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(Olsen method, atomic absorption), total N (Kjeldahl), and phosphorus, sulfur, boron,and zinc (spectrophotometrically following acid digestion).Soil seed banksThree replicate soil samples (each 1,000 cm 3 ) were taken from individual plots oneach of two occasions, after rice cropping in 2000 and 2002. Soil was then dried andsamples pooled according to plot treatment with thorough mixing. Soil from the 2000field sampling was stored until 2003. Samples (1 kg) of mixed soil for each sampleyear were then spread according to plot treatments in shallow trays that were wateredto either permanently maintain saturated or aerobic conditions. Emerging seedlingswere identified by species, counted, and removed. Soil was then stirred to promote asecond and third flush. Data were pooled at the plot level to provide an overall estimateof the size of the seed bank for each recorded species.Results and discussionThe weed flora in the study region was typically diverse, including grass, sedge, andbroadleaf species (Table 1). These included ubiquitous major weeds of rice such asCyperus rotundus, C. iria, C. diffusa, Ischaemum rugosum, Echinochloa colona, E.crus-galli, and Monochoria vaginalis.Figure 1 illustrates the variation in water regimes and the presence of pondedwater during three rice cropping seasons. In all years, DSR was established in advanceof TPR with the onset of the monsoon and in 2002 and 2003 soil conditionsprecluded the drilling of rice and wet-seeded rice was sown, whereas in 2004 ricewas drill-seeded. Ponded water was absent in the first 14 days after rice sowing and intransplanted plots standing water depths were shallow and temporally variable. Therewere no large differences in the weed flora between transplanted and direct-seededplots (unweeded at 45 DAT/DAS when the principal phase of weed recruitment hadoccurred), although individual species differed in relative abundance and some specieswere absent in some instances. More noticeable differences in the composition ofthe weed flora between TPR and DSR would be expected if standing water had beendeep and persistent (≥10 cm). However, species that required prolonged saturated soilconditions to promote germination and establishment (for example, M. vaginalis) weremore abundant under TPR than under wet-seeded rice (WSR) in 2002 and 2003. Logrank abundance curves (Fig. 2) were either linear or log normal, S-shaped Ulrich andOllik (2005), statistical analysis not shown). The presence of a log normal distribution(for example, in WSR and TPR in 2003) is suggestive of high habitat heterogeneity,whereas the occurrence of an upper tail indicates species that are disproportionatelyabundant. Among the dominant sedges, Fimbristylis miliacea was replaced by F. dichotomain the relatively drier conditions of 2003 compared with 2002 and 2004 andCyperus difformis exhibited greater abundance than C. iria under wet rather than dryseeding. These observations suggest subtleties in the germination ecology of thesesedges. Cynodon dactylon was recorded in the weed flora in all three seasons underboth crop establishment methods. The most diverse weed flora was recorded in 2004Long-term sustainability in weed management for direct seeding of rainfed rice 71
Table 1. Weed species recorded at the study location. Species were identified by observationin the experimental area and by scouting in nearby farmers’ fields.NameAeschynomene indica L.Alternanthera sessilis (L.) R. Br. ex DC.Ammannia baccifera L.Commelina diffusa Burm. f.Cyanotis axillaris (L.) D. Don ex SweetCynodon dactylon (L.) Pers.Cyperus difformis L.Cyperus iria L.Cyperus rotundus L.Cyperus haspan L.Dopatrium junceum (Roxb.) Buch. Ham. ex Benth.Echinochloa colona (L.) LinkEchinochloa crus-galli (L.) P. Beauv.Eclipta prostrata (L.) L.Eriocaulon cinereum R. Br.Fimbristylis miliacea (L.) VahlFimbristylis dichotoma (L.) VahlHedyotis corymbosa (L.) Lam.Hydrolea zeylanica (L.) VahlIschaemum rugosum Salisb.Lindernia ciliata (Colsm.) PennellLindernia speciesLudwigia adscendens (L.) HaraLudwigia groupLudwigia hyssopifolia (G. Don) ExellMarsilea minuta L.Monochoria vaginalis (Burm. f.) Presl C. ex KunthPaspalum distichum L.Paspalum vaginatum Sw.Rotala speciesSagittaria guayanensis KunthScirpus supinus L.Sphaeranthus indicus L.Sphenoclea zeylanica GaertnerSpecies codeAes_indAlt_sesAmm_bacCom_difCya_axiCyn_dacCyp_difCyp_iriCyp_rotCyp_tenDop_junEch_colEch_cruEcl_proEri_cinFim_milFim_dicHey_corHyd_zeyIsc_rugLin_cilLin_sppLud_adsLud_sppLud_hysMar_minMon_vagPas_disPas_vagRot_sppSag_guySci_supSph_indSph_zeyin dry-seeded plots after three previous seasons of direct seeding, with E. colona, E.crus-galli, I. rugosum, and C. rotundus being present.Figure 2 shows the influence of weeding by manual or chemical means at 21DAS/DAT on the weed flora present 12 days later in 2004. Total weed biomass inplots was reduced by up to two orders of magnitude in comparison with biomass at45 DAS/DAT in unweeded plots but neither method of weed control had achievedweed-free plots. More weed biomass was present in DSR plots than in TPR plots. Inparticular, the use of oxadiazon resulted in the dominance of Cynodon dactylon andPaspalum distichum.72 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
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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 78 and 79: This paper explores the role of som
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
Page 129 and 130: 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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