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DEVELOPMENT AND APPRAISAL OF ECONOMICAL AND SUSTAINABLE APPROACH FOR WEED MANAGEMENT IN DRILL SEEDED

AEROBIC RICE (Oryza sativa L.)

BY

MUHAMMAD SAQIB M.Sc. (Hons.) Agriculture

A thesis submitted in partial fulfillment of the requirements for the degree of

DOCTOR OF PHILOSOPHY

IN

AGRONOMY

DEPARTMENT OF AGRONOMY

FACULTY OF AGRICULTURE

UNIVERSITY OF AGRICULTURE, FAISALABAD

PAKISTAN

2013

To, The Controller of Examinations,

University of Agriculture,

Faisalabad.

“We the supervisory committee, certify that the contents and form of thesis

submitted by Mr. Muhammad Saqib, Regd. No. 2001-ag-2563, have been found

satisfactory and recommend that it be processed for evaluation by External Examiner(s)

for the award of degree.”

SUPERVISORY COMMITTEE

1. Chairman: ___________________

Dr. Nadeem Akbar

2. Member: ___________________

Prof. Dr. Ehsanullah

3. Member: ___________________

Prof. Dr. Abdul Ghafoor

Declaration

I hereby declare that contents of the thesis, “Development and appraisal

of economical and sustainable approach for weed management in drill

seeded aerobic rice (Oryza sativa L.)” are product of my own research

and no part has been copied from any published source (except the

references, standard mathematical or genetic models/equations/formulae

/protocols etc.). I further declare that this work has not been submitted

for award of any other diploma/degree. The university may take action if

the information provided is found inaccurate at any stage. (In case of any

default, the scholar will be proceeded against as per HEC plagiarism

policy).

MUHAMMAD SAQIB

DEDICATED

TO

HOLY PROPHET MUHAMMAD

(Peace Be Upon Him)

The personality

for whom

world was created

i

ACKNOWLEDGEMENTS

All acclamation, appreciation and praise for the ALMIGHTY ALLAH, the most

gracious and compassionate, whose blessing and exaltation flourished my thought and

thrived my ambition to have the cherished fruit of my modest efforts in the form of this

manuscript from the blooming spring of blossoming knowledge.

My special praises for the HOLY PROPHET MUHAMMAD (Peace Be Upon Him) who is

forever a torch of guidance for the entire humanity.

With a proud sense of gratitude, I acknowledge that this manuscript has found this shape

under the kind supervision, inspiring guidance and sympathetic attitude of Dr. Nadeem Akbar,

Asstt. Professor, Department of Agronomy, University of Agriculture, Faisalabad, who benevolently

extended all possible help for the smooth execution of this humble presentation.

I offer my great sense of gratitude to Dr. Ehsanullah, Professor, Department of Agronomy,

University of Agriculture, Faisalabad, for providing valuable suggestions, competent guidance and

boosting up my morale during the conduct of this study.

I am highly indebted to Dr. Abdul Ghafoor, Professor, Institute of Soil and Environmental

Sciences, University of Agriculture, Faisalabad, for his constructive criticism and valuable

suggestions to improve this manuscript.

I shall be missing something if I don’t extend my admiration and appreciation to Mr. Tariq

Masood Qurashi who helped me to increase my abilities of learning.

I am also thankful to my sincere friends Dr. Abdul Ghafar, Dr. Shahzad Ali Shahid

Chatta, Dr. Attiq-ur-Rehman, Adnan Shakir, Imran Ahmad Chishti, Sajja Anjum Sandhu and

Zafar Iqbal who supported me morally with sentiment throughout my research.

Last but not the least gratitude is to be expressed to my affectionate father Muhammad

Iqbal Goraya, my loving mother, my brother Muhammad Asif Iqbal Goraya, my beloved sister

and my wife for their love, patience, inspiration, good wishes and unceasing prayers for me to achieve

higher goals in life.

MUHAMMAD SAQIB

ii

TABLE OF CONTENTS

Chapter No. TITLE

ACKNOWLEDGEMENTS

TABLE OF CONTENTS

LIST OF TABLES

LIST OF FIGURES

LIST OF ABBREVIATIONS

ABSTRACT

Page No.

