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This paper explores the role of some of these ecological processes in influencingthe structure of the weed community of rainfed rice and considers the implications forthe development of weed control strategies. Although TPR and hand weeding havetraditionally met the goal of minimizing weed presence, the use of early postemergenceherbicides in DSR rarely achieves total weed control. Staggered weed emergence,variation in the length of the life cycle of weed species that persist after postemergencechemical control, and spatial escapes contribute to the need for further weedcontrol, which is often manual. Identifying the factors determining the compositionand size of this weed flora in relation to crop and weed management is important inthe choice and cost of late postemergence weed control practices. This paper drawson observations and data analysis from a long-term cropping trial started in 1999 inthe northwest Barind (Rajshahi District).Materials and methodsField experimentAs described elsewhere (Mazid et al 2006; this volume), experimental comparison ofrice establishment methods on rice yields and weed responses was made in successiveyears from 2001 to 2004. These methods were (1) transplanted rice—soil puddledprior to transplanting and plots hand-weeded twice at 30 and 45 days after transplanting(DAT); (2) direct-seeded rice (DSRm)—soil plowed prior to dry seeding (2001and 2004) or plowed and puddled before direct seeding of pregerminated seed (2002and 2003) in rows by hand with hand weeding at 21, 33, and 45 days after sowing;and (3) direct-seeded rice with chemical weed control (DSRh)—as above but withoxadiazon (375 g a.i. ha –1 ) applied 2–4 days after seeding with one hand weeding at33 days after sowing (DAS). With failure in development of the monsoon in 2003,transplanting was delayed substantially (Fig. 1) until September and the crop wasestablished only for experimental purposes. Data from this experiment are discussedonly for the 2002 and 2004 seasons.Water regimesMeasurements of the water table began in the field experiment in relation to intensityof the onset of the monsoon with the use of fixed pizometers that extended 20 mmabove ground. No standing water was observed prior to the first recorded measurementin each season.Soil nutrient analysisFour nutrient regimes were applied in factorial combination with other treatments inthe field experiment. These were (kg ha –1 ) (1) single superphosphate, 40 P + 40 K;(2) compound, 60 N + 40 P + 40 K; (3) farmyard manure (FYM) + inorganic fertilizertotaling 60 N + 50 P + 50 K; and (4) diammonium phosphate (18% N) + Gutislow-release urea (45% N) totaling 43 N + 40 P + 40 K. At the conclusion of the experiment,bulk soil samples were taken from individual plots to a depth of 20 cm andsoil nutrient analysis was completed for total organic matter (combustion), potassiumLong-term sustainability in weed management for direct seeding of rainfed rice 69
Days from 1 JulyDays from 1 JulyFig. 1. Rainfall patterns, cropping calendar,and standing water status (mean ± S.E.)measured by pizometer in three successivecropping seasons. All data are aligned to acommon time scale. In 2002 (A) and 2003(B), wet seeding was used for sowing. In 2004(C), rice was dry-seeded. Solid circles indicatedates of land preparation and open circlesdates of sowing. DSR = direct-seeded rice,TPR = transplanted rice, CP = chickpea. In2003, failure in development of the monsoonled to substantial delay in transplanting. % soilmoisture for three soil depths is given afterestablishment of DSR.Days from 1 July70 Mortimer et al
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Improving AgriculturalProductivity
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Bangladeshi experiences with a drum
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AcknowledgmentsIRRI is most gratefu
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The High Barind Tract: a challengin
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irrigation across the entire Barind
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Workshop synthesis
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and, with representatives from the
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Subsistence pressureLand pressure,
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HerbicidesEarlier efforts to introd
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volume). PVS is an effective way to
Page 27 and 28: Farmers may use wet-seeded DSR as a
Page 29 and 30: process and distributing HNPV to fa
Page 31 and 32: an NGO, have successfully collabora
Page 34 and 35: Workshop discussionParticipants dis
Page 36 and 37: How can we identify a short-duratio
Page 38 and 39: to fixed tenancy. The implication i
Page 40: Opportunities for improving ricepro
Page 43 and 44: that the reliability and productivi
Page 45 and 46: Table 1. Planting dates, direct-see
Page 47 and 48: Table 2. (A) Mean effect of fertili
Page 49 and 50: Table 5. On-farm trials of a drum s
Page 51 and 52: Upper toposequenceYield (t ha -1 )7
Page 53 and 54: and perennial grasses (e.g., Ischae
Page 56 and 57: Direct-seeded rice in the HighBarin
Page 58: Table 1. Sample selection for costs
Page 61 and 62: Table 4. Variations in weed managem
Page 63 and 64: Table 7. Labor requirements (days h
Page 65 and 66: Table 10. Farmer perceptions of dis
