cowpea (vigna unguiculata l. walp.) as a green manure to improve the

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Industrial Crops and Products 31 (2010) 289293

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Industrial Crops and Products

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Cowpea (Vigna unguiculataL. Walp.) as a green manure to improve the

productivity of a menthol mint (Mentha arvensisL.) intercropping system

Man Singh, A. Singh, S. Singh, R.S. Tripathi, A.K. Singh, D.D. Patra

Central Institute of Medicinal and Aromatic Plants (CIMAP), PO CIMAP, Lucknow 226015, India

a r t i c l e i n f o

Article history:

Received 24 March 2009

Received in revised form 4 November 2009Accepted 6 November 2009

Keywords:

Mentha arvensis

Vigna unguiculata

Intercropping

Green manure

Cymbopopogon martinii

Essential oil yield

a b s t r a c t

A fieldexperiment wasconductedat Central Instituteof Medicinaland aromaticPlants(CIMAP),Lucknow,

India in a sandy loam soil (entisol) during 2004 and 2005. Cowpea ( Vigna unguiculata L. Walp.) was

intercropped with transplanted menthol mint (Mentha arvensis L.) for green manuring (GM) and for

fodder plus green manuring (F + GM) with four levels of urea N (0, 30, 60, 90 kg N ha1). In GM, cowpea

was incorporated in the soil 30 days after sowing (DAS), while in F+ GM 50% (alternate) cow pea plants

were used for fodder at 30 DAS and 50% were incorporated in soil at 35 DAS. No significant differences

were found between GM and F+ GM with respect to herb and oil yield of menthol mint and succeeding

palmarosa crop and nitrogen economy. Fresh biomass yield of menthol mint increased by 23.4% and

essentialoil yieldby 25.2%by cowpeagreen manure(mean ofGM andF + GM)as comparedto without GM

acrossall N levels. Thecontribution of green manure, as a nitrogen source, wasequivalentto 30kg N ha1

when no fertilizer nitrogenwas applied in menthol mint. Theresidual effectof cowpeaGM was studied in

a succeeding crop of fast growing essential oil yielding palmarosa (Cymbopopogon martinii(Roxb.)Wats.

varmotia Burk.) over two harvests (July andDecember). Averaged acrossN levelsgreen manure resulted

in an increase of 18.5% in the fresh biomass and 17.7% in essential oil yield of palmarosa over no green

manuring.

2009 Elsevier B.V. All rights reserved.

1. Introduction

During the last decade there has been consistent decline in the

prices of menthol mint oil. Therefore, it is critical to minimize the

production inputs to offset the decrease in value. Declining organic

carboncontentin Indiansoilis of greater cause of concern forfuture

stability in food production. Yadav (1998) concluded that intensive

and continuous cereal cropping of paddy and wheat with fertilizer

nutrient has caused sharp decline in soil organic carbonstatus. This

is a major cause of concern in many countries in the world wishing

to increase or sustain the present productivity level.

Menthol mint is an important cash crop in India. It has become

most popular among small holders. In India, mint is cultivated

on approximately 1,60,000 ha of land with annual production of16,000 t of oil (Singh and Khanuja, 2007).Today, India is the major

global producer and supplier of mint oil and its derivatives in the

world. Mint has a high nutrient demand.Singh (1994)calculated

the N, P and K removal to the extent of 150, 25 and 100kg ha1,

respectively. Application of 160kg N ha1 for delayed transplanted

menthol mint was recommended byRam and Kumar (1998).Sim-

ilar observations were also made by Patra et al. (1998) and Patra et

Corresponding author. Tel.: +91 9453020644; fax: +91 522 2342666.

E-mail address:mansingh [email protected](M. Singh).

al. (2000) who workedon fertilizer requirementof menthol mint on

the basis of soil-test-crop response and under integrated nutrient

management system.

Intercropping, the practice of growing two or more crop simul-

taneously in the same area in a year (Andrews and Kassam, 1976)

has continued to be popular in the developing world, more gen-

uinely where the level of mechanization is low, holdings are small

and most farm operations are performed by family labour. Mixed

cropping involving legumes and non-legumes has been advocated

by several workers (Willey, 1979; Singh et al., 1989).Among oth-

ers, the potential benefits of intercropping includes: (i) control

of soil erosion, (ii) insurance against crop failure, (iii) efficient

utilization of resources by plants with different growth periods,

height, rooting systems, and nutrient requirements, and (iv) trans-fer of nitrogen fixed by legumes to the companion grass species

(Patra et al., 1986; Patra and Subbaih, 1987; Itula and Aguyoh,

1998).