i

ii

vi

xi

xiv

xv

1 INTRODUCTION 1

2 REVIEW OF LITERATURE 5

2.1 Rice 5

2.1.1 History of domestication and cultivation 5

2.2 Crop establishment methods 6

2.2.1. Flooded rice 6

2.2.2 Aerobic rice 7

2.2.3 Global distribution of direct seeded rice 8

2.2.4 Crop establishment metods of direct seeded rice 9

2.2.4.1 Wet seedining 9

2.2.4.2 Water seeding 9

2.2.4.3 Zero tillage seeding 9

2.2.4.4 Dry seeding 10

2.3 Weeds 10

2.3.1 Effects of weeds on rice 10

2.3.2 Weeds in direct seeded rice 12

2.3.3 Weed control 12

2.3.4 Planning effective control 12

2.4 Weed control methods 13

2.4.1 Cultural control methods 13

2.4.2 Biological weed control methods 13

iii

2.4.3 Problems of biological weed control methods 13

2.4.4 Mannual weed control 14

2.4.5 Problems of Mannual weed control 14

2.4.6 Chemical weed control methods 15

2.4.7 Problems of chemical weed control methods 15

2.4.8 Mechanical weed control 16

3 MATERIALS AND METHODS

3.1 Location of studies 17

3.2 Characterization of Soil 17

3.2.1 Particle size analysis 17

3.2.2 pH of saturated soil paste 17

3.2.3 Soil saturated extract 18

3.2.4 Soil organic matter 18

3.2.5 Electrical conductivity of saturated soil extract 18

3.2.6 Total soluble salts 18

3.2.7 Available phosphorous 19

3.2.8 Extractable potassium 19

3.3 Treatment and layout of experiments 21

3.4 Planting of crop 25

3.4.1 Land preparation 25

3.4.2 Seeding method, planting geometry and fertilizer application 25

3.4.3 Water management 25

3.4.4 Harvesting and threshing 25

3.5 Weed management in experiment I 25

3.6 Weed management in experiment II 25

3.7 Observations 26

3.7.1 Yield related traits 26

3.7.2 Quality parameters 26

3.7.3 Growth parameters 26

3.7.4 Weed parameters 27

iv

3.8 Statistical analysis 31

4 REULTS AND DISCUSSION

STUDY-I : COMPARISON OF DIFFERENT WEED

MANAGEMENT STRATEGIES IN DRILL SEEDED

AEROBIC RICE

4.1 Weed biomass of sedges (15 DAS) 32

4.2 Weed biomass of broad leaf weeds (15 DAS) 32





4.7 Total weed biomass (15 DAS) 37



4.10 Plant Height 40

4.11 Total number of tillers 43

4.12 Number of fertile tillers 43

4.13 Number of unfertile tillers 47

4.14 Panicle length 47

4.15 Kernels per panicle 47

4.16 1000-kernel weight 51

4.17 Biological yield 51

4.18 Paddy yield 51

4.19 Straw yield 57

4.20 Harvest Index 57

4.21 Opaque kernels 57

4.22 Abortive kernels 60

4.23 Normal kernels 60

4.24 Sterile spikelets 60

4.25 Leaf area index 62

v

4.26 Crop growth rate 62

4.27 Leaf area duration 62

4.28 Total dry matter 66

4.29 Net assimilation rate 66

4.30 Economic analysis 69

Discussion 73

STUDY-II: EVALUATION OF DIFFERENT INTER

CULTURAL IMPLEMENTS FOR WEED

MANAGEMENT IN DRILL SEEDED AEROBIC RICE










4.40 Plant height 94

4.41 Total number of tillers 97

4.42 Number of fertile tillers 99

4.43 Number of unfertile tillers 101

4.44 Panicle length 103

4.45 Kernels per panicle 103

4.46 1000-kernel weight 106

4.47 Biological yield 108

4.48 Paddy yield 110

4.49 Straw yield 112

4.50 Harvest Index 112

4.51 Opaque kernels 115

vi

4.52 Abortive kernels 117

4.53 Normal kernels 117

4.54 Sterile spikelets 120

4.55 Leaf area index 122

4.56 Crop growth rate 124

4.57 Leaf area duration 124

4.58 Total dry matter 127

4.59 Net assimilation rate 127

4.60 Economic analysis 130

Discussion 135

5 Summary 139

References 144

vii

LIST OF TABLES

Table Title Page

3.1 Physio-chemical analysis of experimental site 19

3.2 Meteorological data during the year 2008 at experimental site 20 3.3 Meteorological data during the year 2009 at experimental site 20 3.4 Weed flora 27 4.1 Effect of different weed management strategies on weed

biomass (45 DAS) 41

4.2 Effect of different weed management strategies on plant height

41

4.3 Effect of different weed management strategies on total number of tillers

44

4.4 Effect of different weed management strategies on number of fertile tillers

44

4.5 Effect of different weed management strategies on number of unfertile tillers

45

4.6 Effect of different weed management strategies on panicle Length

45

4.7 Effect of different weed management strategies on kernels per panicle

48

4.8 Effect of different weed management strategies on 1000 kernel weight

48

4.9 Effect of different weed management strategies on biological yield

52

4.10 Effect of different weed management strategies on paddy yield

52

4.11 Effect of different weed management strategies on straw yield

58

4.12 Effect of different weed management strategies on harvest index

58

4.13 Effect of different weed management strategies on opaque kernels

59

4.14 Effect of different Weed management strategies on abortive kernels

59

4.15 Effect of different weed management strategies on normal kernels

61

4.16 Effect of different weed management strategies on sterile spikelets

61

4.17 Economic analysis 2008 69 4.18 Economic analysis 2009 70 4.19 Dominance analysis 2008 71 4.20 Marginal analysis 2008 71

viii

4.21 Dominance analysis 2009 72 4.22 Marginal analysis 2009 72 4.23 Effect of different weed control implements on weed

biomass at 45 DAS 95

4.24 Effect of different weed control implements on plant height 96 4.25 Effect of different weed control implements on total number

of tillers 98

4.26 Effect of different weed control implements on number of fertile tillers

100

4.27 Effect of different weed control implements on number of unfertile tillers

102

4.28 Effect of different weed control implements on panicle length 104 4.29 Effect of different weed control implements on kernels per

panicle 105

4.30 Effect of different weed control implements on 1000 kernel weight

107

4.31 Effect of different weed control implements on biological yield

109

432 Effect of different weed control implements on paddy yield 111 4.33 Effect of different weed control implements on straw yield 113 4.34 Effect of different weed control implements on harvest index 114 4.35 Effect of different weed control implements opaque kernels 116 4.36 Effect of different weed control implements abortive kernels 118 4.37 Effect of different weed control implements normal kernels 119 4.38 Effect of different weed control implements on sterile

spikelets 121

4.39 Economic analysis 2008 131 4.40 Economic analysis 2009 132 4.41 Marginal analysis 2008 133 4.42 Marginal analysis 2009 134

ix

LIST OF FIGURES Figure Title Page

3.1 Layout plan for experiment-I 22

3.2 Layout plan for experiment-II 24

4.1 Effect of different weed management strategies on weed biomass of sedges and broad leaf weeds at 15 DAS

33


35


36

4.4 Effect of different weed management strategies on total weed biomass at 15 DAS

38


38


39

4.7 Relationship between total weed biomass (45 DAS) and plant height

42

4.8 Relationship between total weed biomass (45 DAS) and fertile tillers

46

4.9 Relationship between total weed biomass (45 DAS) and kernels per panicle

49

4.10 Relationship between total weed biomass (45 DAS) and 1000 kernels weight

50

4.11 Relationship between total weed biomass (45 DAS) and paddy yield

53

4.12 Relationship between number of fertile tillers and paddy yield 54 4.13 Relationship between kernels per panicle and paddy yield 55 4.14 Relationship between 1000 kernel weight and paddy yield 56 4.15 Effect of different weed management strategies on periodic

