
1 m × 2 m quadrat were counted and 20 inflorescences
harvested from just outside this quadrat
for reproductive assessment. All racemes were
counted on each inflorescence and spikelets were
counted on 3 racemes per inflorescence, taken