Exploring Maize-Legume Intercropping Systems in Southwest Mexico

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Exploring Maize-Legume IntercroppingSystems in Southwest MexicoD. Flores-Sanchez a , A. Pastor b , E. A. Lantinga b , W. A. H. Rossingb & M. J. Kropff ca Colegio de Postgraduados, Montecillo , Edo , de Mexico , Mexicob Farming Systems Ecology Group, Wageningen University ,Wageningen , the Netherlandsc Crop and Weed Ecology Group, Wageningen University ,Wageningen , the NetherlandsAccepted author version posted online: 16 Jan 2013.Publishedonline: 22 Jul 2013.

To cite this article: D. Flores-Sanchez , A. Pastor , E. A. Lantinga , W. A. H. Rossing & M. J. Kropff(2013) Exploring Maize-Legume Intercropping Systems in Southwest Mexico, Agroecology andSustainable Food Systems, 37:7, 739-761, DOI: 10.1080/21683565.2013.763888

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Agroecology and Sustainable Food Systems, 37:739–761, 2013Copyright © Taylor & Francis Group, LLCISSN: 2168-3565 print/2168-3573 onlineDOI: 10.1080/21683565.2013.763888

Exploring Maize-Legume IntercroppingSystems in Southwest Mexico

D. FLORES-SANCHEZ,1 A. PASTOR,2 E. A. LANTINGA,2

W. A. H. ROSSING,2 and M. J. KROPFF3

1Colegio de Postgraduados, Montecillo, Edo de Mexico, Mexico2Farming Systems Ecology Group, Wageningen University, Wageningen, the Netherlands3Crop and Weed Ecology Group, Wageningen University, Wageningen, the Netherlands

Maize yields in continuous maize production systems ofsmallholders in the Costa Chica, a region in Southwest Mexico, arelow despite consistent inputs of fertilizers and herbicides. This studywas aimed at investigating the prospects of intercropping maize(Zea mays L.) and maize-roselle (Hibiscus sabdariffa L.) mixtureswith the legumes canavalia (Canavalia brasiliensis Mart. ex Benth)and mucuna (Mucuna pruriens var. utilis) for improving nutrientuptake and weed suppression. Farmer-managed experiments wereestablished in two communities in the region during 2006 and2007 using randomized split-plot designs. Maize monocrops andmaize-roselle intercrops grown with different sources of nutrientswere intercropped with both legume species, sown 4–6 weeks aftermaize. Neither the legumes decreased yields of maize nor roselle,whereas they caused a reduction of the weed biomass by 24–55%.Total aboveground biomass returned to the soil increased up to36% and total N, P, and K uptake was increased on average by52%, 24%, and 30%, respectively. Legumes acted not only as aN-fixing crop, but also as a “catch” crop, preventing N and Kleaching. With its prostrate growth habit and adaptation to poorsoil conditions, canavalia demonstrated agronomic advantages incomparison to mucuna.

KEYWORDS intercropping, maize yield, canavalia, mucuna,weed suppression

Address correspondence to D. Flores-Sanchez, Colegio de Postgraduados, Montecillo,Edo de Mexico, CP 56230, Mexico. E-mail: [email protected], [email protected]

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740 D. Flores-Sanchez et al.

INTRODUCTION

In Costa Chica, a subhumid tropical region in Southwest Mexico, smallholderfarming systems are characterized by continuous cultivation of maize (Zeamays L.) and roselle (Hibiscus sabdariffa L.) under rainfed conditions. Maizeis grown for self consumption, while roselle is a cash crop cultivated for itscalyces that are used to make a beverage. Subsidized N and P artificial fer-tilizers are the main source of nutrients. Cropping on slopes as steep as 50%makes fertilizers susceptible to runoff. Traditional practices to restore soil fer-tility such as fallow management have been nearly abandoned. According tofarmers’ perception, these cropping management changes have led to “tiredsoils,” an increase in weed pressure, and an overall reduction in crop yields.Manual control of weeds is not practiced anymore because it is time consum-ing, labor-intensive and, therefore, expensive. Herbicides (mainly Paraquat)are widely used at high doses, and they can have potential impact on humanand animal health (Jordan 1996).

