ABSTRACT
Field trials were conducted in 2015, 2016 and 2017 cropping seasons at the National Cereal Research Institutes’ farm, (NCRI), Amakama (07˚29′N latitude and 05˚28΄E longitude), South Eastern Nigeria to investigate complementary weed control potential of time of planting and population of sweet potato on cassava (TME 419). The study was laid out in a split plot arrangement in a Randomized Complete Block Design (RCBD) with three replicates. Intercropping patterns which included two populations of sweet potato (10,000 and 20,000 plants ha-1) between rows of cassava, planted at 0, 4 and 8 weeks after planting (WAP) cassava, sole cassava and sole sweet potato constituted the main-plots, while four weed control treatments viz pre-emergence application of S-metolachlor+atrazine at 1.16+1.48 kg a.i ha-1 alone (P), S-metolachlor+atrazine at 1.16+1.48 kg a.i ha-1 followed by supplementary hoe weeding at 8WAP (PHW1), three hoe weedings at 4, 8 and 12 WAP (3HW) and a weedy check (0W) were assigned to the sub-plots. Broadleaves, grasses and sedges dominated the field in the ratio of 53.3, 26.2 and 17.5%, respectively averaged over the three years. The major weed species in the study area were Oldenlandia corymbosa > Panicum maximum > Spermacoce verticillata > Lindernia antipoda > Cyperus esculentus > Killinga bulbosa > Charmaecrista rotundifolia > Digitaria horizontalis. Apart from weed seedling emergence, the results indicated significant differences between cropping patterns. Intercropping significantly suppressed weed infestation than sole cassava. Cassava intercropped at the same time with sweet potato at 20,000 plant ha-1 (CS200) significantly (P≤0.05) reduced weed density, dry matter as well as the growth and yield of cassava when compared with the sole cassava treatment which gave the lowest weed control. Weed density and dry matter were higher with intercropped sweet potato introduced at 8 WAP at both populations (CS108 and CS208) comparable to sole cassava due to reduced rainfall during the period of sweet potato growth resulting in lower ground cover. Similarly, the highest cassava plant height, leaf area as well as root yields were obtained with sole cassava which did not differ from CS108 and CS208, whereas CS200 had the highest sweet potato ground cover as well as tuber yield. There were statistically significant differences in weed seedling emergence, growth and yield of cassava and sweet potato between the different weed control methods. P and PHW1 significantly suppressed weed seedling emergence up to 6 WAP in the three years of study when compared to weedy check. Three hoe weeding resulted in the best growth and yield of cassava whereas PHW1 gave the best sweet potato growth and yield. The weedy check (0W) and P recorded the poorest weed control and performance of these crops. In general, CS200 combined with PHW1 gave the highest total intercrop yield, benefit-cost, land equivalent ratios and return on investment better than other combinations. Total land saved under this treatment was 24% which could be used for other agricultural purposes. Therefore, under the soil and weather conditions of the experiment, the cropping pattern and weed control method identified for TME 419 cassava production was cassava intercropped with sweet potato at 20,000 plants ha-1 (CS200) combined with S-metolachor+atrazine at 1.16+1.48 kg ai ha-1 followed by one hoe weeding at 8 WAP (PHW1) and is therefore recommended in cassava-sweet potato based intercrop for effective weed control, optimum yield and a good return on investment.
