IJERD – International Journal of Environmental and Rural Development (2013) 4-1

Research article
erd

Economics of Weed Management in Maize in Pailin
Province Cambodia
VAN TOUCH*Post-Graduate Student, University of New England, Armidale, Australia.
Email: van.touch84@gmail.com

ROBERT J. MARTIN
Agricultural Systems Research Cambodia Co. Ltd., Battambang Cambodia

J. FIONA SCOTTNew South Wales Department of Primary Industries, NSW, Australia
Received 15 December 2012

Accepted 27 March 2013(*Corresponding Author)

Abstract In Pailin Province, Cambodia, small-holder farm households derive most of theirincome from upland cash crops such as cassava, maize, soybean, mungbean and sesame.
Since the end of the Khmer Rouge civil war in 1998, large areas of rainforest have beencleared opening the way for rapid expansion of cropping, especially maize. The crop
expansion has occurred on ferrosols and vertosols which had high initial fertility afterclearing. Continuous cropping with maize has resulted in a decline in soil fertility and anincrease in losses due to biotic factors, especially weeds which have contributed to adecline in maize yields. Due to the increased cost of agricultural labour, farmers have
rapidly taken up the use of herbicides for weed control in maize. A survey of 88
households in 6 villages was carried out to determine the effectiveness and economics ofweed control methods for maize, being used by farmers. The results indicate that farmers
are moving away from the traditional two cultivations for land preparation and two in-crop
hand weedings. This has been due to replacement of the second ploughing with presowing glyphosate, and the replacement of hand-weeding with selective in-crop herbicidesin response to the cost and scarcity of labour. Although the current herbicide-based system
for maize is working well, it is not likely to be sustainable without crop rotations and useof a wider range of herbicides. Maize crops in Pailin are being invaded by Sorghum weed
species, and these species are not controlled by the commonly used atrazine. Rotation ofcrops and herbicides will be necessary to prevent a build up of naturally resistant weeds
and development of genetic herbicide resistance in weed populations.
Keywords weed, management, maize, survey, rotation, economics

INTRODUCTION
Pailin town (12°50’47”   N,   102°36’48”   N)   is   located   in   North-Western Cambodia on the borderwith Thailand. The majority of farm households in Pailin Province depend on production of cash
crops such as cassava, maize, soybean, mungbean and sesame. However, the most common crop ismaize and production has expanded significantly since the end of the Khmer Rouge civil war in1998.
Farmers usually grow two crops of maize in the rainy season. Early Wet Season (EWS) maizeis planted in March-April and in the Main Wet Season (MWS), the crop is usually planted in JulyAugust (Chan et al., 2009).
Much of the land under production of maize has been cleared of rainforest or forest regrowthover the last 20 years. Most of the soils used for cropping are derived from basalt or limestoneparent material and have high natural fertility. The grain yield potential for maize in the region is 8
- 10 t/ha (Belfield and Brown, 2009). However, the average maize grain yield was estimated at 3.2t/ha in 2011, less than half of the potential (Brown and Johnstone, 2012).
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IJERD – International Journal of Environmental and Rural Development (2013) 4-1

There are a number of factors such as abiotic (light, water, temperature and nutrient) andbiotic (weeds, insects and pathogens) that contribute to decreased crop yields (Oerke, 2006). Weeds
are one of the major causes of poor yields on small-holder farms in Pailin. Due to the increased
cost of agricultural labour (USD 1/day in 2002 to USD 3/day in 2010) and shortage of labour,farmers have rapidly taken up the use of herbicides for weed control in maize.
OBJECTIVE
The aim of this study was to document weed management practices and to identify the social,economic and environmental constraints to the adoption of better weed management practices inPailin Province, Cambodia.
METHODOLOGY
Data were collected from maize growers in six villages in Boryakha Commune in Pailin. A total of
88 households were selected randomly for the study. Sample size was determined using the Yamane
formula (Yamane 1967) to give a 10% margin of error. Households were selected from the Villagesof Borhuy (22), Boryakha (15), Rong Chak (11), Bortainsou (16), O Chra Lech (14), and O Sngout(10).
Qualitative data were obtained from the respondents using a pre-tested, structured interview
conducted by enumerators who were familiar with the existing social settings. The interview
schedule included both open-ended and closed-ended questions.
Descriptive statistical tools were used to analyze the quantitative data. The important statisticalmeasures that were used to summarize and categorize the data were means, percentages,
frequencies and standard deviations using Excel and the IRRISTAT statistical package was used for
regression analysis (Anon., 2011).
Farmers were asked about the yield obtained, the price received for the crop and the variable
costs of land preparation, seed, planting, weed control, harvesting, threshing and transportation.
These data were used to calculate the gross margin (income minus variable costs).
RESULTS AND DISCUSSION
The average household size in the study area is 5.25 people, of which 3.13 are working age adults
and the average area of crop fields per household is 4.04 ha (Brown and Johnstone, 2012). Thismeans that all of the activities such as planting, weeding and harvesting cannot be completed
manually by family members. As a result Pailin farmers have begun to mechanize land preparation,and planting and have replaced in-crop hand weeding with selective herbicides.
The average yield was 4.07 t/ha and the average price was USD 172/t giving a total income ofUSD 700/ha. The average total cost of inputs for maize was USD 275 per hectare, and the highest
and lowest costs were USD 491 and USD 143 respectively. The average gross margin was USD
425 per hectare, and some farmers had gross margins up to USD 1,152 while the others madelosses of as much as USD 62. On average, farmers obtained a return of USD 1.54 per USD 1 spent
which was considered a good return on investment. Break-even yield is the yield at which the grossmargin equals zero and is calculated by dividing variable costs by the expected price (Table 1).
Table 1 Economic analysis of maize production in Pailin (per hectare)
Costs
Yield
IncomeVariable costs
Gross margin
Gross margin/USD cost
Break-even yield

