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Industrial Crops and Products 31 (2010) 289–293

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Industrial Crops and Products

journa l homepage: www.e lsev ier .com/ locate / indcrop

owpea (Vigna unguiculata L. Walp.) as a green manure to improve theroductivity of a menthol mint (Mentha arvensis L.) intercropping system

an Singh ∗, A. Singh, S. Singh, R.S. Tripathi, A.K. Singh, D.D. Patraentral Institute of Medicinal and Aromatic Plants (CIMAP), PO CIMAP, Lucknow 226015, India

r t i c l e i n f o

rticle history:eceived 24 March 2009eceived in revised form 4 November 2009ccepted 6 November 2009

eywords:entha arvensis

igna unguiculata

a b s t r a c t

A field experiment was conducted at Central Institute of Medicinal and aromatic Plants (CIMAP), Lucknow,India in a sandy loam soil (entisol) during 2004 and 2005. Cowpea (Vigna unguiculata L. Walp.) wasintercropped with transplanted menthol mint (Mentha arvensis L.) for green manuring (GM) and forfodder plus green manuring (F + GM) with four levels of urea N (0, 30, 60, 90 kg N ha−1). In GM, cowpeawas incorporated in the soil 30 days after sowing (DAS), while in F + GM 50% (alternate) cow pea plantswere used for fodder at 30 DAS and 50% were incorporated in soil at 35 DAS. No significant differenceswere found between GM and F + GM with respect to herb and oil yield of menthol mint and succeedingpalmarosa crop and nitrogen economy. Fresh biomass yield of menthol mint increased by 23.4% andessential oil yield by 25.2% by cowpea green manure (mean of GM and F + GM) as compared to without GM

ntercropping

reen manureymbopopogon martiniissential oil yield

across all N levels. The contribution of green manure, as a nitrogen source, was equivalent to 30 kg N ha−1

when no fertilizer nitrogen was applied in menthol mint. The residual effect of cowpea GM was studied ina succeeding crop of fast growing essential oil yielding palmarosa (Cymbopopogon martinii (Roxb.)Wats.var motia Burk.) over two harvests (July and December). Averaged across N levels green manure resultedin an increase of 18.5% in the fresh biomass and 17.7% in essential oil yield of palmarosa over no green

manuring.

. Introduction

During the last decade there has been consistent decline in therices of menthol mint oil. Therefore, it is critical to minimize theroduction inputs to offset the decrease in value. Declining organicarbon content in Indian soil is of greater cause of concern for futuretability in food production. Yadav (1998) concluded that intensivend continuous cereal cropping of paddy and wheat with fertilizerutrient has caused sharp decline in soil organic carbon status. This

s a major cause of concern in many countries in the world wishingo increase or sustain the present productivity level.

Menthol mint is an important cash crop in India. It has becomeost popular among small holders. In India, mint is cultivated

n approximately 1,60,000 ha of land with annual production of6,000 t of oil (Singh and Khanuja, 2007). Today, India is the majorlobal producer and supplier of mint oil and its derivatives in theorld. Mint has a high nutrient demand. Singh (1994) calculated

he N, P and K removal to the extent of 150, 25 and 100 kg ha−1,espectively. Application of 160 kg N ha−1 for delayed transplantedenthol mint was recommended by Ram and Kumar (1998). Sim-

lar 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 2003@yahoo.co.in (M. Singh).

926-6690/$ – see front matter © 2009 Elsevier B.V. All rights reserved.oi:10.1016/j.indcrop.2009.11.004

© 2009 Elsevier B.V. All rights reserved.

al. (2000) who worked on fertilizer requirement of menthol mint onthe basis of soil-test-crop response and under integrated nutrientmanagement 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 smalland most farm operations are performed by family labour. Mixedcropping involving legumes and non-legumes has been advocatedby several workers (Willey, 1979; Singh et al., 1989). Among oth-ers, the potential benefits of intercropping includes: (i) controlof soil erosion, (ii) insurance against crop failure, (iii) efficientutilization 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 observedincrease in soil nitrogen available to the non-legume either throughroot exudates or through ploughing off and decay of nodules

(Saito, 1981; Patra et al., 1989). Legume intercropping has thepotential to bring considerable economy in fertilizer nitrogenapplication. Kamprath et al. (1958) found that use of hairy vetch(Vicia villosa Roth.) as winter legume cover crop on Norfold soilsin North Carolina increased maize yields from 26 to 57 t ha−1,

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n increase comparable to that produced by the application of4–106 kg ha−1of nitrogen. Pandey and Pendleton (1986) observedhat soybean intercropping in maize could provide nitrogen equalo 28 kg N ha−1.