TABLE OF CONTENTS
Title Page i
Declaration ii
Certification iii
Dedication iv
Acknowledgement v
Table of Contents vi
List of Tables xi
List of Figures xiii
List of Plates xiv
Abstract xv
CHAPTER
1: INTRODUCTION 1
1.1 Background
Information 1
1.2 Statement
of Problem and Research Justification 3
1.3 Research
Scope and Objective. 6
CHAPTER
2: LITERATURE REVIEW 7
2.1 The
Origin and Importance of Cassava 7
2.1.1 Brief
historical background of cassava 7
2.1.2 Adaptation
and growth of cassava 8
2.1.3 Classification
of cassava 9
2.1.4 Importance
of cassava 10
2.2 Weeds
Associated With Cassava. 13
2.3 Constraints
in Cassava Production 14
2.4 Weed
Competition in Cassava Farm 16
2.5 Origin
and Importance of Sweet Potato 18
2.6
Effect of Weed Interference on
Growth and Yield of Root and
Tuber
Crops 22
2.7 Weed
Management Strategies in Root and Tuber Crops 23
2.8. Intercropping
and its Effect on Photosynthetically Active Radiation (PAR) 25
2.9 Nigerian
Small-Scale Farmers and Weed Management in Cassava Field. 27
2.9.1 Cultural
weed management 28
2.9.2 Biological
weed management 29
2.9.3 Chemical
weed management. 30
2.9.4 Integrated
weed management 32
CHAPTER
3: MATERIALS AND METHODS 35
3.1 Experimental
Site 35
3.2 Soil
Properties of the Experimental Site 37
3.3 Field
Operations 37
3.4 Experimental
Design and Treatments 38
3.5 Field
Establishment and Maintenance 40
3.5.1 Source
and preparation of planting materials 40
3.5.2 Planting
operations 40
3.5.3 Trial
management 41
3.6 Experimental
Procedures and Data Collection 41
3.6.1 Weed
seedling composition and emergence 41
3.6.2 Weed
density and dry matter assessment 41
3.6.3 Cassava
leaf area 44
3.6.4 Determination
of photosynthetically active radiation (PAR) 45
3.6.5 Cassava
plant height 47
3.6.6 Sweet
potato ground cover rating 47
3.6.7 Crop
yield 49
3.6.7.1 Cassava
root yield 49
3.6.7.2 Sweet potato tuber yield 49
3.6.8 Productivity
assessment. 49
3.6.8.1 Cost
benefit analysis (CBA) 49
3.6.8.2 Land
equivalent ratio (LER) 50
3.6.8.3 Area
time equivalent ratio (ATER) 51
3.7 Statistical
Analysis of Data 51
CHAPTER
4: RESULTS AND DISCUSSION 52
4.1 Results 52
4.1.1 Pre-planting
soil properties of the experimental site 52
4.1.2 Weed
seedling composition and emergence studies 54
4.1.2.1 Weed
composition and relative abundance 54
4.1.2.2 Emergence pattern of major weed species in the
experimental site 57
4.1.2.3 Effect
of cropping pattern and weed control methods on weed
seedling emergence 60
4.1.3 Weed density 63
4.1.3.1 Effect of cropping pattern and weed control
methods on weed density 63
4.1.3.2 Effect
of cropping pattern and weed control methods on cumulative
weed density 67
4.1.4 Weed dry matter 71
4.1.4.1 Effect of cropping pattern and weed control
methods on weed dry matter 71
4.1.4.2 Effect
of cropping pattern and weed control methods on the cumulative
weed dry matter 77
4.1.5 Cassava leaf area 81
4.1.5.1 Effect of cropping pattern and weed control
methods on cassava leaf area 81
4.1.6 Cassava plant height 85
4.1.6.1:Effect
of cropping pattern and weed control methods on cassava plant height 85
4.1.7 Photosynthetically active radiation (par) 87
4.1.7.1 Effect
of cropping pattern and weed control methods on photosynthetically active radiation (PAR) 87
4.1.8 Sweet potato ground cover rating 91
4.1.8.1 Effect
of cropping pattern and weed control methods on Sweet potato
Ground Cover 91
4.1.9 Cassava root yield 95
4.1.9.1 Effect of cropping pattern and weed control
methods on cassava root
yield 95
4.1.10 Sweet potato tuber yield 99
4.1.10.1Effect of cropping pattern and weed control
methods on Sweet potato
fresh tuber yield. 99
4.1.11.
