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EFFECT OF INCORPORATED COMMON SUNFLOWER ( Helianthus annuus L.) LEAVES ON THE GROWTH OF SELECTED WEEDS AND CROPS

GROWN SOLELY OR IN COMBINATION Mohammad Cholid

Indonesian Tobacco and Fibre Crops Research Institute

ABSTRACT

The study was conducted with the following objectives: to determine the effect of

incorporating common sunflower leaves in the soil on the growth and development of

itchgrass [Rottboellia. cochinchinensis (Lour)W.D. Clayton], barnyardgrass (Echinochloa

glabrescens Munro ex Hook.f.), water purslane [Ludwigia octovalvis (Jacq.) Raven],

mungbean (Vigna radiata L.), and rice (Oryza sativa L.). Treatments were replicated 3

times and laid out using randomized complete block design. Treatments were species of crops/weeds: 1) rice; 2) barnyardgrass; 3) water purslane; 4) rice + barnyardgrass; 5) rice

+ water purslan; 6) mungbean; 7) itchgrass ; and 8) mungbean + itchgrass. The Result

indicated that incorporation of common sunflower leaves significantly inhibited the

emergence of itchgrass, barnyardgrass, and water purslane, slightly inhibited that in rice,

while there was no effect in mungbean. Plant height, shoot and root dry weight and grain

yield of itchgrass and water purslane decreased significantly with incorporation of

common sunflower leaves over those of untreated. The incorporated leaves significantly

delayed days to flowering in most of the test species, except barnyardgrass. Incorporated

common sunflower leaves in the soil had inhibitory potential on water purslane and

itchgrass, but less or no inhibition on rice and mungbean. In contrast, common sunflower

leaves may be used for effective itchgrass and water purslane controls, without damaging

mungbean and rice plants. Key word: Allelopathic, Helianthus annuus L, crops, weeds

ABSTRAK

Pengaruh lama pencampuran residu daun bunga matahari (Helianthus annuus L.) dalam tanah pada pertumbuhan beberapa tanaman dan gulma

monokultur dan tumpangsari.

Penelitian ini bertujuan untuk mengevaluasi pengaruh lama pencampuran residu dari daun tanaman bunga matahari dengan tanah terhadap pertumbuhan Rottboellia cochinchinensis (Lour) W.D. Clayton, Echinochloa glabrescens Munro ex Hook.f., Ludwigia octovalvis (Jacq.) Raven, kacang hijau (Vigna radiata L.), dan padi (Oryza sativa L.). Rancangan Percobaan yang digunakan adalah Rancangan Acak Kelompok Faktorial, dengan 3 ulangan. Perlakuan meliputi: 1) padi; 2) Echinochloa glabrescens; 3) Ludwigia octovalvis; 4) padi + Echinochloa glabrescens; 5) padi + Ludwigia octovalvis; 6) kacang hijau; 7) itchgrass ; and 8) kacang hijau + itchgrass. Hasil percobaan menunjukkan bahwa pencampuran residu daun tanaman bunga matahari dapat menghambat perkecambahan gulma, sedikit menghambat pada padi, dan tidak menghambat pada kacang hijau. Tinggi tanaman, berat kering batang dan akar, serta produksi biji dari Ludwigia octovalvis dan Rottboellia cochinchinensis menurun secara nyata pada perlakuan residu dibanding dengan kontrol. Residu daun bunga matahari menunda saat pembungaan pada semua tanaman yang diuji, kecuali pada Echinochloa glabrescens. Hal

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ini menunjukkan bahwa residu daun dari tanaman bunga matahari efektif untuk mengendalikan gulma Ludwigia octovalvis, Rottboellia. Cochinchinensis, dengan tanpa menimbulkan kerusakan pada tanaman kacang hijau, serta sedikit penghambatan pada tanaman padi. Kata kunci : Alelopati, Helianthus annuus L, tanaman, gulma

Introduction

Most nations of the world face serious environmental problems, a portion of

which evolves from a heavy reliance on herbicides and pesticides for agricultural

production. Efforts toward a more sustainable form of agriculture must inevitably take

into account the adaptive mechanisms that have allowed success of certain plants, and

these include the allelochemicals they produce.

Allelopathy, particularly of crops, can play an important role in weed

management, if suitably managed and applied. A study conducted by Wilson and Rice

(1968) showed that common sunflower, Helianthus annuus L., possessed allelopathic

properties. Germinating sunflower seed reduced germination rate, shoot and radicle

length of weeds and seedling fresh weight of Trianthema portulacastrum L, Parthenium

hysterophorus L. and Amaranthus viridis L. weeds (Dharamraj, 1998). Dried sunflower

residues and leaf powder incorporated in the soil reduced the growth of sorghum,

soybean and sunflower itself (Irons and Burnside, 1982).

Natural phytotoxic chemicals from allelopathic plants can be exploited as novel

agrochemicals for controlling harmful weeds (Batish et al., 2001). Such chemicals not

only provide the desired results but also pose no threat to environment and have more

target sites in contrast to commercial herbicides. This study takes into consideration the

allelopathic effect of soil incorporated residues on the germination and further seedling

growth of selected major weeds and major staple grain crops

MATERIALS AND METHODS

Experiments were conducted from September 2003 to Februay 2004, at the

Central Experiment Station, Department of Agronomy, U.P. Los Baños, Philippines.

Mature seeds of itchgrass (R. cochinchinensis (Lour) W.D. Clayton), barnyardgrass

(Echinochloa glabrescens Munro ex Hook.f.), water purslane (Ludwigia octovalvis (Jacq.)

Raven) were collected from farms in Los Baños. Common sunflower (Helianthus annuus

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L.) and rice (Oryza sativa L.) var. PSB PC-74 seeds were obtained from the UPLB Central

Experiment Station, and mungbean (Vigna radiata L.) var. MG 50-10A seeds were

obtained from the Bureau of Plant Industry. All seeds were sun-dried and stored in a

closed container at Seed Storage prior to use.

Treatments were replicated 3 times and laid out using randomized complete block

design. Treatments were species of crops/weeds: 1) rice; 2) barnyardgrass; 3) water

purslane; 4) rice + barnyardgrass; 5) rice + water purslan; 6) mungbean; 7) itchgrass ;

8) mungbean + itchgrass. Lowland and upland soils collected from 0-15 cm depth from

a uniform location, at the Central Experiment Station, Department of Agronomy, U.P.

Los Baños, and each soil type was mixed thoroughly, and separately placed in 30 cm

diameter clay pots.

Preparation of plant residues, common sunflower plants grown at the UPLB

Central Experimental Station were harvested at the start of flowering. Common

sunflower leaves were cut and chopped into 2 to 3 cm pieces and uniformly

incorporated in respective pots. Concentration 1:16 (w/v) and 0 day duration (at

seeding) of incorporation of common sunflower leaves residues into soil were selected in

this study. One gram foliage residues for every 16 grams soil (1:16 w/w) was equivalent

to 312.5 g residues per 5000 g soil.

Foliage residues were incorporated in clay pots filled with soil, and 10 seeds of

test crops (rice and mungbean) and 20 seeds test weeds (itchgrass, barnyardgrass and

water purslane) were sown at the same time. Water was added to the pot to maintain the

soil at field capacity. The plants were kept under field condition at the Central

Experiment Station, Department of Agronomy, U.P. Los Baños, Philippines.

Seedlings were thinned to two per pot, and plants were watered as required.