changes in leaf area index 63

4.16 Effect of different weed management strategies on periodic changes in crop growth rate

64

4.17 Effect of different weed management strategies on cumulative leaf area duration at 105 DAS

65

4.18 Effect of different weed management strategies on total dry matter at 105 DAS

67

4.19 Effect of different weed management strategies on NAR at 105 DAS

68

4.20 Effect of different weed control implements on weed biomass of broad Leaf weeds (15 DAS)

81

4.21 Effect of different weed control implements on weed biomass of sedges (15 DAS)

82

x


84


85


87


89

4.26 Effect of different weed control implements on total weed biomass (15 DAS)

90


92


93

4.29 Effect of different weed control implements on periodic changes in leaf area index

123

4.30 Effect of different weed control implements on periodic changes in crop growth rate

125

4.31 Effect of different weed control implements on cumulative leaf area duration at 105 DAS

126

4.32 Effect of different weed control implements on total dry matter at 105 DAS

128

4.33 Effect of different weed control implements on NAR at 105 DAS

129

xi

LIST OF ABBEREVATIONS

ABBEREVATION DESCRIPTION DAS Days after sowing DSR Direct seeded rice LAI Leaf area index LAD Leaf area duration CGR Crop growth rate TDM Total dry matter NAR Net assimilation rate HI Harvest index LSD Least significant difference Zn Zinc t Ton ha-1 Per hectare cm Centimeter g Gram Fig Figure m-2 Per square meter % percentage @ At the rate of kg Kilogram ppm Parts per million N Nitrogen P Phosphorus K Potassium

xii

ABSTRACT

Traditional rice cultivation by puddling and manual transplanting is a labor intensive activity and

require significant quantities of water and power. The increasing scarcity of water threatens the

sustainability of transplanted rice. In many areas of Asia, transplanting of rice is being replaced

by direct seeding as farmers respond to increased labor cost and decreased water availability but

weed control is one of the major constraints to direct seeding. So, to control weeds in direct

seeded rice studies were designed. Experiments were conducted for two years to develop

sustainable and economical methods for managing weeds in aerobic rice grown by direct-seeding

at Student’s Farm, Department of Agronomy, University of Agriculture, Faisalabad during the

years 2008 and 2009. The first experiment was laid out in RCBD having five weed control

approaches; hand weeding, hoeing (with kasula), inter row cultivation with tine cultivator, inter

row cultivation with spike hoe and chemical control with Nominee 100 SC along with control

(no weeding). Weed dry weight was 300 g m-2, 257 g m-2, 225 g m-2 and 157 g m-2 less in hand

weeding, hoeing tine cultivator and Nominee 100 SC respectively than no weeding. Maximum

fertile tillers were recorded in hand weeding (369.73 m-2) and were followed by hoeing (356.94

m-2) and tine cultivator (346.78 m-2). Hand pulling, hoeing, tine cultivator, Nominee and spike

hoe gave 28, 25, 22, 12 and 6% more number of kernels per panicle respectively. Paddy yield

was 221, 203, 181 and 105% more in hand weeding, hoeing tine cultivator and Nominee 100 SC

respectively than no weeding. Highest net returns (Rs. 56905) were obtained by hand weeding

while highest BCR (1.75) was obtained in tine cultivator. A second experiment was laid out in

split plot design randomizing inter row cultivation implements in main plots and inter row

cultivation frequencies in sub plots. Weed dry weight was 199.16 g m-2 less when tine cultivator

was used at 15, 25, 35 and 45 DAS as compared to weed dry weight in inter row cultivation at15

days after seeding (DAS). More fertile tillers in tine cultivator and spike when used at 15, 25, 35

and 45 DAS were observed. Paddy yield was 159% more when tine cultivator was used at 15,

25, 35 and 45 as compared to paddy yield in inter row cultivation at15 DAS. Tine cultivator gave

maximum net return and BCR when used at 15, 25, 35 and 45 DAS. Tine cultivator gave

maximum net return and BCR when used at 15, 25, 35 and 45 DAS. Both experiments were

replicated thrice. Net plot size was 3.0 m x 6.0 m in both experiments. Weed control by tine

cultivator displayed excellent rice yields when repeated cultivation was done, and with the

reduced labor inputs compared to hand weeding and hoeing, is a viable and economical method.

1

CHAPTER 1

INTRODUCTION

Rice (Oryza sativa L.) is a principal source of food for more than half of the world

population, especially in South and Southeast Asia and Latin America. Rice is the third largest

crop after wheat and cotton and second major grain crop of Pakistan. It accounts for 6.4 % of

value added in agriculture and 0.9 % in GDP of Pakistan. In Pakistan, it is grown on an area of

about 2.88 m ha and its total production is 4.82 million tons with an average paddy yield of 2.03

t ha-1. Rice is food as well as contributing 20 % in foreign exchange earnings of Pakistan (GOP,

2011).

Rice is cultivated in many parts of the world in different ways; transplanted flooded rice,

alternate wetting and drying, rice on raised beds and aerobic rice. The main cropping differences

are between aerobic and puddled rice. Seventy five percent of Asian rice is produced in irrigated

puddled fields with generally high irrigation requirements to sustain sub merged conditions for

most of the growing season (Bouman and Toung, 2003). In Pakistan rice is grown under diverse

climatic and edaphic conditions. Basmati cultivars (Super Basmati, Basmati Pak and Basmati

385) dominate in the traditional rice tract of the Punjab known as “Kalar” tract. At high altitudes

like Swat where temperature is low, temperate Japonica rice (IR-6, Shadab and Shua-92) is

grown. In the South of Khyber Pakhtoon Kha, Sindh and Baluchistan coarse rice (IR-6, IR-9,

DR-82 and DR-83) is grown. Rice is also grown on, ‘salt affected and water logged soils’ such

soils are generally unfit for the production of other agricultural crops (Funakawa et al., 2000).