Profitability of weed control methods and different cropping patterns 103
4.1.12 Correlation analysis 106
4.2 Discussions 110
4.2.1 Meteorological and edaphic properties of
the study area 110
4.2.1.1 Meteorological data and soil properties of
the experimental site 110
4.2.2 Weed seedling composition and emergence
studies 111
4.2.2.1 Weed composition and relative abundance 111
4.2.2.2
Emergence pattern of major weed species in the experimental site. 114
4.2.2.3 Effect of cropping pattern and weed control
methods on weed seedling emergence 115
4.2.3
Weed density 116
4.2.3.1 Effect of cropping pattern and weed
control methods on weed density 116
4.2.3.2 Effect of cropping pattern and weed
control methods on cumulative
Weed density 120
4.2.4 Weed dry matter 121
4.2.4.1
Effect of cropping pattern and weed control methods on weed
dry matter 121
4.2.4.2 Effect of cropping pattern and weed
control methods on cumulative
weed dry matter 124
4.2.5
Cassava leaf area (cm2) 126
4.2.5.1 Effect of cropping pattern and weed
control methods on cassava
leaf area 126
4.2.6
Cassava plant height 128
4.2.6.1
Effect of cropping pattern and weed control methods on cassava plant
height 128
4.2.7
Photosynthetically active radiation (par) 129
4.2.7.1
Effect of cropping pattern and weed control methods on
photosynthetically active
radiation (PAR) 129
4.2.8
Sweet potato ground cover rating 132
4.2.8.1
Effect of cropping pattern and weed control methods on Sweet potato
ground cover 132
4.2.9
Cassava root yield 134
4.2.9.1
Effect of cropping pattern and weed control methods on cassava
root yield 134
4.2.10
Sweet potato tuber yield 137
4.2.10.1Effect of cropping pattern and weed control
methods on Sweet potato
fresh tuber yield. 137
4.2.11 Return
on investment of different cropping patterns and weed control methods 139
4.2.12 Correlation
analysis 141
CHAPTER
5: CONCLUSION AND RECOMMENDATIONS 142
5.1 Conclusion 142
5.2 Recommendations 147
References
Appendices
LIST
OF TABLES
3.1: Monthly
and average annual rainfall (mm) at, Amakama, Abia State
during
the cropping seasons. 36
3.2: Main
and Sub Plot Treatments 39
3.3: Ground
cover scale of sweet potato at Amakama, Nigeria. 48
4.1: Physical
and chemical properties of the soil at the experimental site in
during
2015, 2016 and 2017 cropping seasons. 53
4.2: Weed
species composition and abundance at the experimental field in 2015,
2016 and 2017 cropping seasons. 55
4.3: Effect
of cropping pattern and weed control methods on weed density in
2015,
2016 and 2017 cropping seasons. 64
4.4: Interactive
effect of cropping pattern and weed control methods on
weed
density at 10 MAP in 2015, 2016 and 2017 cropping seasons. 66
4.5: Effect
of cropping pattern and weed control methods on Cumulative weeds
density
at 10 MAP in 2015, 2016 and 2017 cropping seasons 68
4.6: Interactive effect of cropping pattern and
weed control methods on
cumulative
weed density in 2015, 2016 and 2017 cropping season. 70
4.7: Effect
of cropping pattern and weed control methods on weed dry matter
in 2015, 2016 and 2017 cropping
seasons. 72
4.8: Interactive
effect of cropping pattern and weed control methods on weed
dry matter at 8 WAP in 2015, 2016
and 2017 cropping seasons. 74
4.9: Interactive
effect of cropping pattern and weed control methods on
weed
dry matter at 12 WAP in 2015, 2016 and 2017 cropping season. 75
4.10: Interactive effect of cropping pattern and
weed control methods on weed
dry matter at 10 MAP in 2015, 2016
and 2017 cropping seasons. 76
4.11: Effect
of cropping pattern and weed control methods on Cumulative weed dry matter at 10 MAP in
2015, 2016 and 2017 cropping seasons. 78
4.12: Interactive
effect of cropping pattern and weed control methods on
cumulative
weed dry matterin 2015, 2016 and 2017 cropping seasons. 80
4.13. The
effect of cropping pattern and weed control methods on Cassava
Leaf
area at 16WAP in 2015, 2016 and 2017 cropping seasons. 82
4.14: Interactive
effect of cropping pattern and weed control methods on
cassava
leaf area at 16 WAP in 2015, 2016 and 2017 cropping seasons. 84
4.15: Effect
of cropping pattern and weed control methods on Cassava
plant
height in 2015, 2016 and 2017 at Amakama. 86
4.16: Effect
of cropping pattern and weed control methods on
Photosynthetically
active radiation (PAR) in 2015, 2016 and 2017 at Amakama. 88
4.17: Interactive
effect of cropping pattern and weed control methods on
PAR
at 16 WAP in 2015, 2016 and 2017 at Amakama. 90
4.18: Effect
of cropping pattern and weed control methods on Sweet potato ground cover in 2015, 2016 and
2017 cropping season. 92
4.19: Interactive