Fertilizer at recommended rate for each crop was used. Fertilizer at 90-30-30 kg/ha of

N, P, K was applied in rice, barnyardgrass and water purslane pots. One third of N and

all P and K were applied basally at seeding. The remaining N was top-dressed at equal

splits at maximum tillering and panicle initiation stage of rice plant. While mungbean

and itchgrass pots were applied 20-40-40 kg/ha of N, P, K. All of fertilizer (N, P and K)

was applied basally at seeding.

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Azodrin (3 hydroxy-N-methyl crotonamide) 19.8 EC (2.0 kg ai/ha) insecticide

was applied to mungbean and rice plants at 14 DAS and 42 DAS to control leaf rollers

and leaf folders. No significant insect damage was observed during the experimental

period.

Three soil samples were taken and leaf residues were incorporated at 0 days

before sowing. Composite randomly collected samples were analyzed for pH, OM, total

N, available P, exchangeable K, and texture at the Department of Soil Science, University

of the Philippines Los Baños. Chemical and physical characteristics of mixed soil-foliage

residues incorporation are shown in Table 1.

Initial germination was observed three days after sowing to 14 days after sowing.

The germination was recorded when the radicle or hypocotyls were 2 cm in length, and

converted to percentage. Plant height was measured at two weeks intervals from

germination to maturity. Shoot and root length of the crops and weeds were measured

at the end of the experiment. Plant materials were dried at 800C for 48 hours in an oven

after which the dry weight was determined.

The F test of the RCBD was used to determine the significance among treatments

using analysis of variance. The F test showed significant results which was further

tested using LSD to evaluate the differences among treatment means.

Table 1. Chemical and physical characteristics of lowland and upland soil mixed with leaf of common sunflower used in Experiment.

CONSTITUENT LOWLAND UPLAND

Control 0 Control 0

pH 6.2 7.7 7.0 7.9 OM(%) 4.98 8.16 1.43 2.16 N(%) 0.24 0.32 0.08 0.06 P(ppm) 31.00 95.00 51.00 75.00 K(cmol/kgsoil) 0.83 12.7 0.74 8.4 Sand 13 24 Silt 33 36 Clay 55 39 Textural grade clay clay loam

RESULTS AND DISCUSSION

Seed Germination

Germination of rice, barnyardgrass, water purslane, and itchgrass was reduced

by common sunflower leaves incorporated in the soil, while germination of mungbean

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was not affected. There was no significant difference in seed germination among mono

and mixed cultures of all test species. Effect of common sunflower leaves on seed

germination of rice, mungbean, barnyardgrass, water purslane, and itchgrass are shown

in Table 2.

Leaves incorporated in the soil reduced the germination of rice seeds in both

mono and mixed cultures (Table 2). Germination of mungbean was not significantly

different among the treatments. This implies that mungbean was less sensitive crop

species to common sunflower leaves than rice. Germination of both rice and mungbean

was not affected by the culture (mono culture and mixed culture).

Table 2. Effect of incorporated common sunflower leaves on seed germination of rice, mungbean, itchgrass, barnyardgrass and water purslane in clay pots.

TEST PLANT GERMINATION (%)

Untreated Leaf Incorporation %Inhibition

Rice Rice 75.46a 61.46b 18.55 s Rice+Barnyardgrass 80.04a 61.46b 23.21 s Rice+W.purslane 75.78a 62.92b 16.97 s Barnyardgrass Barnyardgrass 75.00a 36.67b 51.11 s Rice+Barnyardgrass 86.67a 28.33b 67.31 s Water purslane Water purslane 67.03a 25.30b 62.26 s Rice+W.purslane 65.19a 22.60b 65.33 s Mungbean Mungbean 84.61a 71.35a 15.67 ns Mungbean+Itchgrass 82.11a 75.84a 7.64 ns Itchgrass Itchgrass 75.00a 33.33b 55.56 s Mungbean+Itchgrass 73.33a 28.33b 61.37 s

s = significant, ns = not significant Numbers followed by the same letters within test species are not significantly different at 5% LSD

Germination of the weed species (itchgrass, barnyardgrass and water purslane)

was significantly reduced by leaves incorporated in soil. Among the weed species, water

purslane showed the most inhibition, followed by barnyardgrass and itchgrass. This

indicated that water purslane was most sensitive to inhibitory substances present in

sunflower. These results are in agreement with earlier studies reported by Iron and

Burnside (1982) that weed seed germination and seedling growth was extract-species-

concentration-temperature dependent. Tongma et al. (1997) also reported that the

degree of inhibition on plant growth varied depending on plant species. Aqueous

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extracts of root and aboveground parts of sunflower significantly reduced germination

rate and percentage in tomatoes. The degree of reduction in germination was less in

maize. There were no significant effects on the germination and growth of soybean

(Beltran et al., 1997).

Plant Height

The height of rice, mungbean and barnyardgrass at 56 DAS were not

significantly reduced by common sunflower leaves incorporated in the soil (Table 3).

However, the heights of itchgrass and water purslane were significantly reduced.

Table 3. Effect of incorporated common sunflower leaves on plant height of rice, mungbean, itchgrass, barnyardgrass and water purslane at 56 DAS.

TEST PLANT PLANT HEIGHT (cm)

Untreated Leaf Incorporation % Inhibition (-)/ Stimulation (+)

Rice Rice 76.78a 74.77ab -2.62 ns Rice+Barnyardgrass 64.00b 64.93ab +1.45 ns Rice+W.purslane 74.63ab 74.80ab +0.23 ns Barnyardgrass Barnyardgrass 73.08a 66.75a -8.66 ns Rice+Barnyardgrass 69.32a 65.50a -5.51 ns Water purslane Water purslane 52.15a 13.47c -74.17 s Rice+W.purslane 34.50b 9.67c -71.97 s Mungbean Mungbean 36.48a 34.70a -4.88 ns Mungbean+Itchgrass 29.58a 32.17a +8.76 ns Itchgrass Itchgrass 119.30a 47.73b -59.99 s Mungbean+Itchgrass 100.95a 50.50b -49.98 s

s = significant, ns = not significant Numbers followed by the same letters within test species are not significantly different at 1% LSD

There was even slight stimulation in plant height of mixed culture rice (+1.45%)

+ barnyardgrass and rice (+0.23%) + water purslane when leaves were incorporated in

the soil as compared to the untreated. Conversely, slight inhibition in plant height

occurred in mixed culture barnyardgrass (-5.51%) when leaf residues were incorporated

in the soil. The magnitude of inhibition increased in mixed culture water purslane (-

71.97%) with leaves incorporated in the soil. The observed reduction of rice plant height

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in mixed culture rice + barnyardgrass compared to monoculture rice, may be due to

competition between rice and barnyardgrass.

Plant height of mungbean was not affected by common sunflower leaves in

mono and mixed culture with itchgrass. There was slight stimulation in plant height of

mixed culture mungbean when leaves were incorporated in the soil. Conversely,

inhibition of plant height in mixed culture itchgrass (-49.98%) with leaves incorporated

in the soil was observed. The significant reduction in itchgrass plant height in soil

incorporated with leaves over the untreated may be due to inhibitory substances present

in common sunflower leaves. Curtis and Coltam (1950) reported that sunflower

influences succeeding generations through decomposition and released of

allelochemicals from underground plant parts. Kaur (1998) also found that phytotoxic

compounds produced during sunflower biomass decomposition inhibited the

germination of pearl millet and greengram.

Rice plants were taller in the untreated than that when common sunflower leaves

were incorporated from 14 to 56 days after sowing (Figure 1).