Inclusion of legumes like mucuna or velvet bean (Mucuna pruriensvar. utilis), slender leaf rattlebox (Crotalaria ochroleuca G. Don), jackbean(Canavalia ensiformis L.), and Brazilian jackbean (Canavalia brasiliensisMart. ex Benth) in cropping systems has been shown to play an impor-tant role in N recycling within the systems, improving crop yields, reducinglabor for weed control, decreasing soil erosion, and improving soil physi-cal properties (Reddy et al. 1986; Becker and Johnson 1998; Tarawali et al.1999; Buckles et al. 2000; Ortiz-Ceballos and Fragoso 2004; Lawson et al.2007). However, benefits depended strongly on local biophysical conditionsand crop management as intercropping may cause interspecific competitionbetween the legumes and the main crops (Lawson et al. 2007). To tacklethe problem of site-specific competition with the main crop, it has been sug-gested to delay the legume sowing date by about 2–6 weeks to maintain maincrop yields (Akanvou et al. 2002; Eilittä et al. 2003). Mucuna has been inte-grated into maize systems in different regions of Mexico. In the Costa Chica,a leading farmer developed empirically a system that, however, was consid-ered unwieldy by other farmers due to the abundant growth of mucuna.

As part of a larger project aimed at learning about integrated nutri-ent management, the local farmer’s experience with intercropping mucunainspired researcher-guided, farmer-managed experiments with maize andmaize-roselle cropping systems. In the experiments, which ran during twoyears, the effects of intercropping with leguminous crops and differentorganic nutrient sources were investigated. The overall objective was toexplore more productive crop management systems by increasing nutrientuse efficiency and reducing inputs of herbicides. In a companion paperthe effects of alternative nutrient management are reported (Flores-Sanchez2013). In this article, we describe first-year effects of intercropping maize andmaize-roselle with mucuna and canavalia. Specific objectives were to deter-mine the effects of intercropped legumes on yields of maize and roselle and

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Maize-Legume Intercropping Systems 741

on weed biomass suppression of the cropping systems. Besides, the hypoth-esis was tested that inclusion of legumes in maize and maize-roselle systemscontribute to improved N cycling within the cropping systems.

MATERIALS AND METHODS

Experimental Sites

Five field experiments were conducted on farmers’ fields located in themunicipality of Tecoanapa (16◦48’N, 99◦09’W), Guerrero, Mexico, in two suc-cessive growing seasons (2006 and 2007). Annual rainfall in the experimentalarea was 1,926 mm in 2006 and 1,822 mm in 2007, mainly concentrated in theperiod between June and October. Mean annual temperature was 25oC, withlittle variation within the year. Two villages were devoted to the experimentalstudy. In 2006, a trial was conducted in the village Xalpatlahuac. In 2007, twoexperiments were located in Las Animas, and two in Xalpatlahuac (Table 1).Fields belonged to participant farmers, thus, the experimental sites variedsubstantially in terms of slope and soil fertility. The soils in the experimentalarea were loamy Eutric Regosols, which have a volcanic origin (SEMARNAT2009) and are defined by the Food and Agriculture Organization of theUnited Nations ([FAO] 2006) as weakly developed with a texture finer thansandy loam. In an earlier survey (Flores-Sanchez et al. 2011) maize was foundto be grown on fields with slopes between 5% and 55%. In the region, traitsof rill erosion are common and the general level of erosion is classified asmoderate (10–50 Mg ha−1 year−1) (SEMARNAT–UACH 2002).

Experimental Procedures

EXPERIMENT IN 2006

A trial was set up in a maize crop on one farm following a randomized blockdesign in a split-plot arrangement with three replications. The main plotsincluded three treatments: Mucuna pruriens var. utilis, Canavalia brasilien-sis Mart. ex Benth, and no legume. Mucuna is a vigorous annual species, witha climbing growth habit, and it produces abundant seed. It performs well insoils from moderate to high fertility and tolerates pH values between 5 and8, and can grow on sandy soils (Kass and Somarriba 1999; Peters et al. 2003).Canavalia brasiliensis is an underutilized perennial legume species with arelatively stable biomass production due to its tolerance for adverse environ-mental conditions, combined with its prostrate growth habit (Humbert et al.2008). The legumes were sown midway between the rows of maize in anadditive design. The subplots were fertilized with: 1) vermicompost, 2) goatmanure, 3) mineral NPK, and 4) unfertilized control (Table 1). Unfortunately,not enough manure and vermicompost was available to reach the nutrientsupply of the NPK treatment, therefore, nutrient input levels were divergent.