effect of cropping pattern and weed control methods on
Sweet potato ground cover at 16 WAP
in 2015, 2016 and 2017 cropping
season. 94
4.20: Effect
of cropping pattern and weed control methods on Cassava yield at 10MAP in 2015, 2016 and 2017
cropping season. 96
4.21: Interactive
effect of cropping pattern and weed control methods on
Cassava
yield at 10MAP in 2015, 2016 and 2017 cropping season. 98
4.22: The
effect of cropping pattern and weed control methods on Sweet
potato
yield in 2015, 2016 and 2017 cropping season. 100
4.23: Interactive
effect of cropping pattern and weed control methods on
Sweet
potato yield at 10MAP in 2015, 2016 and 2017 cropping season .102
4.24: Effect
of intercropping on yields of cassava and sweet potato and return on investment in 2017 cropping season. 104
4.25: Effect of cropping pattern and weed control
methods on cassava/sweet
Potato
net income (N) in 2015, 2016 and 2017 cropping season. 105
4.26: Pearson’s
correlation coefficient (r) among weed density, drymatter,
PAR,
cassava height, leaf area, yield, sweet potato yield and ground cover rating in 2015 cropping season. 107
4.27: Pearson’s
correlation coefficient (r) among Weed density, drymatter, PAR, cassava height, leaf
area, yield, sweet potato yield and ground cover rating in 2016 cropping season. 108
4. 28: Pearson’s correlation coefficient (r) among
weed density, drymatter, PAR,
cassava
height, leaf area, yield, sweet potato yield and ground cover
rating in 2017 cropping season 109
LIST
OF FIGURES
3.1 Field
Layout 39
4.1: Weed
population during the 2015, 2016 and 2017 cropping seasons.
Vertical
lines represent standard error bar 56
4.2: Emergence
of grasses broadleaves and sedges in 2015, 2016 and 2017 cropping seasons. Vertical lines
represent standard error bar. 56
4.3: Emergence pattern of dominant weed species
at Amakama, during
the
2015, 2016 and 2017 cropping seasons. 58
4.4: Effect
of cropping pattern on weed seedling emergence patterns in
2015, 2016 and 2017 cropping
seasons. Vertical lines represent LSD
bar. 61
4.5: Effect
of weed control methods on weed seedling emergence patterns in 2015, 2016 and 2017
cropping seasons. Vertical lines represent
LSD bar. 62
LIST
OF PLATES
3.1 (a): Digital
sensitive balance 43
3.1 (b): Electrical
oven drier 43
3.2: A
quantum light meter 46
CHAPTER 1
INTRODUCTION
1.1 BACKGROUND
INFORMATION
The
interest and activities of man are being hampered by the hazards caused by
weed. They interfere with human activities or in some ways intrude upon human
welfare. This is the notion of weed that has evolved with man and within the
context of their food production needs. In tropical agriculture, weeds are most
underestimated as a pest. They have influence on human social action more than
other crop pests (Akobundu, 1987).
Though hazardous to man’s activities, weeds may however be useful as
food or medicine for him and his livestock. Portulaca
oleracea and Talinum triangulare are
examples of useful weeds to humans among many others (Baker, 1974).
Furthermore, weeds serve as soil cover to prevent soil erosion and to recycle
nutrients to the soil in fallow areas. Conversely, various crop plants which
grow as volunteer in other crop areas, are rightly considered as weeds.
About
1800 weed species are estimated to cause serious economic damage or losses to
crop production, and about 300 of these weed species are responsible for the
serious economic loss in cultivated crops throughout the world (Kasasian,
1986). Farmers in the tropics spend more of their time weeding than any other
farming activity (Labarada and Parker, 1975). Majority of the tropical farmers
use hand/hoe weeding in the control of weeds (Akobundu, 1980a). The drudgery
associated with this makes traditional farming unattractive and uneconomical,
particularly by the younger generation of farmers because weed limits the area
of land that can be cultivated. Traditional weed control is labour intensive,
weed infestation is heavy and its reinfestation and growth are rapid allowing
no breathing space for the farmer (Doll, 1977; Akinpelu et al., 2006). Weeds are ready to survive in the face of obstacles
(Akobundu, 1987). These obstacles include herbicides as well as tillage and
crop husbandry practices routinely used to minimize weed competition. This is
attributed to the fact that weeds possess adaptive features such as the ability
to produce large quantities of seed, seed dormancy, periodicity of seed
germination and short lifespan. Crop mimicry by weed is an example of the
extent to which weeds have adapted themselves to survive in such frequently
disturbed sites as farmlands (Soerjani, 1970).