Intercropping of ‘dhaincha’ (Sesbania aculeata L.) for greenanure simultaneously with cane planting and incorporation in

oil after four weeks improved the cane production by 9.3% in therst ratoon and 6% in the second ratoon (Yadav and Dey, 2000). Innother study Yadav (2004) recorded significant increase in yieldf rice by intercropping of ‘dhaincha’ (S. aculeata) for green manure.ew studies have reported on legume intercropping in essential oilearing crops for additional bonus yield and return (Singh et al.,998; Prakasa Rao et al., 1986) and not for nitrogen economy.

The objective of the present study was to evaluate the use ofowpea (Vigna unguiculata L. Walp.) as a green manure in a mentholint (Mentha arvensis L.) intercropping system for improving the

roductivity and N economy in the soil–plant system.

. Materials and methods

A field experiment was conducted during 2004 and 2005 at theesearch farm of Central Institute of Medicinal and Aromatic Plants,ucknow (located at 26.5◦N, 80.5◦E and at 120 m above mean seaevel) in a sandy loam soil (entisol) being slightly alkaline in reactionpH 8.1) and having 0.3% organic carbon, 140 kg ha−1 available N,3.5 kg ha−1 available P and 160 kg ha−1 exchangeable K content inop 15 cm depth.

The experimental site is classified as semi-arid sub-tropical zoneith severe hot summer and fairly cool winters. In this region mon-

oon normally sets from last week of June and continues till endf September with an average annual rainfall of 700 mm. About0% of the monsoon rains are received in July and August. Winterlso experience some rains due to cyclonic disturbances in Arabicea. Mean maximum temperature fluctuated from 26.1 to 42.5 ◦C;hereas mean minimum temperature varied from 7.8 to 29.5 ◦C.

he temperature was lowest during mid December to end of Jan-ary and an increasing trend in mean temperature was noticedrom first week of February and reached to highest in mid Maynd it declines only after the onset of rains.

Twelve treatment combinations comprising three cropping sys-em, i.e. sole menthol mint, cowpea as a green manure with

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

evels of N (0, 30, 60, 90 kg N ha−1) through urea were tested in aandomized block design with three replications. The plot size was.6 m × 5 m.

Forty days old menthol mint (M. arvensis L.) cv. ‘Kosi’ nurseryaised plantlets were transplanted in to 60 cm wide rows at 10 cm

able 1erb and essential oil yield of menthol mint and palmarosa, agronomic efficiency (AE) an

wo years).

Treatment Herb yield (t fresh matter ha−1) Essential oil yield (kg ha−1)

Menthol mint Palmarosa Menthol mint Palmarosa

Cropping systemWithout GM 14.16 12.70 125.6 44.8Cowpea GM 17.07 14.79 153.6 51.8Cowpea F + GM 17.87 15.32 160.8 53.7LSD (P = 0.05) 1.40 0.90 12.6 3.2

Nitrogen levels (kg ha−1)0 10.54 12.03 94.6 42.130 14.67 13.57 132.0 47.460 18.0 15.63 162.0 54.890 22.24 15.85 200.0 56.0LSD (P = 0.05) 1.61 1.05 14.45 3.65

M, green manure; F, fodder; LSD, least significant difference; P = 0.05, at 5% probability;

Products 31 (2010) 289–293

plant to plant spacing in flooded plots in the fourth week of Marchin both years. A uniform dose of 60 kg P2O5 and 60 kg K2O ha−1

was applied as basal fertilizer before planting of mint and mixedin the soil. Total N was applied as per treatment in three equalsplits; before planting and 35 and 65 days after planting. Cowpeadid not receive any additional fertilizers. Cowpea cv. ‘Russian giant’was sown in between two rows of menthol mint at 15 kg ha−1. Theexperiment was conducted under irrigated conditions. Ten sur-face irrigations each of 50 mm depth were applied in mint at aninterval of 8–10 days by check basin method and two irrigationswere applied in palmarosa in mid October and mid November.Cowpea for green manure (GM) was incorporated in the soil 30days after sowing (DAS), whereas in cowpea fodder + green manure(F + GM) treatment alternate plants were cut for fodder 30 daysafter sowing and the remainder were incorporated in the soil 35days after sowing. Menthol mint crop was harvested 100 days aftertransplanting. After the harvest of menthol mint, plots were hoedby spade and 40-day-old seedlings of palmarosa (Cymbopopogonmartinii (Roxb.)Wats. var motia Burk.) were planted at 60 × 30 cmspacing on 15 July without application of any fertilizers. Palmarosawas harvested twice in mid October and end of December eachyear.