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TAB

LE1

Exp

erim

enta

lsi

tes,

croppin

gsy

stem

s,an

dtrea

tmen

tsev

aluat

edin

five

exper

imen

ts

Nutrie

ntin

puts

(kg

ha−

1)

Yea

rExp

.Code

Cro

ppin

gsy

stem

sM

ain

plo

tsSu

bplo

tsN

PK

2006

1∗M

-1m

uM

-1ca

M-1

nl

Mai

zeM

ucu

na

Can

aval

iaN

ole

gum

e

Ver

mic

om

post

(2.5

Mg

DM

ha−

1)

332

15G

oat

man

ure

(2.5

Mg

DM

ha−

1)

341

18N

PK

(56-

04-2

9)56

224

Unfe

rtili

zed

00

0

2007

2∗∗

3∗∗∗

M-2

M-3

Mai

zeCan

aval

iaN

ole

gum

eVer

mic

om

post

(10

Mg

DM

ha−

1)

9324

80N

PK

909

75N

PK

(50-

10-5

0)+

verm

icom

post

(2.5

Mg

DM

ha−

1)

7311

61

Unfe

rtili

zed

00

0

4∗∗

5∗∗∗

MR-1

MR-2

Mai

ze-

rose

lleCan

aval

iaN

ole

gum

eVer

mic

om

post

(10

Mg

DM

ha−

1)

9324

80N

PK

979

81N

PK

(55-

11-5

5)+

verm

icom

post

7811

66(2

.5M

gD

Mha−

1)

Unfe

rtili

zed

00

0

∗ Exp

erim

ent1

(M-1

mu,M

-1ca

,M

-1nl)

was

setup

inth

evi

llage

ofXal

pat

lahuac

.∗∗

Exp

erim

ents

2(M

-2)

and

4(M

R-1

)w

ere

setup

inth

esa

me

fiel

din

the

villa

geLa

sAnim

as.

∗∗∗ E

xper

imen

ts3

(M-3

)an

d5

(MR-2

)w

ere

setup

inth

evi

llage

Xal

pat

lahuac

.

742

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Maize was sown according to the farmer’s planting pattern and density whichvaried from 1.8 to 5.3 plants per m2 (Flores-Sanchez et al. 2011). Farmersadjusted sowing density to maize variety (wider spacing for land races com-pared to hybrids), available inputs (chemical fertilizers are subsidized for amaximum of two hectares per farm), and current soil nutrient status.

Main plots were 20 m long and 5 m wide. Each subplot (experimentalunit) had an area of 25 m2. Three seeds of the maize “criollo” (local landrace)“Palmeño” were sown manually 5 cm deep in planting holes spaced at 0.70 mwithin the row and 1 m between rows. This corresponded to 4.28 seedsper m2. Sowing was carried out on June 22, 2006. The herbicide Paraquat(1 L ha−1 ) was sprayed 1 week before sowing and 3 weeks after sowingaccording to the farmer’s practice. Organic and mineral fertilizers were onlyapplied to the maize plants. The organic fertilizers were put in the plantinghole during sowing and covered with soil. The inorganic fertilizers urea,di-ammonium phosphate, and potassium chloride were split into two parts:half of the N and all of the P and K were applied at sowing and the rest of theN 6 weeks after sowing (WAS). Mucuna and canavalia were sown 6 weeksafter maize in rows midway between the maize rows spaced at 0.50 m. Theresulting legume density was four plants per m2.

EXPERIMENTS IN 2007

Observations in 2006 confirmed that mucuna’s tendency to climb into themaize plants created problems during harvest. Thus, farmers suggested con-tinuing with canavalia only in 2007. In addition, they suggested including amaize-roselle intercrop.