Average

Maximum

MinimumMedian4.07
USD 700
USD 275
USD 425
USD 1.541.60

8.27
USD 1,422
USD 491
USD 931
USD 2.35
2.86

1.05
USD 180
USD 143
USD 37
USD (0.43)
0.83

3.97
USD 682
USD 271
USD 411
USD 1.15
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IJERD – International Journal of Environmental and Rural Development (2013) 4-1

The breakdown of variable costs is given in Table 2. The traditional practice for land
preparation is for two ploughings and often a harrowing. Pailin maize farmers have reduced theamount of cultivation where only 59% are ploughing the field a second time. This reduction isconsistent with the number of farmers using glyphosate which is 33%. It is assumed from thesedata that farmers are beginning to replace the final cultivation with a glyphosate application. This isa positive trend because reduced cultivation reduces the potential for soil degradation, increases theconservation of soil moisture for the crop and can improve the timeliness of sowing.
Table 2 also shows that there has been a strong trend away from hand planting with 44% of
farmers hand planting compared to 52% machine planting. There is also a minority of farmers
using hand-weeding for weed control: 34% for one hand-weeding and only 16% hand-weeding asecond time.
The reduction in hand-weeding is associated with a high adoption of selective in-crop
herbicides with 80% of maize farmers using atrazine and 78% using 2,4-D; with more than 97% of
the two herbicides being mixed together and spayed at one time. The study also showed that a few
farmers had used Atrazine alone to control weeds without the combination of 2,4 D. There are also
68% of farmers using paraquat as a late post-emergence directed in-crop spray.
Table 2 Breakdown of variable costs for maize production in Pailin
Input
1st ploughing
2nd ploughing
SeedHand planting
Machine planting
1st hand weeding
2nd hand weeding
Atrazine
2,4-D
Paraquat
Glyphosate
1st spraying
2nd spraying
3rd spraying
HarvestThreshingTransport
Total variable costs

Farms (%)
9859
100
4452
34138078
68333985
76
100
280
100

Average input cost
USD 43.29
USD 20.86
USD 59.96
USD 15.39
USD 14.97
USD 6.58
USD 1.62
USD 3.69
USD 2.46
USD 9.18
USD 3.71
USD 2.37
USD 7.23
USD 6.58
USD 58.49
USD 0.59USD 18.10
USD 275.37

The overall average input costs do not give an accurate idea of input costs for the different
cultivation and weeding strategies. Therefore the data were re-analyzed according to the followingclassifications:Replacement of the second cultivation with glyphosate with treatments being:
1. No second cultivation and no glyphosate;
2. Second cultivation and no glyphosate;
3. Second cultivation plus glyphosate;
4. Glyphosate only.
Replacement of hand-weeding with in-crop herbicides with treatments being:
1. Hand-weeding only;
2. Hand-weeding plus in-crop herbicide;
3. In-crop herbicide only.
This analysis confirmed the trend for pre-sowing glyphosate being used to replace the secondcultivation (Table 3). The input cost for glyphosate (USD 19.95/ha) was significantly lower thanfor cultivation (USD 34.69/ha). The cost of a second cultivation plus glyphosate (USD 47.22/ha)
was significantly greater than cultivation or glyphosate alone. There were no significant effects oncrop yield or gross margin for the substitution of the second cultivation with glyphosate. However,Ⓒ ISERD217