After harvest of menthol mint, soil samples were taken from top15 cm depth in each plot for analysis of organic carbon content fol-lowing Walkley and Black (1934) and available N following AlkalinePermanganate 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 collectedjust before harvesting from each plot and was hydro distilled ina Clevenger hydrodistillation apparatus. To obtain oil yield, freshherb yield was multiplied by oil content and by 0.9 (approxi-mate specific gravity of oil). Plant samples of menthol mint andpalmarosa were collected at harvest and of cowpea before incor-poration in soil for the estimation of dry biomass and N, P, K content,uptake and addition by respective crops. Plants were cut close tothe ground level from 2 m row length, these were first sun dried andthen oven dried at 70 ◦C for 48 h. Plant samples were wet digested indi-acid mixture (3HNO3:1HCl) for determination of P and K. Phos-phorus was determined by the Vanadomolybdo-phosphoric acidyellow colour method and neutral normal NH4OAc extractable K byflame photometer. N was determined by modified micro Kjeldahlmethod (Jackson, 1973).

N use efficiency was measured by calculating agronomic effi-ciency and N removal as follows.

Agronomic efficiency (kg oil kg−1 applied N) = [Essential oil yield(kg ha−1) in fertilized plot − Essential oil yield (kg ha−1) in control(N0) plot]/Fertilizer N (kg ha−1) applied.

d nitrogen removal as influenced by cropping system and nitrogen levels (mean of

AE (kg oil kg−1 applied N) Nitrogen removal (kg ha−1)

Menthol mint Palmarosa Menthol mint Palmarosa Total

0.95 0.17 47.7 36.4 84.11.23 0.18 59.8 43.0 102.81.26 0.19 61.6 44.6 106.20.12 NS 5.5 2.6 7.6

– – 35.7 34.2 69.91.15 0.18 50.1 39.2 89.31.12 0.21 61.5 45.5 107.01.17 0.15 76.9 46.1 123.0NS 0.02 6.3 3.0 8.8

NS, non significant.

M. Singh et al. / Industrial Crops and Products 31 (2010) 289–293 291

Table 2Amount of green biomass and N, P and K (kg ha−1) 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 GMN0 0 4500 20.4 4.0 12.5N30 0 4810 21.7 4.3 13.5N60 0 6200 27.9 5.6 16.0N90 0 6850 30.8. 6.1 18.3

Cowpea F + GMN0 1656 4450 20.0 4.0 12.0N30 2240 5000 22.5 4.5 14.0N60 3110 6389 28.8 5.7 17.0N90 3420 6680 30.5 6.0 18.0LSD (P = 0.05) 135.9 256.7 1.51 0.36 1.21

N, nitrogen.

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a 15 cm soil depth.b Contained 15% dry matter.

N removal (kg ha−1) = Dry matter yield (kg ha−1) × N content (%)n dry matter/100.

. Results and discussion

.1. Herb and oil yield of menthol mint and biomass yield ofowpea

No significant differences were found between the treatmentsM and F + GM with respect to herb and oil yield of mentholint and agronomic efficiency. Incorporation of cowpea greenanure significantly increased the fresh herb yield of mentholint by an average (mean of GM and F + GM) of 23.4% and oil

ield by 25.2% over the control without GM (Table 1). Averagedcross N levels, menthol mint yielded 1.23 and 1.26 kg of essentialil kg−1 applied N with cowpea GM and F + GM, respectively and.95 kg oil kg−1 applied N without GM (Table 1). Menthol mint andowpea responded significantly up to 90 kg N ha−1 as the highest Nevel 90 kg ha−1 was much lower than the 160 kg N ha−1 normallyecommended for menthol mint (Ram and Kumar, 1998). The con-ribution of green manure, as a nitrogen source, was equivalent

o 30 kg N ha−1 when no fertilizer nitrogen was applied (Fig. 1).andey and Pendleton (1986) also reported 28 kg N ha−1 contri-ution of soyabean green manure incorporated at 42 days afterowing in maize when no nitrogen was applied. In a similar study

ig. 1. Effect of nitrogen levels with and without cowpea green manure on mentholint yield.

using soil and fertilizer labeling technique with 15N on estima-tion of dinitrogen fixation by cowpea and concurrent transfer offix N to maize, Patra et al. (1986) reported a nitrogen benefit ofabout 30 kg ha−1 to the companion maize in maize cowpea inter-cropping. A significant increase in biomass yield of legume greenmanure crops with the application of N up to 60 kg ha−1 was alsorecorded by Jeranyama et al. (2000) and Yadav (2004). The higherbiomass of mint and intercrop cowpea is understandable in viewof the fact that in the early stages, growth of menthol mint beingextremely low, cowpea could be able to utilize full advantages ofavailable growth resources whereas in the subsequent stage mintdid not face any competition with the companion crop which wasincorporated in soil at 30–35 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 ofdaily net photosynthesis.