Water is the major factor limiting crop production in many parts of the world. However,

concerns are increasing about its future availability even in areas where water for irrigation is

currently plentiful (Rijsberman, 2006). Bouman and Tuong (2003) reported that in 2025, 15 out

of 75 m ha of Asian transplanted rice crop will experience water shortage. Water shortage is a

great threat to Pakistan agriculture due to huge exploitation of available water. Agriculture

consumes 70 % of the world water use (IWMI, 2007). Owing to some irrigation water rice is

mostly grown by transplanting method. In this method field is puddled before rice transplantation

then water is impounded. This continuous flooding requires lot of water and high labor (Bhushan

et al., 2007). Pakistan is confronting severe canal water shortage due to lack of interest for the

construction of new surface reservoirs. Surface water availability in 2005-2006 was 100.9 MAF

2

which decreased to 93.3 MAF in 2009-2010 (GOP, 2010). Due to constant decrease in

availability of irrigation water, it seems very difficult to grow rice with transplanting method in

future.

Paddy yield of Pakistan is either stagnant or declining, mostly due to late sowing, low

availability of water, nutrient imbalances, sub-optimum plant population, high infestation of

weeds and labor shortage in transplanted rice (Mann and Ashraf, 2001). Rapid economic

development has great influence on agricultural labor availability as it promotes rural labor

migration to urban areas for higher income from secondary industries resulting labor shortage in

rural area (Habito and Briones, 2005). Technological innovation is needed to allocate less labor

input for production of rice. Agricultural mechanization would be one possibility for labor-

saving. The alternative way is to partly shift from traditional transplanting to more labor and

water saving methods for rice production like alternate wetting and drying, rice on raised beds

and aerobic rice.

Aerobic rice is a good alternative of transplanting. Aerobic rice refers to the process of

establishing rice crop from seeds sown in the field rather than by transplanting seedlings (Rao et

al., 2007). This type of rice is also known as direct seeded rice (DSR). Direct seeded rice avoids

puddling and continuous wet soil conditions and thus decreases considerably the overall water

demand for rice culture while yield potential is equivalent to the transplanted rice (Awan et al.,

1989). In South Asia, direct seeded rice is being practiced in terraces on sloppy lands of

Bangladesh and along Western Himalayan region of India (Gupta et al., 2007). Direct seeding

with subsequent saturated conditions on flat land decreases the amount of water required during

land preparation (Bouman and Toung, 2003). Water saving of 35–57 % has been reported for

aerobic rice sown into non-puddled soil as compared with continuously flooded (up to 5 cm)

transplanted rice (Bhushan et al., 2007). Bouman and Toung (2003) also found that aerobic rice

can reduce water use by as much 50 % while maintaining a moderately high yield as compared

with transplanted rice. The DSR required 66 % less labor than transplanted rice (Ho and Romli,

2000).

Weeds pose a serious threat to the direct seeded rice crop by competing for nutrients,

light, space and moisture throughout the growing season. Ramzan (2004) reported up to 74 %

3

yield reduction in direct seeded rice due to weeds. Aerobic soil conditions, dry-tillage practices

and alternate wetting and drying are favorable for germination and growth of highly competitive

weeds, causing grain yield losses up to 91 % (Elliot et al., 1984). Choubey et al. (2001) and

Bahar and Singh (2004) also reported that weeds can decrease yield of DSR from 75 to 100 %. If

weeding is delayed beyond 20 days after emergence, permanent damage may be done to rice

crop. During early establishment, weeds make 20-30 % of their growth while the crop makes 2-3

% of its growth (Moody, 1990). The optimum time at which crop must be free of the adverse

effect of weeds is referred to as the critical period of weed competition. Almost all the annual

crops are susceptible to weed competition during the early stage of development, particularly

within the first one-third to one-half of the crop life cycle (Mercado, 1979). Chauhan and

Johnson (2011) concluded that the critical period for controlling of rice weeds in DSR was

between 14 - 41 days after sowing (DAS). So, in critical period rice must be free from weeds for

better production.

In the light of above discussion it is concluded that an effective, economical and timely

weed control strategy must be developed for direct seeded rice. With the availability of proper

weed management technology, it is possible to raise the productivity of direct seeded rice. Weeds

in direct sown rice can be controlled by various methods. Weeds could be controlled by hand

weeding, chemical and mechanical methods. Weeds are manually removed or uprooted in hand

weeding. Hand weeding is commonly practiced against weeds on small-scale rice farms

(Adesina et al., 1994). Farmers in Africa use family labor to control weeds in DSR, weeding

starts at 15-30 DAS and continue for many days depending on the type of weeds (Oteng and

Sant’Anna, 1999). Similarly, in Cambodia hand weeding is done at least twice and commonly

thrice (Makara et al., 2001). Manual weeding can control weeds but it is laborious and time

consuming (Stessens, 2002). Herbicides provide effective weed management in DSR (Azmi et

al., 2005) using as pre emergence or post emergence (Rao et al., 2007). Although chemical

control provides a considerable weed control on DSR but availability of required weedicides is

limited in Pakistan. Secondly weed resistance to various chemicals is also a problem which may

be crested in future. Another way to control weeds in direct seeded rice is use of manually or

mechanically operated implements. In line sown DSR weeds can be controlled effectively by the

use of different inter row implements as reported by Islam et al. (2004). Remington and Posner

(2000) demonstrated effective weed control in DSR using a mechanical weeder. Fazlolallh et al.

4

(2001) an Iranian scientist compared two mechanical weeders in rice; mechanical weeder with

engine power and mechanical weeder without engine power both provided effective and

economical weed control resulting in good yield.

The purpose of this study is to develop and test economical weed control methods that

would allow earlier and more rapid weeding in direct seeded rice. These options included: row

seeding rice with automatic drill to maintain row to row distance, mechanical inter row

cultivation with manual drawn equipment and weed control with herbicides. Keeping in view the

above facts this study was planned with the following objectives.

1. To assess the production potential of direct seeded rice.

2. Assessing the performance of different implements for inter-row weed control.

3. To identify the most suitable and economical weed control method.

4. Comparison of different weed management strategies and their impact on growth and

yield parameters of direct seeded rice.

5

CHAPTER 2

REVIEW OF LITERATURE

On the basis of studies conducted on various aspects of aerobic rice cultivation system, this

chapter is divided into following sections.