0.00

20.00

40.00

60.00

80.00

100.00

120.00

140.00

14 28 42 56 70 84 98

Days after seeding

Pla

nt

he

igh

t (c

m)

Rice (C) Barnyardgrass (C)Rice/R+B (C) Barnyardgrass/R+B (C)Rice (R) Barnyardgrass (R)Rice/R+B (R) Barnyardgrass/R+B (R)

C = Untreated, R = Leaf incorporation, R+B = Mixed culture rice + barnyardgrass

Figure 1. Plant height of rice and barnyardgrass in mono and mixed cultures

from 14 DAS until 98 DAS.

There was no significant difference in rice plant height at 70 DAS to 98 DAS. This can be

attributed to the fact that common sunflower leaves may have different effects,

depending on the stages of residue decomposition and stage of growth and

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development of test plants. Inhibition effects of leaves of common sunflower on rice

growth were observed at the initial decomposition of leaves and decreased through

time.

From 84 to 98 DAS, rice plant height was constant. This may be due to the

transformation of the rice from vegetative to reproductive phase. Rice flowered at 72 to

84 days after seeding (Table 4). The height of rice plant was greater in the monoculture

than in mixed culture rice with barnyardgrass both in untreated plant and in the

treatment where leaves were incorporated. This may be attributed to the inter-specific

competition between rice and barnyardgrass. The same trend was shown in

barnyardgrass, where the height of barnyardgrass was greater in untreated compared to

the treated where leaves were incorporated in both mono and mixed culture.

Water purslane plants were taller in the untreated than in those where leaves

were incorporated from 14 DAS to 70 DAS (Figure 2). The same trend was observed in

the mono and mixed cultures. From 84 to 98 DAS there were no significant differences in

height observed. This result collaborates the finding of Narwal et al. (1999b) who

reported that the phytotoxicity of sunflower biomass persisted in the soil up to 9 weeks

after soil incorporation. The harmful allelochemicals might have either decomposed by

soil microflora or adsorbed in soil complexes. The decomposition rate of toxic

substances was fastest in the beginning of incubation and decreased with time and

become constant at later stages. Sunflower residues incorporated in the soil were most

harmful to the following crop up to 30 DAS, moderate up to 60 DAS and least at 90 DAS.

Most of the allelochemicals might have been released during the fast rate of residue

decomposition in the early stage of incorporation.

Tongma et al. (1997) reported that water extract of Mexican sunflower [Tithonia

diversifolia (Hemsl.) A. Gray] applied in soil inhibited root growth of the plant tested but

this inhibitory activity declined as it stayed longer in the soil. Kitou and Yoshida (1998)

also observed that lettuce germination and radicle elongation were inhibited by soil

extracts amended with leaves of Solidago altissima during early period of incubation,

although the inhibitory effects disappeared with an increase in the duration of

incubation period.

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0.00

20.00

40.00

60.00

80.00

100.00

14 28 42 56 70 84 98

Days after seeding

Pla

nt

he

igh

t (c

m)

Rice (C) Water Purslane (C)Rice/R+W (C) Water Purslane/R+W (C)Rice (R) Water Purslane (R)Rice/R+W (R) Water Purslane/R+W (R)

C = Untreated, R = Leaf incorporation, R+W = Mixed culture rice + water purslane

Figure 2. Plant height of rice and water purslane in mono and mixed cultures

from 14 DAS until 98 DAS.

Kobayashi (1998) reported that incorporation of dry Mexican sunflower leaves

into soil at the rate of 1 and 2% (w/w) inhibited the growth of rice seedlings. The

phytotoxic activity of incorporated leaf residue diminished 4 weeks after treatment of

soil. It was suggested that the decrease in allelopathic activity of Mexican sunflower

residues with time was due to action of soil microorganisms and soil adsorption of the

active components.

Mungbean plant height was not significantly different in the untreated and the

treatment where leaves were incorporated in the soil. Itchgrass was taller in untreated

than that grown in soil where common sunflower leaves were incorporated from 14

DAS until last stage of growth (Figure 3). Mungbean established first before itchgrass

due to its less sensitivity to leaf residues. Itchgrass, however, was significantly inhibited

by common sunflower leaves.

10

0.00

20.00

40.00

60.00

80.00

100.00

120.00

140.00

14 28 42 56 70 84 98

Days after seeding

Pla

nt

he

igh

t (c

m)

Mungbean (C) Itchgrass (C) Mungbean/M+I (C) Itchgrass/M+I (C)

Mungbean (R) Itchgrass (R) Mungbean/M+I (R) Itchgrass/M+I (R)

C = Untreated, R = Leaf incorporation, M+I = Mixed culture mungbean + itchgrass

Figure 3. Plant height of mungbean and itchgrass in mono and mixed cultures

from 14 DAS until 98 DAS.

The inhibitory effect of common sunflower leaves may be due to the presence of

allelochemicals. Several workers (Curtis and Coltam, 1950; Rice, 1983; Leather, 1983;

Narwal et al., 1999a) reported that sunflower influences succeeding crops through

decaying and exudates from above and underground plant parts. Rice (1983) and

Leather (1983) also reported that sunflower can have negative effects on successive crops

due to its strong allelopathic effect. Phenolics were thought to be responsible for such

behavior (Einhellig, 1986).

Days to Flowering

Days to flowering of most test plants were affected by incorporated leaves of

common sunflower. Table 4 presents the effect of the leaves on days to flowering of the

test species.

As indicated in Table 4, days to flowering of all test species except barnyardgrass

were delayed in treatment with leaves of common sunflower. Days to flowering of

barnyardgrass was not affected by leaves incorporated in the soil. Again here,

inhibitory substances in leaves of common sunflower exert some selectivity on

barnyardgrass.

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Table 4. Effect of incorporated common sunflower leaves on days to flowering of rice, mungbean, itchgrass, barnyardgrass and water purslane.

TEST PLANT DAYS TO FLOWERING (DAS)

Untreated Leaf Incorporation

Rice Rice 73.67b 83.33a Rice+Barnyardgrass 72.67b 81.33a Rice+Water purslane 72.00b 82.00a Mungbean Mungbean 35.67b 41.67a Mungbean+Itchgrass 32.33b 41.33a Itchgrass Itchgrass 34.33b 43.33a Mungbean+Itchgrass 34.33b 42.33ab Barnyardgrass Barnyardgrass 42.67a 42.00a Rice+Barnyardgrass 40.67a 42.00a Water purslane Water purslane 34.00ab 40.67a Rice+Water purslane 32.00b 39.33a

Number followed by the same letters within test species are not significantly different at 1% LSD

This result is in agreement with that of Narwal et al. (1999a) reported that

common sunflower leaves through decomposition released allelochemicals that

inhibited seed germination, further growth and development rate of plant such as

extended days of flowering. Addition of 2 g residues to 80 g of soil significantly delayed

seed emergence, depression in growth, and reduced sorghum dry weight (Schon and

Einhellig, 1982). Akemo et al. (2000) found that rate of flowering and fruit set of tomato

plants varied directly with the proportion of rye to pea in the cover crop, and decreased

with increased rye to pea proportion. Kohli et al. (1998) also reported that

allelochemicals act via bringing certain changes in physiological functions, such as

respiration, photosynthesis and ion uptake. These, in turn, result in visible changes in

seed germination, and further reductions in growth and overall performance of the

target plants.

Shoot Dry Weight

The effect of incorporated common sunflower leaves on shoot dry weight of rice,

mungbean, itchgrass, barnyardgrass and water purslane at harvest is presented in

Table 5. As shown in Table 5, rice shoot dry weight in monoculture (+ 32.32%) was

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significantly increased in the treatment with leaves compared to the untreated. Highest

shoot dry weight of rice was attained in monoculture rice (14.74 g/plant) with common

sunflower leaves incorporated in the soil, but was not significantly different from that in

the mixed culture with barnyardgrass.

