PertanikaJ. Trop. Agric. Sci. 27(2): 1 1 3 - 1 2 0 (2004) ISSN: 1511-3701© Universiti Putra Malaysia Press

A Study of Weed Populations and Their Buried Seeds in the Soil of MARDIResearch Station and at Farmers' Rice Fields in Sungai Burung,

Tanjung Karang, Selangor, Malaysia

ISMAIL B. S. 8c K. PHAIK-HONGSchool of Environmental and Natural Resource Sciences,

Universiti Kebangsaan Malaysia43600 UKM, Bangi, Selangor Darul Ehsan, Malaysia

Keywords: Weed flora composition, transplanted rice field, direct seeding, seedbank

ABSTRAK

Kajian populasi rumpai dan biji yang tertanam sebelum dan selepas penuaian telah dilakukan di kawasansawah di Stesyen Penyelidikan MARDI dan Sungai Burung, Selangor. Hasil menunjukkan bahawa rumpaiberdaun lebar sangat dominan di kawasan sawah di Stesyen MARDI dan Sungai Burung. Dua spesies iaituCyperus difformis (rusiga) dan Najas graminae (daun lebar), masing-masing merupakan spesies dominan dikedua-dua kawasan tersebut Populasi biji rumpai tidak berbeza di antara kedua-dua kawasan tersebut. Bagai-manapun, biji rumpai yang dikira sebelum dan selepas penuaian menunjukkan perbezaan bilangannya. Padaumumnya bilangan biji yang tertinggi di kedua-dua kawasan sawah tersebut dikesan pada kedalaman 0-5 cm.

ABSTRACT

A study of weed populations and their buried seeds before and after harvesting was carried out at the MARDIResearch Station and at Farmers' Rice Fields, Sungai Burung in Tanjung Karang, Selangor. The results showedthat the broadleaf weeds were the most dominant in the MARDI and Sungai Burung rice fields. Two species,namely Cyperus difformis (sedge) and Najas graminae (broadleaf) were the most dominant species in theMARDI and Sungai Burung rice fields respectively. The weed seed populations were similar in both rice fields.However, the weed seed counts before and after harvesting were different. In general, it was also found that thehighest number of weed seeds in the soil was detected in the 0-5 cm layer of soil in both rice fields.

INTRODUCTION

Weed infestation is one of the most problematicand troublesome scenarios in rice cultivation.Factors such as cultivation practice, landpreparation, soil moisture content andmanagement strategies greatly affect the presenceand abundance of weeds in rice fields (De Datta1981). Previous studies have shown that weedsfound in direct seeded rice fields were morecomplicated than those in transplanted rice fields(Teerawatsakul 1976; Tengku Zunaidah 1996).As reported, weed composition and dominancewere affected by water management and soilpreparation. Rice field soils, which are flattenedand submerged in water in the early stage ofland preparation coupled with proper tillage,could reduce the growth of weeds (Khalid 1988;Yamada 1965). Noda (1977) reported that weedsin transplanted and direct seeded rice fields

caused rice yield losses of 16 and 62%,respectively.

Weed problems begin with weed seeds inthe soil and they continuously create problemseven though attempts are made to prevent themfrom going to seed in the field (Wilson et al1985). Thus, knowledge of the total numberand type of buried seeds is very useful inpredicting which species are likely to emerge ina particular field (Lawson 1988). Reports onweeds from rice fields in Tanjung Karang arevery limited. Recently, it was reported thatLimnophila erecta and Bacopa rotundifolia were thenewly detected dominant weeds in Sekinchan(Azmi and Baki 2003). Experiments were thereforeconducted to determine the weed floracomposition and seed population in wet-seededrice fields in Tanjung Karang, Selangor.

ISMAIL B.S. & K. PHAIK-HONG

MATERIALS AND METHODS

The Study Area

The study was conducted at the Research Stationof MARDI and farmers' rice fields in SungaiBurung, Tanjung Karang, Selangor. The MARDIand Sungai Burung areas have 9.6 and 2,000 haof rice fields respectively. Farmers in MARDIpractise the wet direct seeding method in themonsoon season (jun-Oct 2000) and thetransplanting method in November-March(2000/01). Almost 98% of the rice fields inSungai Burung are wet-direct seeded and themain sources of water supply are irrigation canalsand rain.