1. Rice

2. Crop establishment methods of rice

3. Weeds

4. Methods of weed control

2.1 Rice

Rice is monocot plant Oryza sativa (Asian rice) or Oryza glaberrima (African rice). Rice

belongs to the genus Oryza of the sub tribe oryzineae in the family Gramineae. Its genus Oryza

comprises 25 accepted species, of which 23 are wild and two (Oryza sativa and Oryza

glaberrima) are cultivated. All the rice varieties of Europe, America and Asia belong to the

specie Oryza sativa, while many of the cultivated varieties of West Africa belong to the specie

Oryza glaberrima. Rice is used as staple food for more than half of the world (Chauhan and

Johnson, 2011). About 90 % of rice is produced in the South Asian countries on an area of

153.25 m ha with an average annual production of about 610 million tons, extending from the

Indo-Pak subcontinent to Japan (IRRI, 2004).

2.1.1 History of domestication and cultivation

The commonly accepted view is that rice was first domesticated in the region of the

Yangtze River valley in China (Vaughan et al., 2008). Morphological studies of rice phytoliths

from the Diaotonghuan archaeological site show the transition from cultivation of wild rice to

domesticated rice. Changes in the morphology of Diaotonghuan phytoliths dating from 10,000-

8,000 years before present show that rice had by this time been domesticated (Mac Neish and

Libby, 1995). Soon afterwards, the two major varieties of Indica and Japonica/Sinica rice were

grown in Central China (Harris, 1996). In the late 3rd millennium before Christ (BC), there was

a rapid expansion of rice cultivation into mainland of Southeast Asia and westwards across India

and Nepal (Harris, 1996).

6

Korean archaeologists claimed to have discovered the world's oldest domesticated rice

(David, 2003). Although combined effort by the Stanford University, New York University,

Washington University in St. Louis, and Purdue University has provided the strongest evidence

yet there is only one origin of domesticated rice, in the Yangtze Valley of China (Molina et al.,

2011).

Thirty seven archeological sites have shown traces of rice cultivation in ancient time in

Indo-Pak subcontinent. These sites include Mohenjodaro in Pakistan, Gujrat, Lohal, Rangpur and

Uttar Pradesh in India (Chang, 1967). The earliest remains of rice in the Indian subcontinent

have been found in the Indo-Gangetic Plain and date from 7000-6000 BC though the earliest

widely accepted date for cultivated rice is placed at around 3000–2500 BC with findings in

regions belonging to the Indus Valley Civilization (Pokharia et al., 2009). It then spread to all the

fertile alluvial plains watered by rivers. Cultivation and cooking methods are thought to have

spread to the west rapidly and by medieval times, southern Europe saw the introduction of rice as

a hearty grain. According to Zohary and Maria (2000), Oryza sativa was recovered from a grave

at Susa in Iran (dated to the 1st century AD) at one end of the ancient world, another

domestication of rice in the South Asia.

2.2 Crop establishment methods

The production system of Asia is undergoing adjustments in response to rising scarcity of

land, water and labor. A major adjustment can be expected in the method of crop establishment.

Major determinants of farmer’s choice of crop establishment method are rainfall pattern,

sufficient water supply, weed incidence and field elevation. Availability of labor and power for

land preparation and wage rates were found to be among the major economic factors for the

choice of crop establishment method (Pandey and Velasco, 1999). Rice is grown by two methods

as discussed in the following sections.

2.2.1 Flooded rice

Commonly flooded rice is grown throughout the world. In this method first nursery plants

are grown which are then transplanted in the leveled and puddled field for establishment of crop.

This transplantation of rice seedling may be manual or by machines. Traditional method of

transplantation requires lot of labor and continuous water inputs. Shortage of labor at this critical

7

stage often results in low production and increases labor costs. Rice has lower water productivity

than some other cereal crops (Bhuiyan, 1992). Puddling helps to decrease percolation losses and

control of weeds. However, the puddling process results in subsurface compaction (Kukal and

Aggarwal, 2003), which impedes the growth and yield of succeeding wheat crop. Puddling also

affects soil health due to mechanical dispersion of soil particles and making tillage operations

difficult, requiring more energy in succeeding crops such as wheat (Singh et al., 2003). Water in

conventional rice crop represents a major and necessary production cost for the growers.

Farmers in many rice growing areas have restricted availability of irrigation water and in

future it is predicted that in Asia, 17 m ha of irrigated rice areas may experience ‘‘physical water

scarcity’’ and 22 million ha may have ‘‘economic water scarcity’’ (Toung and Bouman, 2003).

Thus water scarcity threatens the sustainability of irrigated rice ecosystems since it may no

longer be feasible for farmers to undertake wet cultivation and flood fields to ensure good crop

growth and control weeds (Johnson and Mortimer, 2005). The increasing cost of labor threatens

the sustainability of transplanted rice within the rice wheat system of the Indo Gagnetic Plains.

2.2.2 Aerobic rice

One of the strategies to combat water shortage is the system of aerobic or direct seeded

rice. Aerobic rice production consists of sowing seeds in dry soils. Decreased water input, low

labor requirement and timely sowing can be listed as possible benefits of the DSR (Bhushan et

al., 2007). In aerobic or DSR, generally cultivars could have high yield, input-responsive and

could adapt to mild to medium water stress (Bouman et al., 2005). Especially on coarse textured

soils with high seepage and percolation rates, aerobic rice has an advantage over systems that

include saturated or partially flooded soil conditions (Wang et al., 2002). Aerobic rice systems

have been developed since the mid-eighties and aerobic rice is now grown commercially in many

countries of the world especially in Brazil and Northern China (Wang et al., 2002).

According to Guimaraes and Stone (2000), aerobic rice yields similar to that from

transplanted. Direct seeding is cost effective, can save water through earlier rice crop

establishment and allows early sowing of wheat (Ladha et al., 2003; Singh et al., 2003). Aerobic

rice cultivation is a new technology that suits to high yielding varieties with a much lower water

input than that required for traditional rice cultivation. A commercial cropping system based on

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aerobic rice has spread widely in Brazil as a result of the development of improved high yielding

varieties (Pinhiero et al., 2006).

Paddy yield of 5-6 t ha-1 can be achieved in the aerobic rice system (George et al., 2002).