However, the main advantage is considered to the observed

increase in soilnitrogen availableto the non-legumeeither through

root exudates or through ploughing off and decay of nodules

(Saito, 1981; Patra et al., 1989). Legume intercropping has the

potential to bring considerable economy in fertilizer nitrogen

application.Kamprath et al. (1958)found that use of hairy vetch

(Vicia villosa Roth.) as winter legume cover crop on Norfold soils

in North Carolina increased maize yields from 26 to 57 t ha1,

0926-6690/$ see front matter 2009 Elsevier B.V. All rights reserved.

doi:10.1016/j.indcrop.2009.11.004
http://www.sciencedirect.com/science/journal/09266690http://www.elsevier.com/locate/indcropmailto:[email protected]://localhost/var/www/apps/conversion/tmp/scratch_1/dx.doi.org/10.1016/j.indcrop.2009.11.004http://localhost/var/www/apps/conversion/tmp/scratch_1/dx.doi.org/10.1016/j.indcrop.2009.11.004mailto:[email protected]://www.elsevier.com/locate/indcrophttp://www.sciencedirect.com/science/journal/09266690


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290 M. Singh et al. / Industrial Crops and Products31 (2010) 289293

an increase comparable to that produced by the application of

84106kg ha1of nitrogen. Pandey and Pendleton (1986) observed

that soybean intercropping in maize could provide nitrogen equal

to 28 kgN ha1.

Intercropping of dhaincha (Sesbania aculeata L.) for green

manure simultaneously with cane planting and incorporation in

soil after four weeks improved the cane production by 9.3% in the

first ratoon and 6% in the second ratoon (Yadav and Dey, 2000).In

another studyYadav (2004)recorded significant increase in yield

of rice byintercropping of dhaincha (S. aculeata) forgreenmanure.

Few studies have reported on legume intercropping in essential oil

bearing crops for additional bonus yield and return (Singh et al.,

1998; Prakasa Rao et al., 1986)and not for nitrogen economy.

The objective of the present study was to evaluate the use of

cowpea(Vigna unguiculataL. Walp.)as a green manurein a menthol

mint (Mentha arvensisL.) intercropping system for improving the

productivity and N economy in the soilplant system.

2. Materials and methods

A field experiment was conducted during 2004 and 2005 at the

research farm of Central Instituteof Medicinaland AromaticPlants,

Lucknow (located at 26.5N, 80.5E and at 120 m above mean sea

level)inasandyloamsoil(entisol)beingslightlyalkalineinreaction

(pH 8.1) and having 0.3% organic carbon, 140 kg ha1 available N,

13.5kgha1 available P and 160 kgha1 exchangeable K content in

top 15 cm depth.

The experimental siteis classifiedas semi-aridsub-tropicalzone

with severehot summerand fairlycool winters. In this regionmon-

soon normally sets from last week of June and continues till end

of September with an average annual rainfall of 700mm. About

80% of the monsoon rains are received in July and August. Winter

also experience some rains due to cyclonic disturbances in Arabic

sea. Mean maximum temperature fluctuated from 26.1 to 42.5 C;

whereas mean minimum temperature varied from 7.8 to 29.5 C.

The temperature was lowest during mid December to end of Jan-

uary and an increasing trend in mean temperature was noticed

from first week of February and reached to highest in mid May

and it declines only after the onset of rains.

Twelve treatmentcombinations comprising three cropping sys-

tem, i.e. sole menthol mint, cowpea as a green manure with

menthol mint, cowpea as both fodder and green manure and four

levels of N (0, 30, 60, 90kgNha1) through urea were tested in a

randomized block design with three replications. The plot size was

3.6m5 m.