Weed Population DeterminationTwo plots from each study area were selectedrandomly and used for the weed populationassessment study. The paddy plants wereapproximately 2 to 2 V2 months old in bothsites. Weeds from each of thirty 1-m2 quadrats(Kim and Moody 1983) in each plot were removedand counted by species. Summed dominanceratio (SDR) of each species was determinedfrom the sum of the relative density, relativeabundance and relative frequency.

Seed Bank Sampling

Soil samples were taken from the same locationsas those used for weed population determination.Soil samples 7 cm in diameter were taken up toa depth of 15 cm from 30 quadrats in each studysite. The soil depth of 15 cm was studied asreports have shown that the viability of the seeddecreased at the depth of 10 cm and the buriedseeds were skewed within the first 10 cm soildepth besides being well-correlated to theseedling emergence in fields (Baki et al. 1997;Graham and Hutchings 1988; Wilson et al 1985;Zoner et al 1984). The soil cores were dividedinto three different sections according to depth:0-5 cm, 5-10 cm and 10-15 cm. Soil samples ofthe same depth for each particular site werepooled, mixed thoroughly and air-dried. Thesoil sampling before harvesting was conductedwhen the paddy plants were 2 to 2 V2 monthsold whilst soil samples after harvesting weretaken immediately after the crop was harvested.All sampling was done from the wet-direct seededrice fields at both sites.

A modification of the seed separationmethods described by Wilson et al (1985),

Sastroutomo and Yusron (1987) and Ball andMiller (1989) were used. For each soil, a 400 gsoil sample was soaked in water and passedthrough a sieve with a screen size of 250 \m\ tocollect weed seeds. Water was run through thescreen to enhance sample movement. Thecontents collected in the screen were removedand air-dried. Seeds from the entire sampleswere sorted using a dissecting microscope andcounted according to species. The total numberof buried seeds found in the soil at differentdepths was expressed in numbers per m2.

RESULTS

Weed Composition

P± total of 17 weed species belonging to 13families were found in these arable sites (Table1). Among the families, Poaceae was the familywith the highest number of species. Generally,broadleaf weeds were the most dominant (9species) compared to grasses (4) and sedges (3).A species of aquatic ferns {Marsilea crenata Presl)from the family Marsileaceae was identified too.The number of weed species in the MARDI ricefields was slightly higher (14 species) than thatin the Sungai Burung (13 species) area.

There were four species with SDR values ofmore than 5% in the MARDI rice fields. Themost dominant weed was Cyperus difformis L. witha SDR value of 12.14%, followed by Mimulusorbicularis (Bl.), Lemna minor L. Griff andLimnocharis flava Buchenau in the respectiveorder of 10.12, 7.78 and 5.39%. However in theSungai Burung rice fields, the hierarchical orderof the dominant weed species was Najas graminea(non Del.) Ridl, L. minor, Sagittaria guayanensisKunth, Hydrilla verticullata (L.f) Royle andMonochoria vaginalis (Burm.f.) Presl with SDRvalues of 12.77, 8.92, 7.14, 5.42 and 5.19%respectively.

Based on the SDR value, the broadleavedweeds dominated the weed community in theMARDI and Sungai Burung rice fields accountingfor ca. 32.48% and 39.60% respectively (Fig, i).

Weed Seed Population in the SoilTables 2 and 3 illustrate the number of speciescollected from the study sites. Twenty-four speciesof weed seeds were recorded. The total weedseed populations in both rice fields were quitesimilar for both harvest times (369,720 and526,042 seeds/m2 in MARDI; 390,721 and535,316 seeds/m2 in Sungai Burung before and

114 PERTANIKAJ. TROP. AGRIC. SCI. VOL. 27 NO. 2, 2004

A STUDY OF WEED POPULATIONS AND THEIR BURIED SEEDS

Species

TABLE 1Summed dominance ratio values of weeds in transplanted rice fields of the Research

Center MARDI and farmers' fields in Sungai Burung, Tanjung Karang, Selangor

SDR (%)

MARDI Sungai Burung

AlismataceaeSagittaria guayanensis

Li m n oc h ari tace aeLimnocharis flava

CyperaceaeCyperus difformisCyperus iria

HydrocharitaceaeHydrilla verticillata

LemnaceaeLemna minor

LentibulariaceaeUtricularia aurea

LythraceaeRotala indica

MarsileaceaeMarsilea crenata

NajadaceaeNajas graminea

OnagraceaeLudxvigia adscendens

PoaceaeDigitaria adscendensEchinochloa cofanaEchinochloa crus-galliLeptochloa chinensis