By limiting water losses through seepage, percolation and evaporation, aerobic rice limit total

water use by 27-51 % as compared with transplanted rice crop (Bouman et al., 2005). Similar

observations were reported by Wang et al. (2002) that aerobic rice system can decrease water

application by 44 % compared to the conventionally transplanted rice system, mostly through

decreasing percolation, seepage and evaporation losses, while maintaining yield at a satisfactory

level.

The water requirement of aerobic rice is potentially much less than that of flooded rice

because of: (1) the absence of water use for wet land preparation (puddling), (2) the absence of

continuous seepage and (3) the absence of evaporation losses from the pounded water layer

(Bouman et al., 2005). The potential water saving at field level when rice can be grown as an

upland crop are large, especially on soils with high seepage and percolation rates (Bouman

Toung, 2001). Properly managed aerobic rice results in reasonable yields as Tabbal et al. (2002)

reported that DSR yielded the same as transplanted rice while water inputs were decreased by 35

% and water productivity increased by 45 % compared with that under flooded conditions.

2.2.3 Global distribution of direct seeded rice

Growing of direct seeded rice varies broadly across countries and regions. DSR is planted

either in a dry seeded or wet seeded system in the United States (Gianessi et. al., 2002), Australia

and Europe (Ferrero and Nguyen, 2004). Pandey and Velasco (2002) reported that direct seeding

was rising rapidly in Asia, with 21-22 % of the total rice area being dry seeded or wet seeded.

Dry direct seeding in India is extensively practiced in rain fed lowlands, uplands and

flood prone areas, while wet seeding is a common practice in irrigated areas (Mishra et. al.,

2005). In Vietnam, especially in the Mekong Delta, rice is sown wet seeded and broadcasting is

common practice (Luat, 2000). Kim et al. (2001) reported that 11 % of the total rice was direct

seeded in Korea, dry seeding was 6.4% and wet seeding 4.7 %.

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In the northern provinces of Cambodia, in wet season, 80-90 % of rice fields are dry

direct seeded (CIAP, 1998). In Philippine both dry and wet seeding is commonly practiced (De

Dios et. al., 2005). In Thailand, the rain fed rice area is dry direct seeded, whereas irrigated area

in the Central Plain is mostly wet seeded (Azmi et al., 2005). In Malaysia, wet seeding is favored

but is encouraged only where efficient water management is possible (Azmi et al., 2005). In

Northern and North Eastern regions of China rice seeded directly into aerobic non puddled soils,

area under direct seeding in these regions is 80,000 and 60,000 ha, respectively (Xie et al.,

2005).

2.2.4 Crop establishment methods of direct seeded rice

Farmers usually adopt four types of crop establishment methods in relation to

hydrological conditions for direct seeding of rice.

2.2.4.1 Wet seeding

Rice seeds are soaked for 24 hrs and incubated from 24 to 36 hrs. Pre-germinated seeds

are then sown on to the soil surface. Typically water is reintroduced into fields for weed

suppression 7-10 days after sowing (DAS). Weed infestation is usually lower in wet seeded rice

than in dry-seeded and zero-tilled rice (Balasubramanian and Hill, 2002).

2.2.4.2 Water seeding

Pre-germinated seeds are sown directly into water. Water seeding enables farmers to

proceed without waiting for the flood water recession necessary for wet seeding and to minimize

the risk of late season drought in the crop. Fields are drained gradually as the crop develops. This

practice substantially reduces weed infestations during early crop establishment (Yamauchi

1996).

2.2.4.3 Zero-tillage seeding

In South Vietnam after the harvest of the wet seeded rice crop in January or February,

rice straw is scattered over the fields, dried for a few days and burned. Fields are then irrigated to

an average depth of 5 cm before sowing pre germinated seeds onto the wet ash layer. In this way,

zero tillage shortens the turnover time when cultivating three rice crops per year. However, zero

tillage results in high weed infestations, particularly of perennial weeds such as Paspalum

distichum (Hach et al., 1997) and insect pest predators have been recorded significantly lower in

fields where stubble is burned (Loc et al., 1998).

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2.2.4.4 Dry seeding

This method is practiced when water is in short supply. Land preparation involves

ploughing or rotovation. Non-germinated seeds are broadcasted or drill seeded in dry or moist

soil. Broadcasted seeds are covered by harrowing; more seeds are required for broadcast than for

drill seeding and stand establishment is poor with broadcasting. Dry seeded rice culture is

practiced in Africa, Australia, Europe, and USA (Kwesi and De Datta, 1991).

2.3 Weeds

Weeds are plants growing in an improper place in competition with a crop. Thus, a plant

species cannot be classified as a weed under all conditions. The major weeds associated with rice

include grasses Dactyloctenium aegyptium (L.) Echinochloa crus-galli (L.), Echinochloa colona

(L.) and Leptochloa chinensis (L.), Cyperus rotendusand and broadleaf weeds Commelina

benghalensis (L.), Caesulia axillaris, Eclipta prostrate (L.) Euphorbia hirta (L.), Portulaca

oleracea (L.), Trianthema portulacastrum (L.) and Lindernia spp. (Singh et al., 2006).

2.3.1 Effects of weeds on rice

Weeds have different effects on rice. Weed infestations primarily constrain rice

production by reducing grain yield. Yield reductions caused by uncontrolled weeds throughout a

crop season have been estimated to be from 44 to 96 %, depending on the rice culture.

Worldwide some 9 % loss of rice yield can be attributed just to weeds (Oerke and Dehne, 2004).

There is considerable variation in yield loss to weeds among countries.

The cost of rice weed control including herbicides, cultural and mechanical practices and

hand weeding, is estimated to be about 5 % of world rice production and amount to US $ 3.5

billion annually. When the 9 % loss of rough rice paddy yield is added to this cost, the world’s

total estimated cost for rice weeds and their control amounts to 15 % of total annual production

of rice valued at US $ 10.5 billion (Kwesi De Datta, 1991). Similar findings were observed by

Norton et al. 2010 who reported that herbicide sales for rice crops globally grew at an average

rate of more than 2 percent year-1 from US $ 741 million in 1980 to US $ 1.34 billion in 2007

and global sale of herbicides for application in rice farming systems could reach US $ 3 billion

per year by 2025 (Zhang et al., 2004).