Table 5. Effect of incorporated common sunflower leaves on shoot dry weight of rice, mungbean, itchgrass, barnyardgrass and water purslane at harvest.

TEST PLANT SHOOT DRY WEIGHT(g/plant)

Untreated Leaf Incorporation % Inhibition (-)/ Stimulation (+)

Rice Rice 11.14b 14.74a +32.32 s Rice+Barnyardgrass 4.05c 4.33c +6.91 ns Rice+W.purslane 12.21ab 13.94ab +14.17 ns Barnyardgrass Barnyardgrass 20.32a 18.82a -7.38 ns Rice+Barnyardgrass 18.49a 17.33a -6.27 ns Water purslane Water purslane 10.50a 8.29b -21.05 s Rice+W.purslane 4.73c 2.76d -41.65 s Mungbean Mungbean 3.28a 2.81ab -14.33 ns Mungbean+Itchgrass 1.87c 2.33bc +24.60 ns Itchgrass Itchgrass 5.41a 3.87b -28.47 s Mungbean+Itchgrass 2.38c 1.52c -36.13 ns

s = significant, ns = not significant Numbers followed by the same letters within test species are not significantly different at 5% LSD

Among the untreated (mono and mixed culture of rice and barnyardgrass), rice

shoot dry weight was lowest when rice was made to compete with barnyardgrass. Rice

shoot dry weight was not affected by the leaves incorporated in the mixed culture with

water purslane or barnyardgrass. However, leaves of common sunflower incorporated

in soil reduced shoot dry weights of water purslane in mono (-21.05) and mixed culture

(-41.65).

Stimulation in shoot dry weight of rice in mono but not in the mixed culture was

observed when leaves were incorporated in the soil compared to untreated. The

difference in stimulation in rice shoot dry weight in mixed cultures of barnyardgrass

and water purslane probably due to the greater competition ability of barnyardgrass

than water purslane against rice. Conversely, inhibition of shoot dry weight was

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observed in mixed culture barnyardgrass (-6.27%) and mixed culture water purslane (-

41.65%) as companion crops of rice.

As in barnyardgrass and water purslane significant reduction in itchgrass shoot

dry weight was recorded when leaves were incorporated in the soil. The stimulation in

shoot dry weight of rice in monoculture could be due to the residues being source as

organic matter. Soil amendment of straw as a supply of organic matter had been

reported by Taja and Zaag (1986), and Schmidit (1982). Narwal et al. (1999) reported that

57.1% organic carbon from the sunflower shoot was mineralized/decomposed in 9

weeks.

The degree of inhibition on plant growth varied depending on test species. At 56

DAS and beyond, it was observed that leaves incorporated in the soil did not adversely

affect the growth of rice and barnyardgrass, but were still inhibitory to itchgrass and

water purslane. However, incorporated leaves did not affect rice when grown with

barnyardgrass or water purslane. Mungbean shoot dry weights were not affected by

incorporated leaves in both mono and mixed culture with itchgrass. While, leaf residues

of sunflower reduced shoot dry weights of itchgrass in monoculture. Shoot dry weight

of itchgrass was reduced in the monoculture but not in the mixed culture.

Root Dry Weight

Rice root dry weights with common sunflower leaves incorporated in the soil

were not significantly different from those of untreated (Table 6). Monoculture and

mixed culture rice with barnyardgrass or water purslane were not affected by

incorporated leaves. Likewise barnyardgrass root dry weight in mono or mixed culture

was not significantly changed by leaf incorporation. Only water purslane root dry

weight in mono or mixed culture, and itchgrass in monoculture were significantly

reduced by the incorporated leaves of common sunflower.

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Table. 6. Effect of incorporated common sunflower leaves on root dry weight of rice, mungbean, itchgrass, barnyardgrass and water purslane at harvest.

TEST PLANT ROOT DRY WEIGHT(g/plant)

Untreated Leaf Incorporation % Inhibition (-)/ Stimulation (+)

Rice Rice 4.61a 5.51a +19.52 ns Rice+Barnyardgrass 0.99b 1.39b +40.40 ns Rice+W.purslane 3.87a 5.10a +31.78 ns Barnyardgrass Barnyardgrass 25.45a 23.23a -8.72 ns Rice+Barnyardgrass 24.28a 22.24a -8.40 ns Water purslane Water purslane 2.27a 2.02b -11.01 s Rice+W.purslane 0.73c 0.42d -42.47 s Mungbean Mungbean 0.53a 0.45a -15.09 ns Mungbean+Itchgrass 0.16c 0.27b +68.75 s Itchgrass Itchgrass 2.32a 1.79b -22.84 s Mungbean+Itchgrass 1.27c 0.90c -29.13 ns

s = significant, ns = not significant Numbers followed by the same letters within test species are not significantly different at 5% LSD

In contrast to the shoot dry weight, root dry weight of rice monoculture was not

stimulated by the incorporation of leaves were incorporated in the soil. Great inhibition

of root dry weight (-42.47%) occurred in mixed culture of rice and water purslane as

compared to barnyardgrass (-8.40%). This suggests that water purslane was more

sensitive to the incorporated leaves of common sunflower than barnyardgrass.

Mungbean root dry weight in mixed culture was higher than the untreated when leaves

were incorporated in the soil. Root dry weight of itchgrass in monoculture was

significantly reduced.

There was stimulation in root dry weight of mungbean mixed culture (+68.75%)

when leaf residues were incorporated in the soil as compared to the untreated. While,

itchgrass shoot dry weight on mixed culture was slightly inhibited. It may be inferred

that inhibitory effects of common sunflower leaves on weed species may eliminate

competition between mungbean and itchgrass, and may give favorable growth

condition to the crop.

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Incorporated leaves of common sunflower reduced the germination, plant

height, and dry matter accumulation in weed species. This may be due to presence of

phytotoxic allelochemicals in the sunflower infested soil. These results collaborate the

findings of Wilson and Rice (1968), Nanjappa et al. (1998) and Narwal (1999). Park (1991)

also indicated that sunflower exudates reduced fresh weight of radish, and E. colona by

23% and 17% respectively, the fresh weight of rice was not affected.

Abeysekera (1992) also reported that residues of both wild sunflower [Tithonia

diversifolia (Herm SL.) Gray] and common sunflower [Helianthus annuus (L.)]

significantly inhibited germination, seedling growth, and reduced fresh weight, and dry

weight of E. colona, but no inhibitory effects on rice plants. Sandhu (1997) reported that

in the field the preceding sunflower crop decreased the plant height and forage or grain

yields of all crops, however, inhibition was maximum in greengram, maize and sesame

and minimum in rice and cowpea.

Grain Yield

Grain yield of rice and mungbean whether in mono or mixed cultures with the

weeds were not affected significantly by the incorporated leaves of common sunflower.

However, the seed yield of water purslane in both mono and mixed culture with rice

and itchgrass in mixed culture with mungbean was reduced (Table 7). Higher grain

yield was attained in monoculture rice (15.75 g/plant) with leaves incorporated in the

soil, but was not significantly different from that of the untreated. Seed yield of

barnyardgrass whether in mono or mixed culture with rice was not affected by the

incorporated leaves in mono and mixed culture with rice.