Cropping systems of maize (M) and maize-roselle (MR) were estab-lished at three experimental sites in the communities of Las Animas andXalpatlahuac (Table 1). Similar to 2006, the experimental design was a split-plot randomized block with three replications. Canavalia and no legumeacted as main plots with four combinations of organic and mineral fertilizersas subplots: 1) vermicompost; 2) mineral NPK; 3) vermicompost + mineralNPK, and 4) unfertilized as control (Table 1). The rates of mineral and organicfertilizers were increased to study the maize response to increased input lev-els. Similar to 2006, experimental units had an area of 25 m2 consisting of fivemaize rows, 5 m long, spaced 1 m apart and plants spaced at 0.7 m withinthe row. Sowing of the maize landrace “Palmeño” took place during the lastweek of June. Maize seed density was again 4.28 per m2. Also for roselle alandrace was used. Roselle (local name Jamaica) was sown one week aftermaize at a rate of three seeds per planting hole located halfway betweentwo maize plants within a row. Thus, interrow spacing for roselle was also0.70 m. The herbicide Paraquat (1 L ha−1) was sprayed twice, 1 week beforeand 3 weeks after sowing. Vermicompost and mineral fertilizers were appliedto the maize and roselle plants. No fertilizers were applied to the canavalia.

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TABLE 2 Soil physical and chemical properties (layer 0–20 cm)

(%) (g kg−1)

Year Exp.Slope(%) Sand Clay Silt

pH(H2O) OM Nt

Bray P-1 mgkg−1

K cmolkg−1

2006 1 21 45 21 34 4.3 17 0.85 15 0.152007 2, 4∗ 5 51 21 28 4.3 11 0.55 15 0.30

3 21 40 23 37 3.7 13 0.50 18 0.635 3 71 19 10 3.3 12 0.50 2 0.06

∗Experiments 2 and 4 were set up in the same field in the village Las Animas.

TABLE 3 Initial chemical composition of the organic fertilizers

g kg −1 (DM)

Year Organic fertilizer N P K pH (H2O)

2006 Goat manure 13.6 0.4 7 8.2Vermicompost 13.2 0.7 6 8.3

2007 Vermicompost 9.3 2.4 8 8.0

Vermicompost was applied in the planting hole before sowing. Mineral fer-tilizers were split into three parts: one third of both N and K, and all of theP were applied in the second week of July; the second dose of N and K wasapplied in the first week of August and the last part at the end of August.Canavalia was sown 4 weeks after maize midway between the main croprows at a rate of two seeds per planting hole with an intra-row spacing of50 cm, resulting in 4 legume plants per m2.

Data Collection

PHYSICOCHEMICAL ANALYSIS OF SOIL AND ORGANIC INPUTS

Soil properties are presented in Table 2 and the chemical composition ofthe organic inputs in Table 3. Soil samples were collected from the surfacelayer (0–20 cm) at each experimental site 2 weeks before sowing maize.The soil properties analyzed were texture (Bouyoucos hydrometer method),pH (1:2 soil to water ratio), organic matter (Walkley-Black method), totalN (Kjeldahl-N method), extractable P (Bray-1 method), and extractable K(NH4OAc, pH 7 method). The organic amendments were analyzed for pH(1:5 compost/manure–water ratio); total N (Kjeldahl method) and total Pand K (inductively coupled plasma spectrometry method) (ICP-AES VarianLiberty II, Varian, Palo Alto, CA, USA) (Alcántar and Sandoval 1999).

MAIZE LEAF AREA INDEX (LAI)

Maize leaf area was estimated at anthesis. Maximum width and length ofthe second leaf below the cob of five plants in each plot were measured.

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The area of the sampled leaf was calculated as maximum width × length ×0.75 (Elings 2000). On the same five plants the number of green leaveswas counted. Since not all the leaves were measured, the area of each leafwas estimated by means of the three parameter normal curve (Landsberg1977). This equation uses the leaf number relative to a reference leaf asinput, along with parameters that describe area of the reference leaf and adispersion parameter σ . Our reference leaf, that is the one with the greatestarea, corresponded to the second leaf below the cob. For σ we used avalue of 3.0, which empirically was found to best describe the data. Leafarea per plant was calculated as the sum of the areas of green leaves, and toestimate LAI the leaf area per plant was multiplied by the number of plantsper square meter.

BIOMASS ESTIMATION

Maize and Roselle. In both years, maize was harvested in the first weekof November (20 WAS). All plants in the central row of each plot wereharvested except the plants located at the edges. Numbers of plants andcobs were counted to calculate their densities. Aboveground fresh weight ofmaize was measured in the field. After cutting plants of the central row threeplants were chosen randomly and oven-dried at 70oC for 24 h to estimateaboveground dry matter (DM) content. The dried plants were separated intograin and straw (combining leaves and stems) and analyzed for N, P, andK. Cobs from the harvested row were weighed and after shelling the maizegrains were oven dried at 70oC for 24 h to estimate grain yield (kg DM ha−1).In the maize-roselle intercrops, roselle was harvested during the first week ofJanuary. The roselle plants were measured from the same central row. Theplants were counted and weighed in the field. Three plants were chosen toestimate plant DM content after oven-drying at 70oC for 48 h. Calyces wereremoved manually from the plants and also oven-dried at 70oC for 24 hto estimate yield (kg DM ha−1). N, P, and K contents were determined onsubsamples of roselle straw (i.e., leaves and stems) and calyces.