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Weeds indirectly limit production by serving as hosts for organisms that adversely affect

rice. Weeds provide food, shelter and reproduction sites for insects, nematodes, pathogens and

rodents. Some weeds that serve as alternate hosts to rice pests are Cynodon dactylon, Cyperus

iria, Echinochloa colona, Echinochloa crus-galli and Cyperus rotundus. This indicates the

importance of recognizing weeds as secondary hosts for pests and of removing weeds from the

margins of rice fields to prevent continued infection of the rice crop.

Weeds hamper rice harvesting and increase harvest costs through direct interference with

the harvesting operation and by causing lodging. Weed seeds contaminate rough rice, thus

reducing grain quality and market value. For example, the weed red rice has a pigmented layer

that shatters easily and readily contaminates rough rice. Removing all traces of the pigmented

layer requires intense milling resulting in decreased grain quality and increased cost. The

drudgery of weeding and labor shortages has made rice farming unattractive. In most tropical

countries, farmers spend more time on weeding by hand or with simple tools, than on any other

farming task.

Nutrient availability and favorable temperatures throughout the year, especially in the

tropics, allow luxuriant aquatic weed growth in rice fields and weeds compete for nutrients with

rice (Phoung et al., 2005). Heavy aquatic weed infestation causes excessive water loss through

evaporation and impedes water flow in irrigation canals. In some cases, aquatic weeds may be a

health hazard to persons living near impounded water. Weeds interfere with rice growth by

competing for one or more growth limiting resources such as light, nutrients and water.

Allelopathy (chemical production by living or decaying weed plant tissues) may also adversely

affect the growth of a neighboring rice plant. Rice and rice weeds have similar requirements for

growth and development. Competition occurs when one of the limiting resources falls short of

the combined requirements of both. The degree of rice-weed competition depends on rainfall,

rice variety, soil factors, weed density, duration of rice and weed growth. Cultural practices

greatly alter the competitive relationship between rice and weeds. Thus, different cultures

(irrigated, rain fed lowland, upland, and deepwater) will be subjected to different kinds and

degrees of weed competition. To understand this competition, it is essential to know the growth

requirements of rice and helpful to know the growth requirements of weeds.

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2.3.2 Weeds in direct seeded rice

Weeds are the main problem in direct seeded rice which may cause 100 % failure of the

crop. Aerobic soil, dry tillage and alternate wetting and drying conditions are favorable to the

germination and growth of weeds causing grain yield losses up to 90 % (Rao et al., 2007). Crop

loss due to weed competition varies with the duration of weed infestation of the crop. The crop is

likely to experience yield reduction, unless weeds are kept free during a part of its growing

period (Azmi et al., 2007). Johnson et al. (2004) noted that in direct seeded rice weeds can

emerge at the same time or before the rice plants, causing serious competition.

The labor requirement for weeding is a major impediment to the adoption of water saving

aerobic rice and increasing the productivity of aerobic rice based cropping systems (Singh et al.,

2006). After broadcast or drill seeding rice into dry soil field is irrigated just enough to provide

the soil moisture that allows the seeds to germinate. Thus, aerobic conditions remain ideal for the

germination of upland and aquatic weeds and weed problems are much worse in dry seeded

irrigated than in wet seeded rice (Kwesi and De Detta, 1991). Weeds are a major hurdle to broad

adoption of aerobic rice and greatest yield limiting constraint to aerobic rice, contributing about

50 % to yield losses (WARDA, 1996). Aerobic rice is subjected to more severe weed infestation

than transplanted lowland rice, because direct seeded aerobic rice germinates simultaneously

with weeds, in this way weeds dominates the crop due to the lack of water layer that suppress the

weed germination (Moody, 1983).

2.3.3 Weed control

Weeds have always reduced rice yields. As a result different weed control methods have

evolved. Farmers consider financial resources and availability of labor in deciding what weed

control method to use. Problems of input availability, availability of new technologies, specific

weed problems, farm size and availability of family labor are basic management factors in

making weed control decisions.

2.3.4 Planning effective control

Planning is important in making appropriate decisions on weed control. Unfortunately,

weed control usually is not planned. The decision to control is not made until the problem has

become serious, when control may be uneconomical, ineffective. Advance knowledge of weed

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problems can be obtained by surveying and recording the weed species in a rice field after rice

emergence. This record is useful in planning weed control and crop rotation programs.

2.4 Weed control methods

Weed control can be grouped into cultural, manual, mechanical, chemical, and biological

control methods. Each control method has advantages and disadvantages.

2.4.1 Cultural control methods

A basic principle of cultural control is to increase the competitive ability of rice and

enable it to suppress weed growth. Vigorous rice crop competes more effectively with weeds.

Cultural control methods includes; use of weed free and certified seed land preparation, cultivar

selection, time of seeding, planting method, crop rotation, plant population, fertilization and

water management (Rao et al., 2007).

2.4.2 Biological weed control methods

Several biological agents such as insects, mites, and fungi have been used successfully to

control rice weeds. The possibility of using tadpole shrimp (Triopus longicaudatus, T. granaris,

and T. cancriformis) for weed control in transplanted rice has been demonstrated in Japan. The

small crustaceans feed on weed seedlings and disturb their roots by mechanical agitation of the

soil. Labor for hand weeding in farmers’ fields was reduced 70-80 % in initial field trials with

tadpole shrimp (Matsunaka, 1975).

2.4.3 Problems of biological weed control methods

Tadpole shrimp (Triopus longicaudatus, T. granaris, and T. cancriformis) decreases

weed infestation but later on becomes a pest cause serious problems to rice crop (Matsunaka,

1975). Biological agents are selective in their control action and their activity may be restricted

to a single weed. Biological control programs may be applicable to an introduced perennial weed

growing in areas that are seldom disturbed, such as pastures, forests and water bodies. In a rice

cropping situation with a mixed weed flora, the selective control of a single weed will not solve

the weed problem and biological agents also work slowly.

