Abstract
Direct seeding of rice (<em>Oryza sativa</em> L.) induces the production of greater grain yields in water deficit areas. However, weeds pose a serious threat to sustainability of yield of direct-seeded rice. This field study evaluated the effectiveness of rice straw mulch on managing weed populations and increasing yields of direct wet-seeded (DWSR) and direct dry-seeded rice (DDSR) in 2009 Yala (DS) and 2009/2010 Maha (WS) seasons in a principal rice growing region of Sri Lanka. The major weeds associated with DDSR in DS were <em>Cyperus rotundus</em>, <em>Isachne globosa</em> and <em>Leptochloa chinensis</em>. In DWSR, the dominant species were <em>Cyperus rotundus</em>, <em>Echinochloa crus-galli</em> and <em>Isachne globosa</em>. The weed density was reduced in the WS and the major weeds were <em>Cyperus rotundus</em>, <em>Echinochloa crus-galli</em> and <em>Isachne globosa</em>. In both systems <em>Cyperus rotundus</em> was the most dominant weed species in all treatments based on the summed dominance ratio. The rice straw mulch was effective in weed management under DWSR, but not in DDSR. The grain yield was inversely correlated with increasing weed biomass and weed density in both systems. Compared to DWSR, chemical weeding which is the present practice in Sri Lanka, yield gains of 9.23% and 5.74% were achieved in DWSR with a straw mulch and a yield loss of 49.88% and 22.24% in the DDSR with the same treatment in DS and WS, respectively. The study indicated the possibility of suppressing weeds in direct wet-seeded land low rice with straw mulch in both seasons. <strong>Key words</strong><strong>: </strong>Direct dry-seeding; direct wet-seeding; grain yield; rice straw mulch; weed management DOI: <a href="http://dx.doi.org/10.4038/tar.v22i3.3699">http://dx.doi.org/10.4038/tar.v22i3.3699</a> <em>Tropical Agricultural Research </em>22(3) (2011) 263-272<em> </em>
Highlights
Rice (Oryza sativa L.), the staple food crop for about half of the world population, is mainly grown in South and South-east Asia
This study aims to contribute to the development of sustainable integrated weed management systems and seek the possibility of minimizing herbicide use in direct seeded rice cultivation
The major weeds associated with direct dry-seeded rice (DDSR) in the 2009 DS were Cyperus rotundus, Isachne globosa and Leptochloa chinensis while in DWSR the major weeds were C. rotundus, Echinochloa crus-galli and Isachne globosa
Summary
Rice (Oryza sativa L.), the staple food crop for about half of the world population, is mainly grown in South and South-east Asia. There are three principal methods of rice establishment: dry seeding, wet seeding, and transplanting. These methods vary, each one is characterized by distinct features. Dry seeding consists of sowing dry seeds onto dry (unsaturated) soils. Wet seeding involves sowing pre-germinated seeds onto wet (saturated) puddled soils. Transplanting involves replanting of rice seedlings grown in nurseries into puddled soils. When seeds are sown directly, the dryand wet-seeding methods are often jointly referred to as direct seeding. In response to rising labor costs, competitive demand for water and the need to intensify crop production, many Asian farmers have shifted from transplanting to direct seeding of rice (Pandey and Velasco, 1999)
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