Legumes and Weeds. In both years, biomass of legumes as well asweeds was estimated in the second week of January (22 WAS). A quadratof 1 × 1 m2 was placed randomly in each plot. The aboveground biomassof weeds and legumes which were rooted in the square meter includinglegume branches outside that area were collected, separated, and weighed.Subsamples of legumes and weeds were oven-dried at 70oC for 48 h toestimate aboveground yield (kg DM ha−1) and their N, P, and K contentsdetermined. In all samples, total N was analyzed using a semi-micro-Kjeldahlprocedure (Bremner 1965). P and K were analyzed by inductively cou-pled plasma spectrometry (ICP-AES Varian Liberty II) (Alcántar and Sandoval1999).

Dominant Ground Cover Estimation. A quadrat sampling method wasused to estimate dominant ground cover. In both years sampling was carried

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out in the second week of January. Four cover classes were distinguished:crop residues, legumes, weeds and bare soil. A frame of 1 m2 divided into25 smaller squares (0.20 × 0.20 m2) was placed randomly along the centralrow of each subplot (experimental unit). In all squares the dominant coverclass was visually assessed and recorded. Dominant ground cover (%) perclass (x) was estimated as: 100 × (# dominant squares of class (x) / total #squares).

Nutrient Uptake. Total N, P, and K uptake from all the sources at thecropping system level was calculated by summing the aboveground N, P,and K uptake by weeds, maize, roselle, and legumes.

Statistical Analysis

Data from subplots were pooled to obtain averages and an analysis of vari-ance (ANOVA) was carried out per experiment to analyze main plot effects(2006) and effects of main plot and location (2007) using SAS 9.1 (SASInstitute 2002). Means separation was performed by Tukey’s standardizedrange (HSD) test when the F test indicated significant (P < 0.05) differencesamong the treatments.

RESULTS

Effects of Intercropping Legumes on AbovegroundBiomass and Main Crop Yields

Aboveground biomass of maize was not affected by legume intercrops nei-ther in the maize monoculture nor in the maize-roselle mixture (Figure 1).In 2006, maize aboveground biomass ranged from 3871 to 4300 kg DMha−1 (Figure 1a), while in 2007 it was between 2973 and 11051 kg DMha−1 (Figure 1b). In the case of roselle, in treatment MR-1 abovegroundbiomass was significantly higher in the presence of canavalia compared tothe monocrop (Figure 1c). In both years there were no significant interactions(P < 0.05) between the factors legumes and sole maize and maize-roselleand the nutrient amendment treatments (data not shown).

In both years, intercropping did not affect grain yield in the maizemonoculture or in the maize-roselle mixture. In 2006, maize grain yield wasnot affected by legume type (Figure 2a). In 2007, maize grain yields variedamong experimental sites between 508 and 2867 kg DM ha−1 (Figure 2b),and calyx yields varied between 57 and 121 kg DM ha−1 (Figure 2c). In MR-1,calyx yield was increased by canavalia as the intercrop. There was a signif-icant effect of experimental site for both experiments. Treatments M-2 andMR-1 (site 2) had the highest values of maize grain yield, while the lowestones were found in MR-2 (site 5). However, roselle calyx yield was highestin the latter case.

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0

4000

8000

12000

M-2 M-3 MR-1 MR-2

Mai

ze a

bove

grou

nd b

iom

ass

(kg

DM

ha–1

) (B)

0

400

800

1200

MR-2MR-1

Ros

elle

abo

vegr

ound

bio

mas

s (k

g D

M h

a–1)

a

b

(C)

0

2000

4000

M-1nl M-1mu M-1ca

Mai

ze a

bove

grou

nd b

iom

ass

(kg

DM

ha–1

)

without legumes with legumes

(A)

FIGURE 1 Mean (±SE) aboveground biomass of maize (kg DM ha−1), (A) 2006, (B) 2007,and (C) roselle (kg DM ha−1), with and without intercropping with legumes. Different lettersdenote significant differences between treatments (P < 0.05).