Weed
interference and competition reduces yield and yield component of crops such as
cob weight, tuber number etc (Ahmed and Moody, 1980). These yield reductions
are brought about by competition with crops for growth resources such as light,
soil moisture and nutrients which are in limited supply. Weed control methods
in use are usually labour intensive and the reduction in crop yield is partly
due to early weed interference. Donald (1963) stated that competition occurs
when two or more organisms seek a common resource whose supply is less than the
combined demand of such individuals in that habitat. Reisser (1969) in a review
of competitive relationship among herbaceous grassland plants considered
competition to be applicable to the short term and long-term hardship that
results when organisms live close to one another. He considered the use of the
term interference more appropriate to competition by plants growing near enough
to undergo stress. Interference is the detrimental effect of one plant specie
to another resulting from their interactions with each other (Akobundu, 1987).
Interference includes both competition and allelopathy (Trenbath, 1976). The
interactions of these species, sharing the same environment, therefore include
competition and ammensalism. Ammensalism refers to the interaction in which
growth of one of the organisms (plant) is depressed while the other is
unaffected. In weed–crop interaction, both species are affected and therefore
seen as competition and not ammensalism although emphasis is laid on the
depressive effect of weed on crops while ignoring the effect of crops on weeds.
Under competitive condition, the individual organisms or component strive to
suppress each other’s presence so as to secure for themselves a sufficient
share of the micro environmental growth resources. The critical competitive
period between weeds and crops must be defined for each crop–weed association
and in each region, and every effort should be made to control weed at this
time (Akobundu, 1987).
1.2. STATEMENT OF PROBLEM
AND RESEARCH JUSTIFICATION
Cassava
susceptibility to weed interference is most intense during the first 3 – 4 months
after planting (MAP) and if weed growth is left uncontrolled at this critical
point, it can lead to about 75 – 95 percent reduction in yield (Onochie, 1975,
Chikoye and Ekeleme, 2001). Cassava competes well with weeds once its canopy
has fully been formed. However, its ability to compete with weeds depends to
some extent how long the crop stays weed free after planting before the canopy
covers the ground. Good shading of the ground is obtained in an intercropping
system by growing crops with different architecture. The reason for practicing
mixed cropping by farmers include the production of higher total yield from a
given area of land, insurance against crop failure, reduction in the levels of
insect pests, diseases and weeds and better use of growth resources among
others (Okpara and Omaliko, 1995; Okigbo and Greenland, 1976; Njoku and Muoneke,
2008; Isoken, 2000; Fujita and Offosu-Budu, 1996). According to Akobundu
(1980a) and Enyi (1973), one benefit of intercropping is the ability to
suppress weed better than a sole crop. This is due to the fact that the
canopies of the intercrop system provide more complete ground cover.
The
use of low growing crops has been reported to reduce weed growth in crops
(Taiwo and Ekeleme, 2008; Okeleye et al.,
1999; Moody and Ezumah, 1974; Imeokparia, 1999; Enej iet al., 1995; Bentilan and Hardwood, 1973). Farmers in the tropics
often adopt hoe weeding, thrice in cassava-based intercrop (Umanah, 2005). This
approach is costly, cumbersome and unreliable (Lavabare, 1991). Akobundu (1987)
showed that both sweet potato and egusi melon are good substitute for repeated hand
weeding in maize/cassava, maize/yam and maize/yam/cassava intercropping
systems. In addition to smothering weeds, these low growing crops reduce direct
impact of raindrops on soil surface. Unanma and Ene (1984) reported that
intercropping cassava with maize reduced the critical period of weed
interference from 3 – 12 WAP in sole crop to 3 – 8 WAP in the intercrop. Eneji et al. (1995) also reported that sweet
potato whether grown sole or intercropped suppressed weed due to its early
ground coverage. Also, sweet potato cover at 10,000 plants ha-1 was
reported to be effective in suppressing speargrass in soybean (Taiwo and
Ekeleme, 2008).