The magnitude of inhibition was greater in water purslane mixed culture with

rice than in the monoculture. The significant reduction in seed grain yield of water

purslane suggests inhibitory substances present in common sunflower leaves. The

observed reduction in water purslane seed yield due to the incorporated leaves of

common sunflower, reduced competition, increasing available growth factor such as,

water, soil nutrients, and light for the rice crop. The stimulation of grain yield of rice

though not significant could be due to the residues serving as source organic matter.

Soil amendment with straw as a supply of organic matter had been reported by Taja and

Zaag (1986), and Schmidit (1982).

16

Table 7. Effect of incorporated common sunflower leaves on grain seed yield of rice, mungbean, itchgrass, barnyardgrass and water purslane

TEST PLANT GRAIN SEED YIELD (g/plant)

Untreated Leaf Incorporation % Inhibition (-)/ Stimulation (+)

Rice Rice 12.90ab 15.75a +22.09 ns Rice+Barnyardgrass 4.40c 3.91c -11.14 ns Rice+W.purslane 11.42b 13.68ab +19.79 ns Barnyardgrass Barnyardgrass 6.19a 5.96a -12.44 ns Rice+Barnyardgrass 5.72a 6.17a +7.87 ns Water purslane Water purslane 7.03a 6.28b -10.67 s Rice+W.purslane 4.05c 1.79d -55.80 s Mungbean Mungbean 1.84a 1.81a -1.63 ns Mungbean+Itchgrass 1.40a 1.76a +25.71 ns Itchgrass Itchgrass 5.44a 4.05ab -25.55 ns Mungbean+Itchgrass 5.29a 3.06b -42.16 s

s = significant, ns = not significant Numbers followed by the same letters within test species are not significantly different at 5% LSD

Seed yield of rice in mixed culture rice + barnyardgrass (3.91 g/plant) was

significantly lower than that in mixed culture rice + water purslane (13.68 g/plant). This

suggests that barnyardgrass was more competitive to the rice as compared to water

purslane. Itchgrass seed yield in mixed culture with mungbean was highly reduced by

incorporated leaves of common sunflower. There was slight stimulation in grain yield of

mixed culture mungbean (+25.71%) but not significant when leaves were incorporated

in the soil as compared to the untreated.

Common sunflower leaves incorporated in the soil inhibited the germination of

most test plants except mungbean, but proved very slightly stimulatory to further

growth of rice. This indicates that comparatively, mungbean and rice were more tolerant

than the test weeds to the allelochemicals present in sunflower infested soil. These

results are in agreement with previous studies reported by Narwal et al. (1999a) that

preceding sunflower crop decreased the plant height, dry matter and yield of all

subsequent test crops as compared to those sown in fallow plots. Maximum reduction in

growth (plant height, dry matter), yield attributes and grain/fodder yield was observed

17

in cotton and sunflower, minimum in cereals (sorghum, pearlmillet, maize) and

moderate in legumes (clusterbean, cowpea, greengram) (Narwal et al.,1999a).

In soil incorporation of leaf extracts of common sunflower, abiotic (physical and

chemical) and biotic (microbial) soil barriers can limit the phytotoxicity of chemical in

terms of quality and quantity required to cause injury. Organic matter, reactive mineral

surfaces, ion exchange capacity, inorganic ions, and abiotic and biotic factors of soil

environment significantly influence allelochemical activity (Inderjit, 2000). Beltran (1997)

observed that allelopathic effects are difficult to ascertain in nature owing to the

difficulty of separating them from other factors (edaphic, climatic, and competition for

water, light and nutrients). Even in the absence of microbial metabolism, soil renders

compounds much less toxic than they are in laboratory solutions. This reduced toxicity

is due to slow diffusion rate and to formation of various complexes and sorptive

reactions in soil. Schmidt (1999) found that even extremely toxic compounds like 2,5-

dinitrophenol is much less toxic in soil than in laboratory bioassays.

Identification of chemicals in sunflower done by Dharamraj (1998) indicated that

phenolics are responsible for the observed interference in nature and are potent

allelochemicals. He suggested that the allelopathic effect of sunflower leaf litter is due to

presence of phenolic acids viz., p-coumaric, vanillic, syringic, p-hydroxybenzoic and

ferulic. Phenolic acids are released into soil by plants as decomposition metabolites and

in some plants as root exudates or leaf leachates (Cecchi et al., 1999). These chemicals

are involved in several soil processes, including the formation of humus, nutrient

availability, dissolution of minerals and allelopathy. Gogoi et al. (2000) reported that

phenols are common secondary plant metabolites involved in such phytotoxic activity,

as they occur in higher concentrations in plant tissues and soil. The phenolic acids affect

seed germination, radicle and plumule elongation and dry matter accumulation in many

crop species.

The stimulation of growth in the test plants could be due to the common

sunflower residues serving as source of organic matter. Soil amendment of straw as a

supply of organic matter had been reported by Taja and Zaag (1986), and Schmidit

(1982). These workers pointed out that upon decomposition, proteins, nucleic acids and

nitrogenous substances were converted to NO3- which would be utilized by the plant.

18

This phenomenon may explain the observation in monoculture rice with incorporated

leaves in the soil, that shoot growth of rice was stimulated. This result collaborates the

finding of Narwal et al. (1999b) who reported that the phytotoxicity of sunflower

biomass persisted in the soil up to 9 weeks after soil incorporation, then the harmful

effect decreased with passage of time. In 9 weeks, 57.1% organic carbon from the

sunflower shoot was mineralized/decomposed.

Debnath and Hajara (1972) found that soil treated sesbania also increased other

soil nutrients but it maintained the same pH as that of control. The present results are

agreement with the previous investigations as reported by Nagarajah and Nizar (1982).

One ton of fresh wild sunflower leaves and tender stem is capable of providing about 5

kg N, 1 kg P2O5, 10 kg k2O. Application of inorganic fertilizer can be appreciably

reduced when it is applied with green manure.

CONCLUSION

Incorporation of common sunflower leaves significantly inhibited the emergence

of itchgrass, barnyardgrass, and water purslane, slightly inhibited that in rice, while

there was no effect in mungbean. Plant height, shoot and root dry weights and grain

yield of itchgrass and water purslane decreased significantly with incorporation of

common sunflower leaves over those of the untreated.

Mungbean and barnyardgrass were less affected by leaf incorporation, while rice

was slightly affected. The slight enhancement of growth in rice may be due to the

organic matter coming from the incorporated leaves. Incorporated common sunflower

leaves in the soil had inhibitory potential on water purslane and itchgrass, but less or no

inhibition on rice and mungbean. It may be inferred that common sunflower leaves may

be used for effective itchgrass and water purslane controls, without damaging

mungbean and rice plants.

19

LITERATURE CITED

ABEYSEKERA, S.K. M.M.A. 1992. comparative study on agronomic characters and allelopathic activity of common sunflower (Helianthus annuus L.) and wild sunflower (Tithonia diversifolia (Herm SL.) Gray). MS Thesis . University of the Philippines at Los Baños. Philippines. 71p.

AKEMO, M.C., BENNETT and E.E. REGNIER. 2000. Tomato growth in spring-sown cover crops. Hortscience 35:843-848.

ALIOTTA, G. 1998. Localization of action site(s) of allelochemicals in seeds: Implications for weed control. In Abstracts. Allelopathy Journal 6(2).pp 281-282.

AN, M., I.R. JOHNSON and J.V. LOVETT. 1996. Mathematical modeling of allelopathy. I. Phytotoxicity caused by plant residues during decomposition. Allelopathy Journal 3 (1): 281-282.

______, J. PRATLEY and T. HAIG. 1998. Allelopathy: from concept to reality. Proceeding of the 9th Australian Agronomy Conference, Wagga wagga. pp. 1-5.