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0

2000

M-2 M-3 MR-1 MR-2

Gra

in y

ield

(kg

DM

ha–1

)

(B)

0

50

100

MR-1 MR-2

Cal

yx y

ield

(kg

DM

ha–1

)

b

a

(C)

0

2000

M-1nl M-1mu M-1ca

Gra

in y

ield

(kg

DM

ha–1

)

without legumes with legumes

(A)

FIGURE 2 Mean (±SE) maize grain yield (kg DM ha−1), (A) 2006, (B) 2007, and (C) rosellecalyx yield (kg DM ha−1), with and without intercropping with legumes. Different lettersdenote significant differences between treatments (P < 0.05).

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Effects of Intercropping Legumes on Leaf Area and LAI

Only in M-2 there was a significant but small difference in leaf area betweentreatments with and without legume (Table 4). In the other treatments, leafarea was not affected due to the inclusion of legumes. In addition, thenumber of leaves and LAI was also not affected by intercropping legumes.In 2006, the estimated LAI ranged from 0.8 to 0.9. This was lower than in2007 where LAI values varied between 1.1 and 2.0.

Biomass of Legumes

In 2006, mean accumulated aboveground biomass of mucuna and canavaliaat 22 WAS was 1797 and 2257 kg DM ha−1, respectively (Figure 3a). However,this difference was not significant. In 2007, accumulated abovegroundbiomass of canavalia at 24 WAS in maize monoculture (M-2 and M-3) rangedfrom 1805 to 2082 kg DM ha−1, while in the maize-roselle mixture (MR-1 andMR-2) it varied little from 960 to 1000 kg DM ha−1 (Figure 3b).

Weed Biomass and Ground Cover

Weed aboveground biomass was consistently lower in the presence oflegumes. In 2006, canavalia and mucuna caused a weed biomass reductionof 24% and 55%, respectively, compared to the maize monocrop (Figure 3a).The highest dominant weed ground cover was found in maize as monocrop(66%; Table 5), whereas it was reduced to only 17 and 26% in the presenceof canavalia and mucuna, respectively.

In 2007, canavalia showed again a weed suppressing effect in maizeand maize-roselle cropping systems (Figure 3b). In M-2, M-3 and MR-1 theinclusion of canavalia reduced significantly the weed biomass by 39% to45% compared to the maize monocrop. In MR-2, the reduction of weedbiomass was 26%, but not significant. Dominant weed ground cover in themaize monocrop was about 80% (Table 5), and in maize intercropped withcanavalia it ranged between 22% and 27%. In the maize-roselle intercropdominant weed cover was reduced from 79% to 39% in MR-1, and from58 to 48% in MR-2.

Residual Aboveground Biomass and Nutrient Uptake

In 2006, the average difference in residual biomass between plots withlegumes and without legumes was significant; in 2007 differences weresmaller and not significant (Table 6).

For both years, the inclusion of legumes into the maize andmaize-roselle cropping systems increased significantly total N, P, and Kuptake by 52%, 24%, and 30%, respectively (Table 7). In 2006, canavalia

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TAB

LE4

Mea

n(±

SE)

mai

zele

afar

ea(c

m2)

of

the

seco

nd

leaf

bel

ow

the

cob,num

ber

of

gree

nle

aves

atta

ssel

ing

stag

e,pla

ntden

sity

and

leaf

area

index

with

and

with

out

inte

rcro

ppin

gw

ithle

gum

es.D

iffe

rent

letter

sden

ote

sign

ifica

nt

diffe

rence

sdue

toin

terc

roppin

g(P

<0.

05)

Leaf

area

(cm

2)

Num

ber

ofle

aves

Pla

ntden

sity

(m2)

Est

imat

edLA

I

Yea

rCode

With

legu

me

With

out

legu

me

With

legu

me

With

out

legu

me

With

legu

me

With

out

legu

me

With

legu

me

With

out

legu

me

2006

M-1

mu

529

(±48

)48

4(±

46)

11(±

0.46

)10

(±0.

50)

3.08

(±0.

23)

3.01

(±0.

12)

0.9

0.8

M-1

ca48

6(±

40)

484

(±46

)10

(±0.

43)

10(±

0.50

)3.

13(±

0.16

)3.

