Direct seeding of rice (Oryza sativa 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 Cyperus rotundus, Isachne globosa and Leptochloa chinensis. In DWSR, the dominant species were Cyperus rotundus, Echinochloa crus-galli and Isachne globosa. The weed density was reduced in the WS and the major weeds were Cyperus rotundus, Echinochloa crus-galli and Isachne globosa. In both systems Cyperus rotundus 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.
The impact of a rice straw mulch (RSM) under optimal mineral fertilized conditions on growth, yield components and yield of dry-direct seeded (DDSR) and wetdirect seeded rice (WDSR) was evaluated under field conditions over four consecutive seasons to include two dry (DS) and two wet (WS) seasons, in the dry zone of Sri Lanka. The RSM could be applied in WDSR in both seasons and DDSR in WS at a rate of 4t/ha without affecting the seedling density. RSM in WDSR, especially at initial stages of plant growth (i.e. 35 days after sowing) increased plant height, length of the longest root and total root length significantly than in non mulched and DDSR-RSM plots. Shoot and root biomass were also significantly increased by RSM in WDSR in both seasons. Rice straw mulch increased panicle number per unit area and number of spikelets per panicle in WDSR-RSM in both seasons. A significantly high yield could be achieved in WDSR-RSM, WDSR-chemical weeding (C) and DDSR-C treatments in both seasons. The yield enhancement was attributed to yield components, principally panicle number per unit area and number of spikelet per panicle. There was a greater panicle number per unit area in the DS while the WS favors more spikelets per panicle. The study indicated the possibility of enhancing the rice plant growth, yield components and yields of rice in wet-direct seeded lowland rice by rice straw mulch in both seasons in this region.
A field experiment was conducted to compare the growth, physiology, weed abundance and yield in rice under three input systems; organic, conventional and integrated, during the 2019 Yala season as the second season of a long-term cropping systems trial. The design used a Randomized Complete Block Design (RCBD), with six (6) replicates for each treatment. The rice variety used in the experiment was Bg 300 and three treatments were based on three input systems such as T1 -Conventional input system (100% Department of Agriculture (DOA) inorganic fertilizer recommendation), T2 -Integrated system (50% of Department of Agriculture (DOA) inorganic fertilizer recommendation+50% of the rate of compost added to organic input system) and T3 -Organic system (No inorganic fertilizers and only compost with the rate of 10000 kg ha -1 ). At the panicle initiation and harvesting stages, there was a (p<0.05) significant difference (in rice shoot biomass across the three input systems, with the organic system having the
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