ANAYA, A.L. and H.R. PELAYO-BENAVIDES. 1997. Allelopathic potential of Mirabilis jalapa L. (Nyctaginaceae): Effects on germination, growth and cell division of some plants. Allelopathy Journal 4: 57-68.

BARANOV, V.I. 1980. Interaction of Phenolic compounds with metallic ions in regulation of growth. Sov. Plant Physiol. 27:805-811.

BATISH, D.R., H.P. SINGH and R.K. KOHLI. 2001. Allelopathy as a tool for sustainable weed management. The Proceeding of the 18th Asian-Pacific Weed Science Society Conference. May 28- June 2, 2001. Beijing, P.R. China. pp. 168-173.

___________, P. TUNG, H.P. SINGH and R.K. KOHLI. 2002. Phytotoxicity of sunflower residues against some summer season crops. J. Agronomy and Crop Science 188, 19-24.

BELL, D.T. and KOEPPE. 1972. Non competitive effects of giant foxtail on growth of corn . Agron. J. 64:321-325.

BELTRAN, L., LEYVA, A. and L. CAPARICON. 1997. A preliminary study of the allelopathic effect of sunflower (Helianthus annuus L.) on several economic crops. Cultivos Tropicales 18(1): 40-42.

BERES, I., SARDI, K. and S. KAMAN. 1998. Allelopathic effect of Ambrosia artemisifolia L. on germination and seedling growth of field crops.In Abstracts. Allelopathy Journal 6(2).pp 288.

_________ and G. KAZINCZI. 2000. Allelopathic effects of shoot extracts and residues of weeds on field crops. Allelopathy Journal 7(1): 93-98.

20

CHEEMA, Z.A. and KHALIQ. 2000. Use of sorghum allelopathic properties to control weeds in irrigated wheat in a semi arid region of Punjab. Agriculture, Ecosystem and Environment 79:105-112.

CECCHI, A.M., KOSKINEN, W.C., HAIDER, K. and H.H. CHENG. 1999. Effect of soil properties on sorption of phenolic acids to soil. In Abstracts. Allelopathy Journal 7(1).pp. 164.

COCHRAN, V.L., L.F. ELLIOTT and R.I. PAPENDICK. 1977. The production of phytotoxins from surface crop residues. Soil Sci. Soc. Am. J. 41:903-908.

COLTON, C.E. and F.A. EINHELLIG. 1980. Allelopathic mechanisms of velvetleaf (Abutilon theoprasti Medic., Malvaceae) on soybean. Am. J. Bot. 67: 1407-1413.

CONNOR, D.J. and A.J. HALL. 1997. Sunflower physiology. In : SCHNEITER, A.A. (ed.), Sunflower technology and production, Monograph No. 35, pp. 113-182. CSSA, Madison.

CRONJE, J.I., RETHMAN, N.F.G. and C.F. REINHARDT. 1999. Towards understanding, crop reactions to mulching and relative importance of allelopathy. In Abstracts. Allelopathy Journal 7(1).pp 118.

CRUZ-ORTEGA, R., A.L. ANAYA, B.E. HERNANDEZ-BAUTISTA and G. LAGUNA-HERNANDEZ. 1998. Effects of allelochemicals stress produced by Sicyos deppei on seedling root ultrastrucutre of Phaseolus vulgaris and Cucurbita ficifolia. Journal of Chemical Ecology 24:2039-2057.

CURTIS, J.T. and G. COTTAM. 1950. Antibiotic and autotoxic effects in prairie sunflower. Bull. Torr. Bot. Club 77, 137-191.

DAKSHININI, K.M.M. and INDERJIT. 1999. Multifaceted approach in the study of allelopathy. In Abstracts, Allelopathy journal 7(1). pp116, 2000.

DHARMARAJ, G. 1998a. Allelopathic influence of sunflower on field crops. In abstracts. Allelopathy Journal 6(1).pp.103.

____________. 1998b. Influence of germinating seeds and seedlings of sunflower on weed spp. In abstracts. Allelopathy Journal 6(1).pp.112.

____________. 1998c. Identification of allelochemicals in sunflower. In abstracts. Allelopathy Journal 6(1).pp.114.

DAYAN, F.E., J.G. ROMAGNI, M.R. TELLEZ, A.M. RIMARDO and S.O. DUKE. 1999. Managing weeds with natural products. Pestic. Outlook. 5, 185-188.

DUKE, S.O., F.E. DAYAN, A. HERNANDEZ, M.V. DUKE and H.K. ABBAS. 1997. Natural products as leads for new herbicide mode of action. Proc. Brighton Crop Prot. Conf., Weeds. 2, 579-586.

EINHELLIG, F.A. and L. KUAN. 1971. Effects of scopoletin and chlorogenic acid on stomata aperture in tobacco and sunflower. Bull. Torrey Bot. Club 98 : 155-162.

21

___________ and M. L. STILLE. 1979. Effects of ferulic and p-coumaric acids on plant water status. Abstr. Bot. Soc. Am., Misc. Ser. Publ. 157:40-41

___________ and G.R. LEATHER. 1988. Potential for exploiting allelopathy to enhance crop production. Journal of Chemical Ecology 14: 1829-1844.

___________. 1996. Interactions involving allelopathy in cropping systems. Agron. J. 88, 886-893.

ESPINO, R.R.C. and C. S. ATIENZA. 2000. Crop diversification in the Philippines. Department of Horticulture, College of Agriculture, UP Los Baños, Laguna, Philippines.15p.

GOGOI, B., KAUSHIK DAS and K.K. BARUAH. 2000. Effcet of allelochemicals on germination and seedling growth of rice (Oryza zativa L.) cultivars. Allelopathy Journal 7 (2): 279-284.

GLASS, A.D.M. 1973. 1973. Influence of phenolic acids on ion uptake. Plant Physiology 51: 1037-1041.

GRUMMER, G. 1955. Die gegenseitige bonere pflanzen-allelopathie. In: THOMPSON, A.C. (ed). 1985. The Chemistry of allelopathy. ACS Symp. Series 268. Washington, D.C. 4, 34-54.

GUENZI, W.D. and Mc CALLA. 1966. Phenolic acids in oats, wheat, sorghum and corn residues and their phytotoxicity. Agron. J. 58:303-304.

HALL, A.B., U. BLUM and R.C. FITES. 1982. Stress modification of allelopathy of Helianthus annuus L. debris on seed germination. Amer. J. Bot.: 776-783.

HAO, X. and E. DE JONG. 1988. Growth of wheat and barley seedlings at different matric and osmotic potentials. Agronomy Journal 80: 807-811.

HEGDE, R.S. and D.A. MILLER. 1990. Allelopathy and autotoxicity in alfafa: characterization and effects of preceding crops and residue incorporation. Crop. Sci. 30, 1255-1259.

HWANG, S.J., D.H. SHIN and K.U. KIM. 1997. Identification of biologically active substance from lilac (Syringa vulgaris L.). Korean Journal of Weed Science 17: 334-344.

INDERJIT and K.M.M. DAKSHINI. 1998. Allelopathic interference of Chickweed (Stellaria media) with seedling growth of wheat (Triticum aesticum). Cananadian Journal of Botany 76: 1317-1321.

________. 2000. Soil: environmental effects on allelochemical activity. Agronomy Journal 93: 79-84.

IRONS, M.S. and C.V. BURNSIDE. 1982. Competitive and allelopathic effects of sunflower. Weed Science 30:372-377.

