RESPONSES OF NERICA RICE TO WEED INTERFERENCE IN SAVANNAH UPLANDS

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RESPONSES OF NERICA RICE TO WEED INTERFERENCE IN
SAVANNAH UPLANDS

• I. K. Dzomeku1, W. Dogbe2,
• E. T. Agawu1 and I. T. Duku11University for
  Development Studies, Tamale. 2Savannah
  Agricultural Research Institute, Tamale.
• Africa Rice Congress, Dar Es Salaam Tanzania.
• 31st July 4th August 2006.

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ORDER OF PRESENTATION

• INTRODUCTION
• OBJECTIVE
• MATERIALS AND METHODS
• RESULTS
• DISCUSSION
• CONCLUSION

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1. INTRODUCTION

• With the development of NERICA rice (New African
  rice) varieties by WARDA and the programmed
  dissemination of at least NERICA 1 during the
  2006 cropping season to Ghanaian farmers,
• There was the need for the National Agricultural
  Research system to develop suitable agronomic
  packages for farmers to enhance the performance
  of the crop and farmer adoption rate.

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1. INTRODUCTION 2

• Weeds are major constraint to increased rice
  production and farmers spend many hours hand
  weeding (Akobundu 1987) in face of lack of
  labour (Tollens, 2006).
• Weeds interfere with rice growth and development
  by (1) reducing the available light, nutrient,
  water, CO2 and space, (2) secrete toxic exudates
  into the soil that depress growth and development
  of rice. (3) Harbour various pests (Moody, 1994,
  FAO, 1996).
• The longer the weed-rice association remains,
  greater the reducing effects on rice productivity
  (Akobundu 1987, 1991 Moody, 1994).
• Understanding how long weeds-rice could
  associate without damaging effect on rice is key
  to formulation of sustainable integrated weed
  management alternatives.

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2. OBJECTIVE

• Determine the critical period of weed
  interference (i.e how long can weeds-rice
  coexist for onset of economic loss in rice
  productivity?).
• It is necessary to help determine timing and
  targeting of weed control interventions to most
  crucial periods to avoid economic yield loss,
• Helps to determine single weed control measures
  likely suitable for integration, and
• Helps efficient use and management of farm labor.

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3. MATERIALS AND METHODS

• Location of Trials Tamale at the Savannah
  Agricultural Research Institute (SARI) in the
  Northern Guinea Savannah ecological zone of
  Ghana.
• Rainfall Unimodal pattern-mean annual rainfall
  of 1000-1200mm. Fairly distributed from
  April-November.
• Temperature -mean monthly minimum of 23.4C and
  maximum of 34.5C.
• RH Minimum RH of 46 and maximum of 76.8 (SARI
  Annual Report, 1997).

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3.1. Experimental design and materials used

• Ten treatments were compared in a randomised
  complete block design in four replications.
• In one set of treatments, plots were kept
  weed-free up to 3, 6, 9 and 12 WAP and
  subsequently left weed-infested until harvest.
• In the other set of treatments weeds were allowed
  to interfere with the crop for periods up to 3,
  6, 9 and 12 WAP and subsequently kept weed-free
  until harvest.
• Two checks were included as full-season
  weed-infestation or season-long weed-free regimes

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3.2. Agronomic practices 1

• Weeding was done every 3 weeks, starting from
  the third week after planting with a small hand
  hoe.
• Plot size was 5 m 5 m,
• New Rice for Africa (NERICAs 1 and 2 were
  evaluated in experiments 1 and 2 respectively).

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New Rice for Africaat maturity

• NERICA 2

• NERICA 1

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3.3. Agronomic practices 2

• Fertilizer rate of 60-60-30 kg/ha NPK was applied
  as split,
• basal fertilizer at a rate of 30-60-30 kg/ha at
  2 WAP.
• N with urea fertilizer drilled between drills
  second application was broadcasted 5-6 WAP.