PontederiaceaeMonochoria vaginalis

ScrophulariaceaeMimulus orbicularis

5.39

12.142.96

1.57

7.78

0.88

1.65

1.37

3.52

0.70

2.213.76

2.44

10.12

7.14

5.42

8.92

1.03

3.54

1.50

12.77

1.01

0.562.653.481.79

5.19

5.97

MARDI

1.37

16.67 32.48

8.48

5.42

Fig. 1: SDR values of broadleaved weeds ( £ ] ) , grasses( [ ] )t sedges ( £aquatic ferns fPIl ) in MARDI and Sungai Burung rice fields

) and

PERTANIKA J. TROP. AGRIC. SCI. VOL. 27 NO. 2, 2004 115

ISMAIL B.S. 8c K. PHAIK-HONG

TABLE 2The distribution of weed seeds at the depth of 0-15 cm soil profile

of arable rice fields in MARDI, Tanjung Karang, Selangor

Species

Before harvesting

Cyperus iriaEchinochloa colonaLimnocharis flavaScirpus juncoidesLeguminosaeEleocharis acicularisMonochoria vaginalisUtricularia aureaNajas gramineaOryza sativa*Cyperus diffarmisEchinochloa crus-galliSagittaria guayanensisCleome viscosaI^emna minorEchinochloa stagninaI^ptochba chinensisUnidentifiedFimbristylis miliaceaTotal

After harvesting

Cyperus iriaLimnocharis flavaEchinochloa colonaUtricularia aureaOryza sativa*l^eguminosaeCleome viscosaScirpus juncoidesMonochoria vaginalisCyperus difformisLudwigia octovalvisNajas gramineaEleocharis acicularisLemna minorEchinochloa crus-galliEchinochloa stagninaIjeptochloa chinensisFimbristylis miliaceaUnidentifiedDactyloctenium aegyptium

Total

0-5

33,35118,33217,11712,70011,37510,1608,8355,9635,3017,1787,8414,4172,7612,7612,430552994

1,2150

153,283

53,00831,59720,68312,47319,64416,11010,39311,5377,7959,3545,7176,4446,2366,0284,4691,1431,4552,183935832

228,036

5-10

25,95820,58011,45912,1619,7056,6657,6009,939*5,8473,8592,1054,5606,3143,5084,2092,3391,403

01,169

139,380

35,31332,03918,70918,0077,01613,21311,1089,8227,0163,5088,1854,6773,8593,6254,6774,2093,8591,403818584

191,647

Soil depth (cm)

10-15seeds/m2

16,95514,26510,0569,1219,1213,1572,8061,9881,754468

1,0521,637818

3,274000

5850

77,057

16,83821,04710,75811,9276,1971,0066,1975,9635,1454,4432,5723,6252,3391,8712,3391,169819

2,10400

106,359

0-15

76,26453,17738,63233,98130,20119,98219,24117,89012,90211,50510,99810,6149,8939,5436,6392,8912,3971,8001,169

369,720

105,15984,68350,15042,40732,85730,32927,69827,32219,95617,30516,47414,74612,43411,52411,4856,5216,1335,6901,7531,416

526,042

%

20.6314.3810.459.198.175.415.204.843.493.112.972.872.682.581.800.780.650.480.32

100.00

20.0016.109.538.066.255.775.275.193.793.293.132.802,362.192.181.241.171.080.330.27

100.00

Paddy

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A STUDY OF WEED POPULATIONS AND THEIR BURIED SEEDS

TABLE 3The distribution of weed seeds at the depth of 0-15 cm soil profile of farmers'

arable rice fields in Sungai Burung, Tanjung Karang, Selangor

Species

Before harvesting

Najas gramineaSagittaria guayanensisScirpus juncoidesMonochoria vaginalisEchinochloa colonaUtricularia aureaCleome viscosaEleocharis acicularisOryza sativa*Limnocharis flavaCyperus iriaCyperus difformisEchinochloa crus-galliLemna minorUnidentifiedI^eptochloa chinensisLudurigia octovalvisTotal