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2.4.4 Manual weed control

Manual weed control includes removing and hand pulling. This method is the oldest and

in many cases, the farmer’s only way of controlling weeds in rice. Manual weeding is very

effective weed control method (Singh, 2005). Ekleme et al. (2009) conducted two field

experiments in Nigeria, results showed that lowest weed biomass (48 g m-2) was produced by

weeding twice with highest plant height (116 cm), tillers (203 m-2) and grain yield (3.62 t h-1) in

direct seeded rice. Singh et al. (2008) noted that hand weeding twice resulted in significantly

lower weed biomass (61.6 g) as compared to no weeding (329.5 g). Singh et al. (2007)

concluded that hand weeding six times in dry seeded rice resulted in lowest weed biomass (0 g

m-2) with highest panicle length (24.5 cm), panicles (160 m-2), grains panicle-1 (96), 1000 grain

weight (25.9 g), grain yield (5.58 t h-1) and straw yield (7.28 t h-1). Mann et al. (2007) conducted

an experiment and results revealed that in hand weeding with lowest weed biomass highest plant

height (92 cm), panicles (215 m-2), panicle length (27.3 cm), grains panicle-1 (120) and grain

yield (3.70 t h-1) were produced as compared to no weeding

Manual weeding is practiced in Cambodia at least twice and commonly three times

(Makara et al., 2001). In Vietnam, Chin et al. (2000a) found that hand weeding twice was the

most effective treatment in terms of both controlling weeds and crop safety in DSR. African

farmers normally rely on family labor for weeding in direct seeded rice, which usually starts at

15-30 DAS (Oteng and Sant’Anna, 1999). Chandra et al. (1998) concluded that hand weeding

resulted in lowest weed density, weed dry weight and highest grain yield over control. Bhaghat

et al. (1991) conducted a field experiment and results showed that hand weeding (15, 30 and 45

days after seedling emergence) produced highest paddy yield of 4.14 t ha-1.

2.4.5 Problems of manual weed control

Hand weeding is a very effective way to control weeds in DSR but it requires high labor

due to which cost of production also increases. Manual weeding can be done only when weeds

have adequate size to be pulled (Singh et al., 2005). Hand weeding in wet-seeded rice requires

more time (Moody, 1983). This labor demanding method requires 250–780 man h ha-1 (Stessens,

2002). Hand weeding is the most widely practiced intervention against weeds on small-scale rice

farms in Africa (Adesina et al., 1994) but shortage of labor, high labor cost, poor weather

15

conditions and the presence of perennial weeds that fragment on pulling are problems of hand

weeding

2.4.6 Chemical weed control methods

Herbicide use is one of the most labor-saving innovations that have been introduced in

rice farming. Hussain et al. (2008) used Nominee 100 SC to control weeds in direct seeded rice

resulting in grain yield (3.61 t ha-1) and giving 90 % weed control as compared to no weeding.

Effective weed management practices are an important requirement in DSR culture, with

herbicide application it is very easy to control weeds (Azmi et al., 2007). Islam et al. (2004)

compared hand weeding with different herbicides and found Pretilachlor as a most successful

weedicide with higher yield and cost benefit ratio. In America, Australia, Europe and East

Asia, over 90 % of DSR areas are treated with herbicides for weed control (Baltazar and De

Datta, 1992). Herbicide options for weed control in DSR differ according to method of crop

establishment because the performance of herbicides varies in relation to water regimes.

Extensive research has been conducted over the years by many researchers to find out the

optimum rate, time, type and method of herbicide application. Labor unavailability, high labor

costs and the urgent need to raise yields and maintain profit on a progressively limited land have

been major drivers for farmers to seek alternatives to manual weeding and herbicides are one

such alternative.

2.4.7 Problems of chemical weed control methods

Labor shortages have led to an increase in direct seeding and a rapid increase in the use

of herbicides. This reliance has resulted in an unwanted shift in weed species and concerns about

environmental pollution. Phenoxy and sulfonylurea compounds are extensively used herbicides

in Malaysia, Vietnam and Thailand to control broadleaf weeds and sedges in DSR. Weeds

resistant to these herbicides have developed and there is confirmation that weed species such as

S. zeylanica, Marsilea minuta, and F. miliacea have developed resistance to phenoxy herbicides

(Watanabe et al., 1997). Chemical weed control through the commonly used pre-emergence

herbicides (such as butachlor and thiobencarb) has been broadly investigated but their efficiency

depends on the water regime, soil tilth, composition of the weed and environmental conditions

(Baltazar and De Datta, 1992). Weedicide used for weed control in transplanted rice in Pakistan

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are not suitable for weeds in DSR and required weedicide for effective weed control in DSR are

not available.

2.4.8 Mechanical weed control

Mechanical weed control with the use of implements is a practical and economic method

for farmers. Mechanical weeding is almost generally practiced on row seeded rice since inter row

cultivation with either animal or tractor drawn implements reduces time in weed control and

minimizes crop damages. A weeder (with a straight line peg arrangement) showed outstanding

results on a range of soil types with unstable soil moisture levels and weed intensity and saving

57 % labor as compared with hand weeding (Subudhi, 2004). In Bangladesh a rake type weeder

had shown good results and it works in light and heavy soils with same efficacy (Islam et al.,

2004). Victor and Verma (2003) reported that Power operated rotary weeders have improved

weeding efficiency. In Thailand, a mechanized direct seeded rice management system has been

adopted, which includes weed control with a soil cultivator involving tillage between rows of

rice twice; 15 and 28 DAS (Kabaki et al., 2003). Mechanical weed control is similar to the weed

free control in terms of grain yield due to its bigger weed control efficiency (Morthy, 2003). In

Gambia effective weed management has been established with donkey drawn equipment using

twice (Remington and Posner, 2000). Beushening in which dry seeded rice is compressed by

‘‘planking’’ (drawing of a heavy flat wooden object over the crop) is also practiced to control

weeds. This process kills weed species with single main stems, whereas rice is able to retiller

from basal nodes. Sharma (1997) conducted a series of experiments on weed management in

rice, results showed that beushening is a very good technique to control weeds in rice, producing

paddy yield 3.5 t ha-1.

Comparisons of traditional and mechanically modernized weeding equipment suggest the

value of these technologies in resource limited farming communities. With labor shortage

mechanical weed control methods may be more efficient and suitable in DSR. Hence, efforts to

improve the effectiveness of existing weeding tools and implements are desirable, especially for

developing countries.