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3.4. Data collected (SES)

• Soil gravimetric moisture content ()
• Plant height
• Leaf area index (Watson, 1952)
• Tiller count/m²
• Weed species and species dominance
• Straw weight
• Grain yield

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3.5. Weed species and species dominance

• 1 m² quadrat sampling unit for weed dominance
  data and identification.
• The quadrat was thrown on the two diagonal
  transects of the field for frequency and density
  data summed dominance ratio (SDR) of weeds,
  determined by the relationship
• ½ (F/?F D/?D), where F frequency of
  occurrence of a weed within the field, D
  density of its occurrence on the scale of 0-4,
  where 0 zero occurrence of a species per 1m²
  and 4 20 stands of weed (Dangol, 1991).

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4. RESULTS 4.1. Gravimetric soil moisture
content

• Site 2

• Site 1

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4.2. Plant height of NERICAs at 12 WAP

• NERICA 1

• NERICA 2

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4.3. Plant height of NERICAs at 15 WAP

• NERICA 2

• NERICA 1

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4.4. LAI of the NERICAs at 50DAP

• NERICA 2

• NERICA 1

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4.5. Tiller count/m² of Nerica 1 at 50DAP

• NERICA 2

• NERICA 1

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4.6. Straw yield of NERICA 1-site 1
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4.7. Grain yield of NERICA 1 - site 1
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4.8. Grain yield of NERICA 2 - site 2
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NERICA 1
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Nerica 2
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Table 2. Relationship between grain yield and
growth parameters of NERICA 1 and 2
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Table 2. Relationship between growth parameters
and grain yields of Nerica 1 2.
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5. DISCUSSION 1

• Changes in gravimetric soil moisture content
  could be attributable to the fluctuation in
  rainfall during the season.
• The fluctuation did not however, show any visual
  effect on the vegetative phase but potentially
  yields could been higher under more stable
  moisture.
• The varieties however have an in-built ability to
  withstand short periods of drought (WARDA, 1999).

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5. DISCUSSION 2

• At 12 and 15 WAP, the mean plant height for plots
  weeded for 6 weeks or more were similar to the
  weed-free check suggesting the required optimum
  weeding regime to maximise plant height was c. 6
  WAP.
• Indeed the 2 varieties attained 100 cm plant
  height within 6 WAP under 6 weeks of continuous
  weeding.

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5. DISCUSSION 3

• Similar to other results, crops kept weed-free
  until harvest gave maximum LAI value similar to
  plants given continuous weeding up to 6-12 WAP
  showing absence of weed interference within 6
  WAP, could optimise attainment of LAImax.
• Weed infestation of the Nericas exceeding 6 WAP
  timings resulted in poor LAI, suggesting that the
  crop is a poor competitor with weeds beyond this
  period of development.
• Usually LAI of rice is closely related to grain
  yield because at flowering it greatly affects the
  amount of photosynthates available to the panicle
  (Yoshida and Parao, 1976).

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5. DISCUSSION 4

• Crops kept weed-free at least up to 6 WAP had
  better tillering plants kept initially
  weed-infested and until harvest probably due to
  the genetic tillering ability of ativa parent.

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5. DISCUSSION 5

• Grain and straw yields was optimised by crops
  kept weed-free for at least up to 6 WAP
  suggesting the frequent removal of weeds
  eliminated weed interference resulting in
  enhanced growth performance such as in tiller
  numbers, with consequential higher grain and
  straw yields.
• Notably an initial weed infestation for only up
  to 3 WAP did not affect most parameters including
  the grain yield compared with weed-free check. In
  effect, early weed infestation for maximum period
  of 3 WAP before weed removal might not cause any
  yield reduction.

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ACKNOWLEDGEMENT

• We are grateful to WARDA for financial support
  for the project and sponsorship of the Congress

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6. CONCLUSION

• Weed infestation 6WAP or more significantly
  depressed grain yield and other growth
  parameters, especially plant height (at 12 and
  15WAP), LAI and tiller count/m².
• Initial weed infestation up to 3 WAP did not have
  adverse effect on the varieties.
• Weed-free environment up to 6WAP recorded notably
  similar grain yield, LAI and tiller count/m²
  with the weed-free check.
• The critical period of weed interference likely
  lies between 3 and 6 WAP(as reported for rice
  Akobundu, 1987).
• As such two hand weedings at 3 and 6WAP could
  protect the crops against weed interference with
  consequential optimum productivity of Nerica 131
  and 2.

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Thank you