01(±

0.12

)0.

90.

820

07M

-279

3a

758

b12

(±0.

27)

12(±

0.37

)4.

23(±

0.15

)4.

29(±

0.18

)2.

01.

9M

-364

3(±

43)

661

(±54

)11

(±0.

35)

11(±

0.51

)4.

25(±

0.10

)4.

28(±

0.16

)1.

61.

6M

R-1

793

(±25

)78

1(±

15)

12(±

0.51

)12

(±0.

43)

4.28

(±0.

08)

4.30

(±0.

17)

2.0

2.0

MR-2

474

(±14

)45

8(±

19)

10(±

0.25

)10

(±0.

28)

4.28

(±0.

11)

4.27

(±0.

17)

1.2

1.1

750

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] at

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0

1000

2000

M-2 M-3 MR-1 MR-2

Acc

umul

ated

bio

mas

s (k

g D

M h

a–1)

a

b

a

b

a

b

(B)

(A)

0

1000

2000

M-1nl M-1mu M-1ca

Acc

umul

ated

bio

mas

s (k

g D

M h

a–1)

Weed biomass with legumes

Weed biomass without legumes

Legume biomass

a

bab

FIGURE 3 Mean (±SE) aboveground biomass of weeds (kg DM ha−1), and legumes (kgDM ha−1), (A) 2006, (B) 2007 with and without intercropping with legumes. Different lettersdenote significant differences between treatments (P < 0.05).

had a much higher N and K uptake than mucuna. In 2007, total N, P, and Kuptake was clearly higher with maize as monocrop (M-2 and M-3) than in themaize-roselle intercrops (MR-1 and MR-2). This difference was linked to thehigh amount of canavalia biomass found in the maize monocrop (Figure 3b).

DISCUSSION

The results of the study demonstrate that sowing of Mucuna pruriensvar. utilis and Canavalia brasiliensis Mart. ex Benth 4–6 weeks after themain crops resulted in important agroecological benefits in maize and

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TABLE 5 Mean (±SE) percentage of dominance in ground cover by legumes, weeds, cropresidues, and bare soil at the end of growing season with and without intercropping withlegumes

(%)

Year Code Treatment Legume Weeds Crop residues Bare soil

2006 M-1mu mucuna 36 (±6) 26 (±5) 20 (±3) 18 (±5)M-1ca canavalia 61 (±3) 17 (±4) 11 (±4) 11 (±4)M-1nl no legume 0 66 (±4) 28 (±4) 6 (±2)

2007 M-2 canavalia 56 (±6) 27 (±4) 14 (±3) 3 (±1)no legume 0 80 (±2) 13 (±2) 7 (±1)

M-3 canavalia 54 (±5) 22 (±4) 17 (±5) 7 (±2)no legume 0 82 (±4) 15 (±3) 3 (±2)

MR-1 canavalia 35 (±3) 39 (±5) 19 (±3) 7 (±3)no legume 0 79 (±2) 15 (±2) 6 (±2)

MR-2 canavalia 23 (±3) 48 (±7) 10 (±2) 19 (±5)no legume 0 58 (±5) 19 (±4) 23 (±4)

TABLE 6 Mean total remaining aboveground biomass (kg DM ha−1) at the end of grow-ing season with and without intercropping with legumes. Different letters denote significantdifferences due to intercropping (P < 0.05)

Residual aboveground biomass∗

Year Code with legume without legume difference % increase

2006 M-1mu 4818 a 3219 b 1599 33M-1ca 5034 a 3219 b 1815 36

2007 M-2 7889 a 6698 a 1191 15M-3 5668 a 4771 a 897 16MR-1 10168 a 8512 a 1656 16MR-2 4698 a 4182 a 516 11

∗Components of remaining aboveground biomass: maize and roselle crop residues (stems and leaves),legumes, and weeds.

maize-roselle cropping systems in the Costa Chica. Compared to conven-tional practice, undersowing of legumes did not result in yield loss in themain crops due to competition, weed biomass was reduced, total biomass ofcrop residues was higher and N, P, and K yields were increased both due toN2 fixation from the atmosphere and enhanced N, P, and K uptake from thesoil. In this section we relate our findings to other reports on intercroppinglegumes in tropical maize, discuss the on-farm methodology and draw outconsequences for cropping systems in the Costa Chica region.