JANIYA, J.D. 2002. Yield losses, major weed species and suggested management systems in selected major crops [Rice (Oryza sativa L.)]. In Weed management in major crops of the Philippines. WSSP, Inc. CPAP, Inc. pp.17-37.

22

JUNG QUAN, YU. 1999. Allelopathic problems and research in vegetable production. Advances in Horticulture 2: 336-343.

KALITA, D., H. CHOUDHARY and S.C. DEY. 1999. Assessment of allelopathic potential of some common upland rice weed species on morpho-physiological properties of rice (Oryza sativa L.) plant. Crop research 17: 41-45.

KIMBER, R.W.L. 1973. Phytotoxicity from plant residues. II. The effect of time of rotting of straw from some grasses and legumes on the growth of wheat seedlings. Plant Soil 38: 347-361.

KITOU, M. and S. YOSHIDA. 1998. Allelopathic effects of extracts of soil amended with some plant materials on germination and radicle elongation of lettuce. Journal of Weed Science and Technology 43: 1-9.

KOBAYASHI, K. 1998. Allelopathic activity of Mexican sunflower (Tithonia diversifolia) in soil. Weed Science 46: 432-437.

KOEPPE, D. E., L. M. ROHRBAUGH, E. L. RICE and S.H. WENDER. 1970. Tissue age and caffeoylquinic acid concentrations in sunflower, Phytochemistry 9:297-301.

KOHLI, R.K., D. BATISH and H.P. SINGH. 1998. Allelopathy and its implications in agroecosystems. Journal of Crop Production. 1: 169-202.

KOHLI, R.K. and PARIANA. 1992. Allelopathic impact of sunflower on crops. In Proceedings. National Symposium Allelopathy in Agroecosystems. TAURO, P. and S.S. NARWAL (eds). Hisar India : Indian Society of Allelopathy. pp. 29-30.

PARK, K.H. 1991. Allelopatic activity and potential natural herbicide from sunflower (Helianthus annuus L.). Ph.D Dissertation. University of the Philippines at Los Baños. Philippines. 132p.

LEATHER, G.R. 1983. Sunflowers (Helianthus annuus) are Allelopathic to weeds. Weed Science. 31:37-42.

LEE, C.W., Y.W. KIM and B.C. KOO. 1997. Influence of light, osmotic potential, pH and rice straw mulching on growth of barley (Hordeum vulgare L.) and water foxtail (Alopecurus aequalis var. amurensis (kom) Ohwi). Korean Journal of Weed Science 17:310-313.

LIN, W.X., K.U. KIM and D.H. SHIN. 2000. Rice allelopathic potential and its modes of action on barnyardgrass (Echinochloa crus-galli). Allelopathy journal 7(2): 215-224.

LOVETT, J.V. 1989. Phytochemical ecology: allelochemicals, mycotoxins and insect pheromones and allomones. CHOU, C.H. and G.R. WALLER (eds). Taipei. ROC. Pp. 49-67.

___________. 1990. Allelopathy and self defense in Barley. In BASSET, C., L.S. WHITEHOUSE and J.A. ZABKIEWIZZ (eds). Alternatives to chemical control of weeds. Rotorua, New Zealand. pp. 57-65.

23

MACIAS, F.A. 1995. Allelopathy in the search for natural herbicide model. In Inderjit, DAKSHINI, K.M.M. and F.A. EINHELLING (eds).. Allelopathy, organisms, processes, and applications. ACS Symp. Series 582.Washington, DC, 23, 310-329.

___________, A. TORRES, J.M.G. MOLINILLO, R.M. VARELLA, and D.

CASTELLANO. 1996. Potential allelopathic sesquiterpene lactones from sunflower leaves. Peredovick. Pergamon. Phytochemistry, 43 : 1205-1215

___________, ROSA M. VARELA, ASCENSION and JOSE MARIA G. MOLINILLO. 1993. Potential allelopathic guainolides from cultivar sunflower leaves, var. SH-222. Peredovick. Pergamon. Phytochemistry, 34 : 669-674.

___________, J.M.G. MOLINILLO, R.M. VARELA, A. TORRES and R.O. TRONCOSO. 1998. Allelocemicals in: OLOFDOTTER, M. (ed). 1998a. Allelopathy in Rice. International Rice Research Institute (IRRI). pp.69-79.

___________, R.M. OLIVA, A.M. SIMONET and J.C.G. GALINDO. 1998b. What are allelocemicals? in: implications for crop and soil management in agroecosystems. In Abstracts. Allelopathy Journal. 6(2).pp.301.

___________, OLIVA, R.M., VARELLA, R.M., TORRES, A. and MOLINILLO, M.G. 1999. Allelochemicals from sunflower leaves cv. Peredovick. Pergamon. Phytochemistry, 52 : 613-621.

MALLIK, M.A.B. 1999. Allelopathy and nitrogen fixation in legumes. In Abstracts. Allelopathy Journal 7(1).pp 120.

MANDAVA, N.B. 1985. Chemistry and biology of allelopathic agent. In : THOMPSON,

A.C. (ed).1985. The Chemistry of allelopathy. ACS Symp. Series 268. Washington, DC, 4: 34-54.

MOODY, K. 1986. A literature review of weeds in grain legumes in the Philippines. Philipp. J. Weed Sci. 13: 19-27.

MOLISH, H. 1937. Der Einflusslinear pflanze aufdie audere-Allelopathie; In:THOMPSON (ed). 1985. The Chemistry of allelopathy. ACS Symp. Series 268 Washington, D.C.4: 34-54.

MULLER, C.H. 1971. Biochemical interactions among plants. National Academy of Sciences, Washington, D.C. pp. 64-72.

MURPHY, D.J.B. and T.L. NOLAND. 1982. Temperature effects on seed inhibition and leakage mediated by viscosity and membranes. Plant Physiology 69:428-431.

NAGARAJAH, S. and B.M. NIZAR. 1982. Wild sunflower (Thithonia diversifolia) green manure for rice in the mid country wet zone. Tropical agriculturist 138:69-79.

NANJAPPA, H.V., R. POONGUZHALAN and B.K. RAMACHANDRAPPA. 1999. Influence of sunflower on subsequent crops. Allelopathy Journal 6: 69-74.

24

NARWAL, S.S., M.K. SARMAH and D.P.S. NANDAL. 1997. Allelopathic effects of wheat residues on growth and yield of fodder crops. Allelopathy Journal 4:111-120.

_____________, YADAVA, S. and S. GUPTA. 1999a. Allelopathic effects of sunflower on succeeding summer crops. 1. Field studies and bioassays. Allelopathy Journal 6:35-48.

_____________, T. SINGH, J.S. HOODA and M.K. KATHURIA. 1999b. Allelopathic effects of sunflower on succeeding summer crops. 2. Pot culture and biomass decomposition. Allelopathy Journal 6:209-226.

NAVAREZ, D.C. and R.P. ROBLES. 2002. Yield losses, major weed species and suggested management systems in selected major crops (Field legumes). In Weed management in major crops of the Philippines. WSSP, Inc. CPAP, Inc. pp. 42-44.

NYARKO, K.A. and S.K. DE DATTA. 1991. A handbook for weed control in rice. International Rice Research Institute (IRRI). Philippines. 113 p.

PALLER, E.C. 2002. Yield losses, major weed species and suggested management systems in selected major crops [Corn (Zea mays L.)]. In Weed management in major crops of the Philippines. WSSP, Inc. CPAP, Inc. pp. 38-41.

PANCHO, J.V. 1991. Grassy weeds in the Philippines. In Baker, F.M.G. and P.J. Terry: Tropical grassy weeds. CAB International for Casafa. Report Series 203,pp. 183-188.