After harvesting

Najas gramineaScirpus juncoidesEchinochloa colonaSagittaria guayanensisUtricularia aureaMonochoria vaginalisOryza sativa*Eleocharis acicularisEchinochloa crus-galliCleome viscosaLimnocharis flavaCyperus difformisCyperus iriaLudwgia octovalvisl^guminosaeCyperus compressusLeptochloa chinensisUnidentifiedIjmna minorTotal

0-5

35,69327,33226,36816,50710,29012,97010,6117,39611,8986,0027,0742,3584,7165,7881,1792,3591,822

190,363

76,47248,05827,24512,97929,93411,22515,08410,2909,8227,1332,4565,1452,3391,6371,1692,3391,052819350

265,548

5-10

23,83916,76811,71815,65718,4356,3647,3748,9904,4457,7783,2326,4652,1211,3132,9291,212707

134,347

47,55230,01220,13827,41412,73215,9808,0558,1854,8072,7284,4172,3393,2483,248

' 3,3781,5601,5601,819

0199,172

Soil depth (cm)

10-15seeds/nv1

10,5137,1048,80812,7867,3885,1152,1781,9881,7052,1781,515947852378

2,2720

28466,011

14,0968,29911,1419,4366,2531,8193,6382,5012,3871,2503,4102,0461,592455796

0568341568

70,596

0-15

70,04551,20446,89444,95031,11324,44920,16318,37418,04815,95811,8219,7707,6897,4796,3803,5712,813

390,721

138,12086,36958,52449,82948,91929,02426,77720,97617,01611,11110,2839,5307,1795,3405,3433,8993,1802,979918

535,316

%

17.9313.1112.0011.507.966.265.164.704.624.083.032.501.971.911.640.910.72

100.00

25.8016.1310.939.319.145.425.003.923.182.081.921.781.341.001.000.730.590.560.17

100.00

paddy

PERTANIKAJ. TROP. AGRIC. SCI. VOL. 27 NO. 2, 2004 117

ISMAIL B.S. 8c K. PHAIK-HONG

TABLE 4Estimation of weed seeds found in the arable soil at the Research Station MARDI

and in farmers' fields Sungai Burung, Tanjung Karang, Selangor1

Soil depth (cm) Estimated mean number of seed (seeds/m2)

Before harvesting

153,283 a139,380 a77,057 b369,720

190,363 a134,347 b66,011 c390,721

After harvesting

228,036 a191,647 a106,359 b526,042

265,548 a199,172 b70,596 c535,316

MARDI0-55-1010-15Total*

Sungai Burung0-55-1010-15Total*

a Means in a column followed by the same letters are not significantly different (P>0.05) according to theTukey test.

* The total seed count between before and after harvesting is significantly different at the 5% level asdetermined by Tukey test.

after harvesting, respectively). Nevertheless, theestimated number of weed seeds after harvestingwas higher than the number before harvesting(Table 4). Nineteen and twenty species of weedseeds were recorded in the MARDI rice fieldsbefore and after harvesting, respectively.Meanwhile, the corresponding number was 18and 17 species in the Sungai Burung rice fields.The seeds of Cyperus iria L. were the mostabundant in the MARDI rice fields while N.gramineah&d the highest percentage of total seedsfound in the Sungai Burung rice fields irrespec-tive of the harvest time. Most of the weed seedswere found in the top 5 cm of the soil at bothsites. In general there was a significant differencein the seed count at the different depths of theSungai Burung soil. The total number of weedseeds declined with increasing depth, i.e. theywere lower at 10-15 cm than at 0-5 cm.

DISCUSSIONAccording to the findings of Saharan (1977),the most common broadleaved weeds found inrice fields were M. vaginalis, L. flava, S. guayanensisand Jussiaea repens. All these species except /repens were found in this study. The abundanceof broadleaf weeds in both study sites indicatesthat flooding has a major suppressive effect onthe stand establishment and growth of grassesand sedges. Anon (1982) and Moody (1977)

reported that almost all weeds cannot survive inwater at the depth of more than 10 cm, exceptcertain broadleaved weeds.