Page 67 and 68: Farmers (no.)1412108DSRWet-seededDr
Page 69 and 70: able commercially. Other OFT farmer
Page 71: Box 1. Farmers’ comments on DSRPo
Page 74: NotesAuthors’ addresses: M.A. Jab
Page 80 and 81: (Olsen method, atomic absorption),
Page 82 and 83: Mean biomass (g m −2 )1,000.000Fi
Page 84 and 85: Fig. 3. Log rank abundance of weed
Page 86 and 87: attested by Fig. 2). Diversity in t
Page 88 and 89: Bangladeshi experiences with a drum
Page 90 and 91: Table 1. Grain yield and crop durat
Page 92 and 93: Table 5. Grain yield and growth dur
Page 94 and 95: ACEy = 0.0001x + 0.7089Yield (t ha
Page 96 and 97: Table 11. Partial budget analysis f
Page 98: ConclusionsDirect wet-seeded rice u
Page 101 and 102: A 178% increase in rice production
Page 103 and 104: Table 1. Components of yield gaps d
Page 105 and 106: Table 3. Weed management in Comilla
Page 107 and 108: Table 5. Weed management practices
Page 109 and 110: Table 7. Significance (P H o ) of t
Page 111 and 112: Since 2000, there has been an incre
Page 114 and 115: Identifying varieties for the High
Page 116 and 117: Table 1. Rice varieties bred by cli
Page 118 and 119: Table 2. Grain yield advantage of J
Page 120 and 121: Table 3. Plant height and crop dura
Page 122 and 123: Table 6. Summary of adoption and sp
Page 124 and 125: Freeman GH, Perkins J.M. 1971. Envi
Page 126: Opportunities for improving rabi cr
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Grain yield (t ha -1 )2.0npp1.5LSD
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In each of the plots, numbers of He
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Table 2. Effect of IPM components o
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Unit plot size was 10 10 m and the
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Yield (t ha -1 )5Straw4321GrainP (g
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Nodulation score3AControl Soil Mo P
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even at low levels of production. B
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Integration of chickpea and other r
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Grain yield (t ha -1 )3.02.51989-99
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Improved Improved Rainfed rainfed C
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Table 1. Preharvest and postharvest
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Greater resistance to Helicoverpa p
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wheat varieties). There is also sco
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Developing seed systems fordissemin
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This paper describes attempts to em
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seed needed to attain the recommend
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introduced to permit sale beyond th
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pesticides, inoculation with benefi
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for the rabi crop in 2001. Hence, b
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where farmers decided not to relay-
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Table 2. Mean dates of T. aman harv
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Table 4. Subsistence pressure and r
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Table 7. Subsistence pressure and r
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cite the absence of rent as a facto
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abi cropping in the HBT through ear
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Formulation and dissemination ofimp
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in India, for which shorter-duratio
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Applied researchOFTsAdaptive resear
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Table 1. Recommended package of pra
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Table 2. Grain yields (kg ha -1 ) o
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Table 4. Grain yields (t ha -1 ) of
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Table 6. Mean grain yields (t ha -1
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constraints present. This in itself
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Extending rabi cropping in rice fal
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Table 1. Estimates of rice area dur
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Yield (kg ha -1 )1,2001,00080060040
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Future disseminationThrough dialogu
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Direct seeding of rice andopportuni
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Table 1. Time of establishment and
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Table 3. Weed density and biomass a
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than in Central Java and many farme
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Proportion abundance (log scale)Ran
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CAN FIELD BE DRAINED?YesCAN FIELD B
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Johnson DE, Mortimer AM. 2005. Issu
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Zhao DL, Atlin GN, Bastiaans L, Spi
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