IJERD – International Journal of Environmental and Rural Development (2013) 4-1

reduction in cultivation is likely to reduce soil fertility decline and soil erosion and therefore
deliver economic benefits in the future (Kelley, 1983).
Table 3 Effect of substitution of the second cultivation with pre-sowing glyphosate on yield,
input costs and gross margin per hectare
2nd ploughing

Glyphosate

No. of farms

NoNo
Yes
Yes

2138
1415

No
Yes
Yes
NoSE
5%LSD
SignificanceYield (kg/ha)

Input cost

3,986
4,181
4,309
4,032
317
892
NS

0.00
34.69
47.22
19.95
1.31
3.690.01

Gross margin
400.75453.39355.72451.6559.80
168.17
NSA total of 9 households (10%) practiced hand weeding only (Table 4) and the average cost ofweed control for hand weeding only was USD 35.19/ha. Twenty two households used both hand
weeding and herbicide at a cost of USD 53.71/ha. The majority of households (57) used herbicide
only for weed control at a cost of USD 36.53/ha. Although there was a higher yield (NS) for handweeding plus herbicide, the cost was significantly greater than for hand-weeding or herbicide alone.
Although not significant, the gross margin for herbicide alone was the highest.
Table 4 Effect of replacing hand-weeding with in-crop herbicides on yield, input costs andgross margin per hectare
Hand-weeding
Yes
Yes
NoSE
5%LSD
Significance

Herbicide
No
Yes
Yes

No. of farms
92257

Yield (kg/ha)
3,596
4,343
4,132273767
NSInput cost
35.19
53.71
36.53
5.10
14.33
0.01

Gross margin369.73412.22438.6552.09
146.46NS

Table 5 Regression of gross margin on the components of variable costs
TermConstantYield (kg/ha)
1st ploughing
2nd ploughing
Seed
Hand planting
Machine planting
1st hand-weeding
2nd hand-weeding
Atrazine
2,4-D
Paraquat
Glyphosate
1st spraying
2nd spraying
3rd spraying
HarvestThreshingTransport
Price per tone

Coef.
-729.36
0.1625-1.1686-1.1747-0.5087-0.3599-0.9734-1.2092-0.06812.1125-8.6845-0.6807-0.1541-4.4487
0.6463-3.6185-0.4189-0.3736-0.55074.0713

SDEV
61.7903
0.00600.56930.47690.60000.44430.42190.59101.91545.6101
6.47350.79911.67903.19092.4113
1.40810.39682.2482
0.52270.1633F-value
139.3280
723.3630
4.21406.06800.71900.65605.32204.18600.00100.14201.80000.72600.00801.94400.07206.60301.11400.02801.1100621.7920

P
0.00000.00000.04200.0160NSNS
0.02300.0420
NSNS
NS
NS
NS
NS
NS
0.0120NSNS
NS
0.0000Multiple regression analysis (Anon., 2011) was used to determine if individual variable costand income components had an effect on the gross margin (Table 5). The cost of ploughing,machine planting, hand-weeding once and the third spraying all had a significant negative effect onⒸ ISERD218

IJERD – International Journal of Environmental and Rural Development (2013) 4-1gross margin. Therefore the farmers should concentrate on reducing these costs to improve
profitability.
Grain yields ranged from 900 to 8,333 kg/ha with an average of 4,130 kg/ha. The regressionof gross margin on maize yield shows that, on average, for every extra tonne of yield the grossmargin increased by USD 130. The price received for maize varied between USD 70 and USD 250per tonne with an average of USD 172 per tonne.
93% of farmers used herbicides and 68% of these were satisfied with this method because
their fields were mostly large and they had insufficient labour for hand-weeding. 87% of herbicide
users reported good herbicide efficacy and quick action, 11% reported ineffective control, and 3%
were concerned that herbicide application could have negative effects on soil and human health.
There were three main reasons that led farmers to apply herbicide: less costly than hand-weeding;convenience and fast action; and labour shortage.
CONCLUSION
This study documented trends in practices for weed management in Pailin Province Cambodia. The
main drivers for change appear to have been the cost and availability of hand labour. This has led
to mechanization of land preparation, and sowing and to the replacement of in-crop hand weedingwith selective herbicides.
Although the current herbicide-based system for maize is working well, it is not likely to besustainable without crop rotations and use of a wider range of herbicides. Maize crops in Pailin arebeing invaded by Sorghum bicolor (Shattercane) and S. halepense (Johnson grass) that are notcontrolled by atrazine. Rotation of crops and herbicides will be necessary to prevent a build up ofnaturally resistant weeds and development of genetic herbicide resistance.
ACKNOWLEDGEMENTS
We would like to acknowledge the Australian Centre for International Agricultural Research(ACIAR) for funding this research.
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