Seventeen out of the 55 weed speciesrecorded by Itoh (1991) were identified in theMARDI and Sungai Burung rice fields. Only twospecies were in the group of common weeds, viz.L. minor and Scirpus juncoides meanwhile twoother species (H. verticullata and Rotala indica)were rare species. Drost and Moody (1982)reported that moisture or saturated soilconditions after planting was the major factoraffecting the composition of the weed flora andthe dominance patterns of the major weedgroups in particular populations. Water suppliedto rice fields after seeding hinders theestablishment of sedges and grasses. The SDRvalues reflect this, as the value for broadleaves ismore than double those obtained for sedgesand grasses. Thus, flooding favoured the growthof broadleaved weeds over sedges and grasses(Ho and Itoh 1991).

The total numbers of buried seeds (includingviable and non-viable seeds) in the two siteswere similar. This was due to the geographicalfactor. Both study sites were close to each other(5 km apart) and irrigated by canals from thesame point. Kelly and Bruns (1975) have proventhat water played a significant role in the processof weed dissemination. The same source of

118 PERTANIKAJ. TROP. AGRIC. SCI. VOL. 27 NO. 2,2004

A STUDY OF WEED POPULATIONS AND THEIR BURIED SEEDS

irrigation might contribute to the similarity ofweed seed counts at both sites.

On the other hand, seed counts before andafter harvesting were significantly different inboth areas. In most cases, the life cycle of weedsin rice fields is shorter compared to that of therice plant. Within 3 months, weed seeds willripen and fall, thus contributing to the seedreservoir in the soil. For instance, E. crus-galli hasa growth duration of 90 days, which is shorterthan the maturation period of the paddy plant(via. 120 days) (Azmi 1990). Thus, the weedseed population in the soil is higher after theharvest period. It is also reasonable to suggestthat the species found possess characteristicallyefficient and strong vegetative growth coupledwith the ability to produce a vast number ofseeds.

Weed seeds of both rice fields were skewedmostly to the first 0-5 cm soil depth accountingfor ca. 41.5 to 43.3% and 48.7 to 49.6% of thetotal seed counts in the MARDI and SungaiBurung rice fields, respectively. The large numberof seeds may appear to be those seeds buriedduring previous years and the continuous seedshedding by the existing weeds onto the soilsurface. Baki et al. (1997) have also proven thatthe total seed counts are high in the first 0-5 cmsoil depth in arable peat of Selangor, Malaysia.

The depth from which soil samples are takenis an important factor to estimate the seedbankin the soil (Zhang et al 1998). Studies haveshown that burial depth significantly affects seedgermination and seedling emergence in a varietyof plant species under both greenhouse andfield conditions (Fenner 1985; Maun andLapierre 1986). In our study, soil samples weretaken up to a depth of 15 cm to determine thedensity of the soil seedbank. This is becausetaking soil samples to ploughing depth mayincrease the chances of sampling the seeds ofweed species in an area and thus enhance thedegree of accuracy in the estimation of theexisting soil seedbank.

Seedbanks can make eradication of weedsvery difficult. It is possible to locate and destroygrowing plants, but dormant viable seeds mayremain undetected in the soil for many yearsand later on give rise to a new population ofplants. Therefore, control of weed seed populationin the soil is necessary for better weed mana-gement (Ismail and Kalithasan 1994) and maybe more practicable if the seeds in the active soil

seedbank are used (Zhang et al 1998). Furtherstudies on the viability of the weed seeds arerequired to achieve this goal.

ACKNOWLEDGEMENTSThis work was supported by research grant IRPA09-02-02-0073-EA200 from the Ministry ofScience, Technology and Environment ofMalaysia.

REFERENCESANON. 1982. Annual Report. Rice Research

Branch. MARDI: 131-151.

AZMI, M. 1990. Critical period for weed controlin direct seeded rice. Proc. 3rd Tropical WeedScience Conference, p. 75-91. Malaysian PlantProtection Society, K.L.

AZMI, M. and B. B. BAKI. 2003. Weed speciesdiversity and management practices in theSekinchan Farm Block, Selangor South WestProject - A highly productive rice area inMalaysia. Proc. 19th Asian-Pacific Weed ScienceSociety Conference, p. 174-184. Weed ScienceSociety of the Philippines, Manila.

BAKI, B.B., W.K. YONG and N.Y.F. WONG. 1997.

Quantitative assessments and spatial patternamalyses of weed seed banks of arable peatin Selangor, Malaysia. The Korean J. of WeedSci. 17(3): 269-280.

BALL, D.A. and S.D. MILLER. 1989. A comparisonof techniques for estimation of arable soilseed banks and their relationship to weedflora. Weed Res. 29: 365-373.