Forty days old menthol mint (M. arvensis L.) cv. Kosi nursery

raised plantlets were transplanted in to 60 cm wide rows at 10 cm

plant to plant spacing in flooded plots in the fourth week of March

in both years. A uniform dose of 60kg P 2O5 and 60kgK2O ha1

was applied as basal fertilizer before planting of mint and mixed

in the soil. Total N was applied as per treatment in three equal

splits; before planting and 35 and 65 days after planting. Cowpea

didnot receive anyadditional fertilizers. Cowpeacv. Russian giant

was sown in between two rows of menthol mint at15 kgha1. The

experiment was conducted under irrigated conditions. Ten sur-

face irrigations each of 50 mm depth were applied in mint at an

interval of 810 days by check basin method and two irrigations

were applied in palmarosa in mid October and mid November.

Cowpea for green manure (GM) was incorporated in the soil 30

days after sowing (DAS), whereas in cowpeafodder + green manure

(F + GM) treatment alternate plants were cut for fodder 30 days

after sowing and the remainder were incorporated in the soil 35

days after sowing. Menthol mint crop was harvested100 days after

transplanting. After the harvest of menthol mint, plots were hoed

by spade and 40-day-old seedlings of palmarosa (Cymbopopogon

martinii(Roxb.)Wats. var motia Burk.) were planted at 60 30cm

spacing on 15 July without application of any fertilizers. Palmarosa

was harvested twice in mid October and end of December each

year.

After harvest of menthol mint, soil samples were taken from top

15cm depth in each plot for analysis of organic carbon content fol-lowing Walkley and Black(1934)and availableN following Alkaline

Permanganate Method (Subbaih and Asija, 1956).

For the estimation of essential oil content in fresh herb of men-

thol mint and palmarosa, 200 g green plant biomass was collected

just before harvesting from each plot and was hydro distilled in

a Clevenger hydrodistillation apparatus. To obtain oil yield, fresh

herb yield was multiplied by oil content and by 0.9 (approxi-

mate specific gravity of oil). Plant samples of menthol mint and

palmarosa were collected at harvest and of cowpea before incor-

porationin soil forthe estimation of drybiomassand N,P, K content,

uptake and addition by respective crops. Plants were cut close to

theground level from 2 m rowlength, these were first sundriedand

then oven driedat 70Cfor48h.Plantsampleswerewetdigestedin

di-acid mixture (3HNO3:1HCl) for determination of P and K. Phos-phorus was determined by the Vanadomolybdo-phosphoric acid

yellowcolour methodand neutral normalNH4OAcextractableK by

flame photometer. N was determined by modified micro Kjeldahl

method (Jackson, 1973).

N use efficiency was measured by calculating agronomic effi-

ciency and N removal as follows.

Agronomicefficiency(kg oilkg1 applied N)= [Essential oilyield

(kgha1) in fertilized plotEssential oil yield (kg ha1) in control

(N0) plot]/Fertilizer N (kg ha1) applied.

Table 1

Herb and essential oil yield of menthol mint and palmarosa, agronomic efficiency (AE) and nitrogen removal as influenced by cropping system and nitrogen levels (mean of

two years).

Treatment Herb yield (tfresh matterha1) Essential oil yield (kgha1) AE (kg oil kg1 appliedN) Nitrogen removal (kgha1)

Me ntho l mint Palmaro sa Me ntho l mint P almar os a Men th ol mint Palmar osa Menthol mint Palmaro sa To tal

Cropping system

Without GM 14.16 12.70 125.6 44.8 0.95 0.17 47.7 36.4 84.1

Cowpea GM 17.07 14.79 153.6 51.8 1.23 0.18 59.8 43.0 102.8

Cowpea F + GM 17.87 15.32 160.8 53.7 1.26 0.19 61.6 44.6 106.2

LSD (P= 0.05) 1.40 0.90 12.6 3.2 0.12 NS 5.5 2.6 7.6

Nitrogen levels (kg ha1)

0 10.54 12.03 94.6 42.1 35.7 34.2 69.9

30 14.67 13.57 132.0 47.4 1.15 0.18 50.1 39.2 89.3

60 18.0 15.63 162.0 54.8 1.12 0.21 61.5 45.5 107.0

90 22.24 15.85 200.0 56.0 1.17 0.15 76.9 46.1 123.0

LSD (P= 0.05) 1.61 1.05 14.45 3.65 NS 0.02 6.3 3.0 8.8

GM, green manure; F, fodder; LSD, least significant difference;P= 0.05, at 5% probability; NS, non significant.


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M. Singh et al. / Industrial Crops and Products 31 (2010) 289293 291

Table 2

Amount of green biomass and N, P and K (kg ha1) added by cowpea green manure under different nitrogen levels (mean of two years).