PATTERSON, D.T. 1981. Effects of allelopathic chemicals on growth and physiological responses of soybean (Glycine max). Weed Sci. 29:53-58.

PAWAR, K.B. and P.D. CHAVAN. 1999. Influence of leaf leachates of plant species on mineral nutrition of Sorghum bicolor (L.) Moench. Allelopathy Journal 6: 87-92.

PURVIS, C.E. and G.P.D. JONES. 1990. Differential response of wheat to retain crop stubbles. II. Other factors influencing allelopathic potential; intraspecific variation, soil type and stubble quantity, Aust. J. Agric. Res. 41, 243-25 2.

PUTNAM, A.R. 1994. Phytotoxicity of plant residues. In: UNGER, P.W. (ed.), Managing Agricultural Residues, CRC Press, New York. pp. 285-314.

REHMAN, A. 1998. Allelopathic potential of Parthenium hysterophorus Linn. On germination, growth and dry matter production in Cassis sophera Linn. Bionature 18(1): 17-20.

REIGOSA, M.J., A.M. SANCHEZ-MOREIRAS and O. WEISS. 1999. Interacting factors in the manifestation of allelopathic effects. In abstracts Allelopathy Journal 7(1).pp 118.

_________, L. GONZALES, A. SANCHES-MOREIRAS, B. DURAN, D. PUIME, D. A. FERNANDEZ and J.C. BOLANO. 2002. Comparison of physiological effects of allelochemicals and commercial herbicides. Allelopathy journal 8(2): 211-220.

25

RICE, E.L. and S.K. PANCHOLY. 1973. Inhibition of nitrification by climax ecosystems II. Additional evidence and possible role of tannins. American Journal of Botany 60:691-720.

_________. 1974. Allelopathy. Academic Press, New York. 353 p.

_________, C.Y. LIN and C.Y. HUANG. 1981. Effects of decomposing rice straw on growth and nitrogen fixation by Rhizobium journal of chemical ecology 7: 333-344

_________. 1984. Allelopathy (second edition). Academic Press, Orlando. p. 29-30.

ROMEO, J.T. 2000. Raising the beam: moving beyond phytotoxicity. Journal of Chemical Ecology 26:2011-2014.

ROSS, M.A. and C.A. LEMBI. 1999 Applied weed science. 2nd edn. Prentice-Hall. Upper Saddle River, New Jersey. 452p.

SAJJAN, A.S. and B.D. BIRADAR. 1998. Allelopathic effect of Cassia sericea on seed and seedling parameters in rabi sorghum. World Weeds 5: 81-83.

SANDRAS, V.O. and N. TRAPANI. 1999. Leaf expansion and phonologic development: key determinants of sunflower plasticity, growth and yield. In: SMITH, D.L. and C. HAMEL (eds), Physiological control of growth and yield in filed crops. Springer-Verlag, Berlin. pp. 205-232.

SCHMIDT, S.K. 1999. Microbial competition limits the toxicity of allelochemicals in natural soils. In Abstracts. Allelopathy Journal 7(1).pp 164.

SCHMIDIT, E.L. 1982. Nitrification in the soils. In Agronomy Monograph. 22p.

SCHON, M.K. and F.A. EINHELLIG. 1982. Allelopathic effects of cultivated sunflower on grain sorghum. Botanical Gazette. 143: 505-510.

SPRING, O. and A. HAGER. 1982. Inhibition of elongation growth by two sesquiterpene lactones isolated from Helianthus annuus. Peredovick. Pergamon. Phytochemistry, 21 : 2551-2553.

___________, K. ALBERT and A. HAGER. 1983. Three biologically active heliangolides from Helianthus annuus. Peredovick. Pergamon. Phytochemistry, 21 : 2551-2553.

SPOLLEN, W. G. and R.E. SHARP. 1991. Spatial distribution of turgor and root growth at low water potentials. Plant Physiology 96: 438-443.

STEINSIEK, J.W., L.R. OLIVER and F.C. COLLINS. 1982. Allelopathic potential of wheat straw on selected weed species. Weed Science. 30: 495-497.

STERLING, T.M., R.L. HOUTZ and A.R. PUTNAM. 1987. Phytotoxic exudates from velvetleaf (Abutilon theophrasti) glandular trichomes. American Journal of Botany 74: 543-550.

TAJA, H. and P.V.D. ZAAG. 1986. Mulching and residue incorporation effects on chemical and physical properties of an isohyperthermis typic agrius. Toll paper. 27p.

26

TIWARI, J. P., S.P. KURCHANIA, C.S. BHALLA and N.R. PARADKAR. 1998. Studies on allelopathic effects of Cassia tora on Parthenium hysterophorus. In Abstracts. Allelopathy Journal 6(2).pp.292.

TONGMA, S., K. KOBAYASHI and K. USUI. 1997. Effect of water extracts from Mexican sunflower [Tithonia diversifolia (Hemsl.) A. Gray] on germination and growth of tested plants. Journal of Weed Science and Technology 42: 373-378.

TSAO, R. and Q. YU. 2000. Nematicidal activity of monoterpenoid compounds against economically important nematodes in agriculture. J. Essent. Oil Res. 12, 350-354.

TUNG. P., ASHIMA and R.K. KOHLI. 1996. Alleopathic. Impact of sunflower (Helianthus annus L.)on Phaseolus aureus Roxb. In : R.K. Kohli, N. Jerath, and D. Batish (eds). Some facets of biodiversity. Researchco Publications, New Delhi, India. pp.219-227.

VISALAKSHI, M. and K.K.V. SARMA. 1998. Allelopathic potential of five weedy species of Cassia on nodulation and dry matter production of Arachis hypogaea L. In Abstracts. Allelopathy Journal. 6(2).pp 289.

WARDLE, D. A., K.J. NICHOLSON and M. AHMED. 1992. Comparison of osmotic and allelopathy effects of grass leaf extracts on grass seed germination and radicle elongation. Plant and soil 140: 315-319.

_____________, M.C. NILSON, C. GALLET and O. ZACKRISSON. 1998. An ecosystem level perspective of allelopathy. In Abstracts. Allelopathy Journal. 6(2).pp 278.

WATANABE, K., N. OHNO, H. YOSHIOKA, J. GERSHENZON and TOM J. MABRY. 1982. Sesquiterpene lactones and diterpenoids from Helianthus argophyllus. Peredovick. Pergamon. Phytochemistry, 21 : 709-713.

WILSON, R.E. and E.L. RICE. 1968. Allelopathy as expressed by Helianthus annus and its role in old-field succession. Bulletin of the Torrey Botanical Club. 95: 432-448.

WORSHAM, A.D. 1989. Strategies capitalizing on allelopathy. In phytochemical ecology: allelochemicals, mycotoxins, and insect pheromones and allomones; Chou, C.H., Waller, G.R. Eds. Institute of Botany, Academia Sinica Monograph 9, Taipei, Taiwan. pp 275-291.

ZEEVAART, J.A.D. 1977. Sites of abscisic acid synthesis and metabolism in Ricinus communis L. Plant Physiol. 59: 788-791.

ZUBILLAGA, M.M., J.P. ARISTI and R.S. LAVADO. 2002. Effect of phosphorus and nitrogen fertilization on sunflower (Helianthus annus L.). J. Agronomy and Crop Science 188, 267-274.

ZWAIN, K.H. 1999. Allelopathic effects of wheat (Triticum aestivum L.) on nitrogen cycle. In Abstracts. Allelopathy Journal 6(1) .pp. 100.