DE DATTA, S.K. 1981. Principles and Practices ofRice Production. New York: Wiley 8c Sons.

DROST, D.C. and K. MOODY. 1982. Effect ofbutachlor on Echinochloa glabescens in wet-seeded rice (Oryza sativa). Philippines J. WeedSci. 9: 57-64.

FENNER, M. 1985. Seed Ecology. New York: Chapman8c Hall.

GRAHAM, D.J. and MJ. HUTCHINGS. 1988.

Estimation of the seed bank of a chalkgrassland ley established on former arableland. / Applied Ecol 25: 241-252.

Ho, N.K. and K. ITOH. 1991. Changes of weedflora and their distribution, in the Mudaarea. In 8th MADA/TARC Quarterly Meeting.Kedah: Alor Setar.

PERTANIKAJ. TROP. AGRIC. SCI. VOL. 27 NO. 2, 2004 119

ISMAIL B.S. & K PHAIK-HONG

ITOH, 1L 1991. Life Cycles of Rice Fields Weeds andTheir Management in Malaysia. Japan: TropicalAgricultural Research Center.

ISMAIL, B.S. and K. KAUTHASAN. 1994. Effects ofglufosinate-ammonium and terbuthylazineon germination and growth of two weedspecies. Plant Protection Q 9: 15-19.

KHALID, S.C. 1988. Masalah rumpai danperlaksanaan program pengurusan dalamkawasan KADA. Pros. Seminar & BengkelPengurusan Rumpai Sawah Padi Kebangsaan, 7-9 Jun, Pulau Pinang, Malaysia.

KELLY, A.P. and V.F. BRUNS. 1975. Disseminationof weed seeds by irrigation water. Weed Sri.23: 486.

KIM, S.C. and K. MOODY. 1983. Effect of a mixtureof two rice cultivars on the competitive abilityof rice against weeds and rice grain yields.Philipp. I Weed Sri. 7: 17-25.

LAWSON> H.M. 1988. The use of weed seedbankin the selection of herbicide recommen-dations. Weed Res. 28: 486.

MAUN, M.A. andj. LAPIERRE. 1986. Effects of burialby sand on germination and seedling emer-gence of four dune species. American J. ofBotany 73: 450-455.

MOODY, K. 1977. Weed control in rice. In 5th

BIOTROP Weed Srience, p . 374-424. K.L.:Rubber Research Institute.

NODA, K, 1977. Integrated weed control in rice.In Integrated Control of Weeds, ed. J.D. Fryer,and S. Matsunaka, p. 17-46. Tokyo: Univ. ofTokyo Press.

SAHARAN, H.A. 1977. Rice weed control inMalaysia. MARDI Report No. 66, Serdang.

SASTROUTOMO, S.S. and A. YUSRON. 1987. Buriedweed seed population in arable soils. 11th theAsian-Pac. Weed Sri. Soc. Conf, pp. 46-60.Nov. 29-Dec. 5, Taipei, Rep. of China.

TEERAWATSAKUL, M. 1976. Weeds in paddy fieldand their control in Thailand. Weeds andWeed Control in Asia. Food and FertilizerTechnology Centre, China. Aug. 1981.

TENGKU ZUNAIDAH, TJ. 1996. Kajian populasirumpai dan biji rumpai dan tanah diTanjung Karang, Selangor. Tesis SarjanaMuda Sains. Universiti Kebangsaan Malaysia,Bangi.

WILSON, R.G., E.D. KERR and L.A. Nelson. 1985.Potential for using weed seed content in thesoil to predict future weed problems. WeedSet. 33: 171-175.

YAMADA, N. 1965. Problems of irrigation anddrainage practices in rice culture. Int. RiceCom. Newsl. 14(3): 13-31.

ZHANG, J., A.S. HAMILL, I.O. GARDINER and S.E,

WEAVER. 1998. Dependence of weed flora onthe active soil seedbank. Weed Res. 38: 143-152.

ZORNER, P.S., R.L. ZIMDAHL and E.E. SCHWEIZER.

1984. Effect of depth and duration of seedburial on kochia (Kochia scoparia). Weed Sci.32: 602-607.

(Received: 10 September 2003)(Accepted: 20 April 2005)

120 PERTANIKAJ. TROP. AGRIC. SCI. VOL. 27 NO. 2, 2004