Although the contribution of cowpea green manure was smallit may be significant for small farmers whose cash input is lim-ited. When cowpea was incorporated as green manure at 30 and35 days after sowing, it produced 4450 (N0 GM) to 6850 (N90,GM) kg green biomass which contained 20–30.8 kg N, 4.0–6.1 kg Pand 12.0–18.3 kg K ha−1 (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 30DAS as it was the grand growth period of cowpea. There was nointerplant competition, soil moisture was sufficient and weatherconditions were suitable. Maximum temperature 35–40 ◦C, mini-mum temperature 20–25 ◦C and bright sunny days induced veryfast growth of cowpea as all the cultivars of cowpea are consid-ered as warm season, adapted to hot and drought conditions andrespond well to optimum soil moisture. Aikins and Afuakwa (2008)also reported about 50% increase in plant height, 25% increasein stem girth and 100% increase in number of leaves per plantin cowpea within a period of one week (between four and fiveweeks after emergence) at Kumasi, Ghana. Besides shoot biomass,un-quantified amounts of decomposing roots and nodules mighthave contributed nitrogen to the menthol mint (Patra et al., 1989).Cowpea F + GM also yielded 1656–3420 kg ha−1 green fodder as abonus 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); rice–wheat system by Yadavet al. (2000) and Yadav (2004), in maize by Pandey and Pendleton(1986) and Jeranyama et al. (2000) and in tomato–maize systemby Thonnissen et al. (2000). In intercropping system involvingwheat and alfalfa, protein yield of wheat crop was significantly

292 M. Singh et al. / Industrial Crops and

Table 3Soil organic carbon content and available nitrogen after harvest of menthol mint asinfluenced by cowpea green manure under different N levels (mean of two years)a.

Treatment Organic carboncontent (%)

Available nitrogen (kg ha−1)

Cropping systemWithout GM 0.326 161.2Cowpea GM 0.336 173.8Cowpea F + GM 0.336 175.6LSD (P = 0.05) NS 9.3

Nitrogen levels (kg ha−1)N0 0.328 162.9N30 0.331 169.7N60 0.334 173.6

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N90 0.335 174.6LSD (P = 0.05) NS 10.8

a In top 15 cm soil; N, nitrogen; GM, green manure; F, fodder; NS, non significant.

ncreased over wheat grown as sole crop (Magid Abdel et al.1991).

.2. Residual effect

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

eeding palmarosa crop (Table 1). No significant differences wereound between the treatments GM and F + GM with respect toerb and oil yield of palmarosa. Intercropping of cowpea for GMesulted in 18.5% increases in fresh biomass and 17.7% increase inil yield of palmarosa over that without GM. It was due to enrich-ng of soil by an average (mean of G and F + G) 13.4 kg N ha−1,.e. 8.4% increase in available N over no green manure (Table 3).hough incorporation of cowpea GM in mint did not increase therganic carbon content in the soil significantly but it enhancedhe content by 3.1% over no GM. There was no significant differ-nce in agronomic efficiency (kg oil kg−1 applied N) in palmarosaue to GM when averaged over N rates. However, palmarosaielded 0.18 and 0.19 kg oil kg−1 applied N with GM and F + GM,espectively and 0.17 kg oil kg−1 applied N without GM (Table 1).honnissen et al. (2000) also recorded significant residual effectf green manure and fertilizer N applied to tomato on dry mat-er accumulation and N removal by succeeding maize. The residualffect of soybean GM applied to tomato on the following maizeas similar to that of 120 kg N ha−1. Yadav (2004) also reported

ignificant residual effects of S. aculeata green manure applied toice on grain yield of succeeding wheat, agronomic efficiency andecovery efficiency of N particularly when low N was applied toheat. Similar residual effect of cowpea intercropping and nitro-

en in maize was also reported in succeeding wheat by Patra etl. (1989).

.3. Nitrogen removal

Removal of N by menthol mint, palmarosa and total signif-cantly increased with cowpea GM and N levels (Table 1). Noignificant differences were found between the treatments GMnd F + GM. Incorporation of cowpea for GM on an average (meanf GM and F + GM) increased the N removal by 27.3%, 20.5%nd 24.3%, through menthol mint, palmarosa and total (mentholint + palmarosa), respectively as compared to that without greenanure.

. Conclusions

Based on our results, it is apparent that intercropping of fastrowing fodder variety of cowpea both for fodder and green manure

Products 31 (2010) 289–293

in menthol mint for 35 days improved the efficiency of nitrogenfertilizer and economized about 30 kg N ha−1, improved the soilfertility and yield of succeeding palmarosa crop. It also produced1656–3420 kg ha−1 green fodder as a bonus which is of significantvalue during summer in mint growing areas. This practice is morebeneficial 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 ofMedicinal and Aromatic plants, Lucknow for providing facilities.

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