here - IRRI books - International Rice Research Institute

Huke RE, Huke EH. 1997. Rice area by type of culture: South, Southeast,
and East Asia. Manila (Philippines): International Rice
Research Institute. 59 p.
Isvilanonda S. 1990. Effects of pregerminated direct seeding technique
on factor use and the economic performance of rice
farming: a case study in an irrigated area of Suphan Buri. In:
Fujimoto A, editor. Thai rice farming in transition. Tokyo (Japan):
World Planning Commission.
Kim SC. 1995. Weed control technology of direct seeded rice in
Korea. Paper presented at the International Symposium on
Weed Control under Direct Seeded Rice, 31 July 1995,
Omagari, Akita, Japan.
Palaniappan SP, Purushothaman S. 1991. Rainfed lowland rice farming
system in Tamil Nadu (India): status and future thrust. In:
Proceedings of the Rainfed Lowland Rice Farming Systems
Research Planning Meeting, Myanmar, August 1991. Manila
(Philippines): International Rice Research Institute.
Pandey S, Velasco LE. 1998. Economics of direct-seeded rice in
Iloilo: lessons from nearly two decades of adoption. Social
Sciences Division Discussion Paper. Manila (Philippines):
International Rice Research Institute.
Pandey S, Velasco LE. 1999. Economics of alternative rice establishment
methods in Asia: a strategic analysis. Social Sciences
Division Discussion Paper. Manila (Philippines): International
Rice Research Institute.
Pandey S, Velasco L, Masicat P, Gagalac F. 1995. An economic analysis
of rice establishment methods in Pangasinan, Central
Luzon. Social Sciences Division Discussion Paper. Manila
(Philippines): International Rice Research Institute.
Pathinayake BD, Nugaliyadde L, Sandanayake CA. 1991. Direct
seeding practices for rice. In: Sri Lanka in direct-seeded
flooded rice in the tropics. Manila (Philippines): International
Rice Research Institute.
PhilRice-BAS (Bureau of Agricultural Statistics). 1995. Provincial
rice statistics. Muñoz, Nueva Ecija (Philippines): Philippine
Rice Research Institute.
Notes
Authors’ address: International Rice Research Institute, e-mail:
sushil.pandey@cgiar.org.
Direct seeding and weed management in Korea
Soon-Chul Kim and Woon-Goo Ha
In 1991, the Rural Development Administration (RDA) introduced
dry drill seeding and water seeding of rice with water
seeding being either wet-drill-sown or water broadcast-seeded.
Despite problems, the direct-seeding area has increased rapidly;
however, only about 8–9% of the total rice area was under
direct seeding in 2003 (RDA 2003). The main constraints
to direct seeding are weed problems and rainfall fluctuation
during seeding time.
Weed ecology in direct-seeded paddy
Weed growth is greatly influenced by cultivation method (Kim
et al 1992) and thus the adoption of direct-seeding technology
results in shifts in weed growth in terms of dry matter production
and composition of dominant species. The greatest weed
growth is recorded in dry-seeded rice, followed by waterseeded
rice, mechanically transplanted rice, and manually transplanted
rice (Table 1).
Early rice growth and water management are considered
as the main factors accounting for the above differences. Yield
losses from weed competition are related closely to weed
growth, with complete crop loss occurring where weeds are
not managed. Changes in crop establishment method from
transplanting to direct seeding changed not only weed dry
matter production but also the composition of the weed species.
In transplanted rice fields, the most troublesome weeds
were Eleocharis kuroguwai (20%), Sagittaria trifolia (16%),
S. pygmaea (13%), Echinochloa crus-galli (12%), and
Monochoria vaginalis (11%) (Kim et al 1992). Approximately
50% of weed biomass was accounted for by perennial weeds.
In dry-seeded rice, on the other hand, annual grasses were the
most predominant weeds, such as E. crus-galli (54%), Digitaria
adscendens (9%), Leptochloa chinensis (8%), Setaria viridis
(6%), and weedy rice (Oryza sativa subsp. spontanea, 5%). In
water seeding, E. crus-galli (37%) was also the most important
weed species even though the degree of dominance was
lower than in dry-seeded rice. The second most important weed
was Aneilema keisak (15%), followed by Ludwigia prostrata
(11%) and Leersia japonica (7%). Weed growth in directseeded
rice was dominated by E. crus-galli, which became the
most important weed and had a slightly lower value in waterseeded
rice than in dry-seeded rice. Most of the annual grass
weeds occurring in direct-seeded rice fields belonged to the
C 4 photosynthetic pathway (Table 2).
Recently, weedy rice (including red rice) has become
widely distributed in farmers’ fields. The possible origins of
weedy rice were summarized by Kim (1995b) as follows:
Shattered grains of the previous year
Outcross between cultivated rice species
Outcross between cultivated rice and red rice (dormant
seeds)
Outcross between wild-type rice and weedy rice (red
rice)
Outcross between red rice species
Dormant red rice or wild-type rice itself
The degree of contamination by weedy rice observed in
fields was highly variable, ranging from 0.5% to 35.2% for
the southern area. However, it was difficult to estimate the
correct degree of contamination and distribution pattern for
all farmers’ fields because field observations were made and
Session 6: Trends in crop establishment and management in Asia 181