The
use of herbicides is perhaps the most economically viable option of weed
control in large hectarage of cassava cultivation, but it must be combined with
other agronomic or management practices that would enhance the ability of
cassava to compete with the weeds (Ekeleme, 2005). These management practices
include combining herbicide application with hand/hoe weeding and intercropping
among others. This is because most of the existing pre-emergence herbicides
have exhibited unsatisfactory weed control in Nigeria due to the narrow
spectrum of weeds controlled and their short persistence (Akinyemiju, 1992).
For example, Akinyemiju (1992) noted that primextra, a formulated mixture of
atrazine (3.0 kg/ha) and metolachlor (3.6 kg/ha) controlled weeds for only 4 WAP.
Similarly, Ekpo et al. (2012)
reported that the same herbicide applied without supplementary weeding did not sufficiently
control weeds up to 12 WAP. Metolachlor belongs to the herbicide chemical group
known as the Acetamides while atrazine belongs to the Triazines. Acetamides are
easily degraded by microbes and therefore can only provide weed control for
10-14 weeks (Rao, 1999). The half life of Metolachlor in surface soils from
field experiment is 13.7 days (Weller and Owen, 2016). Triazines are very
soluble in water and easily absorbed by the roots of the emerging weed
seedlings and move appoplastically to the leaves and shoots (Weller and Owen,
2016; Rao, 1999). They are also degraded by microbes which contribute to their
short persistence in the soil for prolonged weed seedling depression. Ekpo et al.(2012) however, observed that
metolachlor (1.5 kg. a.i. ha-1) plus cowpea (80,000 plants ha-1)
and one hoe weeding controlled broadleaf plants, grasses and sedges
satisfactorily and significantly enhanced both cassava and maize growth and
also cassava tuber yield. There
is need to reduce the herbicide rate in order to cut cost and mitigate the
problems of environmental build up of herbicide residue and reduce the drudgery
associated with hand/hoe weeding.
Cassava is usually intercropped with other staples
which are mainly short-season and early-maturing crops in most traditional
cropping systems. They include sweet potato, yam, cocoyam, maize, ‘egusi’
melon, and cowpea. Okigbo and Greenland (1976) estimated that about 50% of the
cassava grown in tropical Africa is intercropped with cereals, legumes, leafy
vegetables and fruits as well as tree crops. Low
growing leguminous crops have the potential to improve the soil fertility
status, farmers’ income and are beneficial to crops in association (Ogunremi,
2005). Anuebunwa (2000) reported early weed suppression by egusi in
cassava/yam/egusi/sweet potato intercrop. He further reported that the yield of
the component crops was similar except cassava. The yield of yam and cassava
were highest when sweet potato was introduced at 10 WAP than with 2 hand
weeding and it also gave higher monetary revenue of all the other component
crops combined as well as a higher net benefit. Ijoyah et al. (2012) reported that intercropping cassava and sweet potato
was highly complementary and most suitable in mixture when 30 cm cassava
cutting length was used.
Weed
control in intercropping systems has posed a great threat to yields of
component crops. Earlier study by Chikoye et
al. (2000) showed that planting of cover crops with food crops
simultaneously has a good potential for reducing cost of weed control and
production. However, one of the problems of weed control in intercropping
systems is not being able to satisfy the needs of all crops in the
intercropping systems (Akobundu, 1987), hence the need to combine two or more
weed control methods at lower input. According to Okpara et al. (2004), the maximum productivity in intercrop could be
achieved when inter and intra competitions are minimal for growth limiting
factors and the density of each crop adjusted to minimize competition between
them.
1.3. RESEARCH SCOPE AND
OBJECTIVE.
There
is paucity of information on integrated weed management system involving time
of planting and population of sweet potato, reduced rate of herbicide and hoe
weeding in cassava-sweet potato-based intercrop system. Therefore, the
objectives of this study were to:
1. Evaluate
the effect of time of planting, population of sweet potato and weed control
methods on weed seedling emergence pattern.
2. Evaluate
the effect of time of planting, population of sweet potato and weed control
methods on weed density and dry matter.
3. Evaluate
the effect of time of planting, population of sweet potato and weed control
methods on growth and yield of sweet potato and cassava.
4. Evaluate
the economics/productivity potential of cassava and sweet potato complemented
with different weed methods in cassava/sweet potato intercrop.
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