Cropping system Green biomass for fodder Amount addeda

Green biomass for GMb N P K

Cowpea GM

N0 0 4500 20.4 4.0 12.5

N30 0 4810 21.7 4.3 13.5

N60 0 6200 27.9 5.6 16.0

N90 0 6850 30.8. 6.1 18.3

Cowpea F + GM

N0 1656 4450 20.0 4.0 12.0

N30 2240 5000 22.5 4.5 14.0

N60 3110 6389 28.8 5.7 17.0

N90 3420 6680 30.5 6.0 18.0

LSD (P= 0.05) 135.9 256.7 1.51 0.36 1.21

N, nitrogen.a 15 cm soil depth.b Contained 15% dry matter.

N removal (kg ha1) = Dry matter yield (kg ha1)N content (%)

in dry matter/100.

3. Results and discussion

3.1. Herb and oil yield of menthol mint and biomass yield of

cowpea

No significant differences were found between the treatments

GM and F+GM with respect to herb and oil yield of menthol

mint and agronomic efficiency. Incorporation of cowpea green

manure significantly increased the fresh herb yield of menthol

mint by an average (mean of GM and F + GM) of 23.4% and oil

yield by 25.2% over the control without GM (Table 1). Averaged

across N levels, menthol mint yielded 1.23 and 1.26 kg of essential

oilkg1 applied N with cowpea GM and F + GM, respectively and

0.95kgoilkg1 applied N without GM (Table 1).Menthol mint and

cowpea responded significantly up to 90kg N ha1 as the highest N

level 90 kg ha1 was much lower than the 160 kg N ha1 normally

recommended for menthol mint (Ram and Kumar, 1998).The con-

tribution of green manure, as a nitrogen source, was equivalent

to 30kgNha1 when no fertilizer nitrogen was applied (Fig. 1).

Pandey and Pendleton (1986) also reported 28kgNha1 contri-

bution of soyabean green manure incorporated at 42 days after

sowing in maize when no nitrogen was applied. In a similar study

Fig. 1. Effect of nitrogenlevels withand without cowpea green manure on menthol

mint yield.

using soil and fertilizer labeling technique with 15N on estima-

tion of dinitrogen fixation by cowpea and concurrent transfer of

fix N to maize, Patra et al. (1986)reported a nitrogen benefit of

about 30kgha1 to the companion maize in maize cowpea inter-cropping. A significant increase in biomass yield of legume green

manure crops with the application of N up to 60 kg ha1 was also

recorded byJeranyama et al. (2000)andYadav (2004).The higher

biomass of mint and intercrop cowpea is understandable in view

of the fact that in the early stages, growth of menthol mint being

extremely low, cowpea could be able to utilize full advantages of

available growth resources whereas in the subsequent stage mint

did not face any competition with the companion crop which was

incorporated in soil at 3035 days after sowing. Trenbath (1979)

postulated that under non-limiting soil conditions, crops of differ-

ent heights, like wheat and alfalfa, have an advantage in terms of

daily net photosynthesis.

Although the contribution of cowpea green manure was small

it may be significant for small farmers whose cash input is lim-ited. When cowpea was incorporated as green manure at 30 and

35 days after sowing, it produced 4450 (N0 GM) to 6850 (N90,

GM) kg green biomass which contained 2030.8 kg N, 4.06.1kg P

and 12.018.3kg K ha1 (Table 2).In F + GM treatment 50% (alter-

nate) plants were cut at 30 DAS for fodder; the remaining 50%

plants were allowed to grow for five more days till 35 DAS accu-

mulated almost same amount of biomass as 100% plants at 30

DAS as it was the grand growth period of cowpea. There was no

interplant competition, soil moisture was sufficient and weather

conditions were suitable. Maximum temperature 3540 C, mini-

mum temperature 2025 C and bright sunny days induced very

fast growth of cowpea as all the cultivars of cowpea are consid-

ered as warm season, adapted to hot and drought conditions and

respond well to optimum soil moisture.Aikins and Afuakwa (2008)also reported about 50% increase in plant height, 25% increase

in stem girth and 100% increase in number of leaves per plant

in cowpea within a period of one week (between four and five

weeks after emergence) at Kumasi, Ghana. Besides shoot biomass,

un-quantified amounts of decomposing roots and nodules might

have contributed nitrogen to the menthol mint (Patra et al., 1989).

Cowpea F + GM also yielded 16563420 kg ha1 green fodder as a

bonus which is of significant value during summer in mint grow-

ing areas. The beneficial effect of green manuring has also been

reported in other crops (not mint); ricewheat system by Yadav

et al. (2000)andYadav (2004),in maize byPandey and Pendleton

(1986)andJeranyama et al. (2000) and in tomatomaize system

by Thonnissen et al. (2000). In intercropping system involving

wheat and alfalfa, protein yield of wheat crop was significantly


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292 M. Singh et al. / Industrial Crops and Products31 (2010) 289293

Table 3

Soil organic carbon content and available nitrogen after harvest of menthol mint as

influenced by cowpea green manure under different N levels (mean of two years)a.

Treatment Organic carbon

content (%)

Available nitrogen (kg ha1)

Cropping system

Without GM 0.326 161.2

Cowpea GM 0.336 173.8

Cowpea F + GM 0.336 175.6

LSD (P= 0.05) NS 9.3Nitrogen levels (kg ha1)

N0 0.328 162.9

N30 0.331 169.7

N60 0.334 173.6

N90 0.335 174.6

LSD (P= 0.05) NS 10.8

a In top15 cm soil;N, nitrogen;GM, green manure; F, fodder; NS, nonsignificant.

increased over wheat grown as sole crop (Magid Abdel et al.

(1991).

3.2. Residual effect

The residual effects of green manure and N doses applied tomenthol mint were significant on fresh herb and oil yield of suc-

ceeding palmarosa crop (Table 1).No significant differences were

found between the treatments GM and F + GM with respect to

herb and oil yield of palmarosa. Intercropping of cowpea for GM

resulted in 18.5% increases in fresh biomass and 17.7% increase in

oil yield of palmarosa over that without GM. It was due to enrich-

ing of soil by an average (mean of G and F+G) 13.4kgNha1,

i.e. 8.4% increase in available N over no green manure (Table 3).

Though incorporation of cowpea GM in mint did not increase the

organic carbon content in the soil significantly but it enhanced

the content by 3.1% over no GM. There was no significant differ-

ence in agronomic efficiency (kg oil kg1 applied N) in palmarosa

due to GM when averaged over N rates. However, palmarosa

yielded 0.18 and 0.19 kg oilkg

1

appliedN with GM and F+GM,respectively and 0.17kg oil kg1 applied N without GM (Table 1).

Thonnissen et al. (2000)also recorded significant residual effect

of green manure and fertilizer N applied to tomato on dry mat-

ter accumulation and N removal by succeeding maize. The residual

effect of soybean GM applied to tomato on the following maize

was similar to that of 120kgNha1. Yadav (2004)also reported

significant residual effects ofS. aculeata green manure applied to

rice on grain yield of succeeding wheat, agronomic efficiency and

recovery efficiency of N particularly when low N was applied to

wheat. Similar residual effect of cowpea intercropping and nitro-

gen in maize was also reported in succeeding wheat by Patra et

al. (1989).

3.3. Nitrogen removal

Removal of N by menthol mint, palmarosa and total signif-

icantly increased with cowpea GM and N levels (Table 1). No

significant differences were found between the treatments GM

and F + GM. Incorporation of cowpea for GM on an average (mean

of GM and F + GM) increased the N removal by 27.3%, 20.5%

and 24.3%, through menthol mint, palmarosa and total (menthol

mint + palmarosa), respectively as compared to that without green

manure.

4. Conclusions

Based on our results, it is apparent that intercropping of fast

growing fodder variety of cowpea bothfor fodder andgreen manure

in menthol mint for 35 days improved the efficiency of nitrogen

fertilizer and economized about 30 kg N ha1, improved the soil

fertility and yield of succeeding palmarosa crop. It also produced

16563420 kg ha1 green fodder as a bonus which is of significant

value during summer in mint growing areas. This practice is more

beneficial when palmarosa or any cereal crop is grown as succeed-

ing crop with limited fertilizer nitrogen.

Acknowledgement

The authors are thankful to the Director, Central Institute of

Medicinal and Aromatic plants, Lucknow for providing facilities.

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cowpea (vigna unguiculata l. walp.) as a green manure to improve the

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