Effects of Intercropping Legumes on Main Crop Yields

Competition between the intercrop and the main crops maize and rosellewas avoided due to delayed sowing of the legumes and low planting den-sity of the main crops. Appropriate choice of sowing date is a key tosuccessful intercropping systems (Akanvou et al. 2002). Even though we

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TAB

LE7

Mea

nto

talN

,P,

and

Kupta

ke(k

gha−

1)

of

bio

mas

sof

mai

ze,ro

selle

,le

gum

esan

dw

eeds

atth

een

dof

grow

ing

seas

on.D

iffe

rent

letter

sden

ote

sign

ifica

ntdiffe

rence

sdue

toin

terc

roppin

g(P

<0.

05)

Tota

lN

upta

ke(k

gN

ha−

1)

Tota

lP

upta

ke(k

gP

ha−

1)

Tota

lK

upta

ke(k

gK

ha−

1)

Yea

rCode

with

legu

me

with

out

legu

me

Diffe

rence

(%)

with

legu

me

with

out

legu

me

Diffe

rence

(%)

with

legu

me

with

out

legu

me

Diffe

rence

(%)

2006

M-1

mu

47a

34b

3812

a9b

3350

a35

b43

M-1

ca70

a34

b10

612

a9b

3361

a35

b74

2007

M-2

94a

64b

4732

a24

b33

54a

47b

15M

-371

a43

b65

16a

13b

2341

a35

b17

MR-1

97a

80b

2136

a34

b6

71a

65b

9M

R-2

52a

39b

3314

a12

b17

29a

24b

21Ave

rage

5224

30

753

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ded

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Lib

rary

] at

06:

25 3

0 A

ugus

t 201

3


did not evaluate the effects of sowing date explicitly, our results indicatedthat a delay in sowing of 4 weeks was long enough to avoid interspe-cific competition for light and nutrients and allow a good establishment ofboth maize and roselle. These results are in agreement with similar stud-ies in different tropical environments (Gitari et al. 2000; Akanvou et al.2002; Eilittä et al. 2003; Arim et al. 2006; Monneveux et al. 2006). Otherstudies showed that sowing legumes 2 or 3 weeks after maize did reducemaize yield in a number of cases (Fischler and Wortmann 1999; Gacheneet al. 2000; Kirchhof and Salako 2000; Chikoye et al. 2002; Mureithi et al.2005; Lawson et al. 2007). Optimizing sowing date would require localexperiments, preferably supported by model-based analyses to exploresowing strategies under different weather conditions (Kropff and Spitters1991).

Plant density affects both intra- and interspecific competition and hasparticularly a strong effect on grain yield of maize (Sangoi 2001). Final plantdensity in 2006 (3.01 m2) and 2007 (4.27 m2) was within the range of 1.8 to5.3 m2 found in farmers’ fields (Flores-Sanchez et al. 2011). The associatedLAI values at anthesis of 0.8 and 2.0 (Table 4) confirm that these plantingdensities are low. Currently, farmers consider higher planting densities notfeasible since these would require higher inputs of fertilizers for which therequired cash is not available.

The scant literature on roselle mostly reports about intercropping withlegumes such as groundnut and cowpea (Sermsri et al 1987; Fbabatunde2003). Fbabatunde (2003) demonstrated that roselle is more compatible withlegume intercrops than with cereals probably due to light competition inthe latter case. In our experiments, roselle responded positively to legumeintercropping in MR-1, but was just as for maize not affected in MR-2.

Experiments M-2 and MR-1 gave similar grain yields that were at leasttwice the average value obtained in experiments M-3 and MR-2. Legumebiomass did not follow this pattern, with M-2 and M-3 having higher biomassthan MR-1 and MR-2. Weed biomass did not differ between similar treatments(i.e., with and without legumes) across sites. In MR-1, roselle calyx yield wasincreased due to the presence of canavalia, while in MR-2, the least fertilesite, maize biomass, and grain yield remained low. However, here the soilproperties were better for the performance of roselle. This crop tolerates awide range of pH values, due to its tap root system having a good capacity toexplore belowground sources in the deeper soil layers (McLean 1973; Fadland Gebauer 2004). In view of the importance of roselle as a cash crop,further elaboration of the competition in the three-crop species mixture isnecessary.

Nutrient Contribution to the System and Nutrient Uptake

The steep slopes in the study area and the predominantly sandy soils leadto a risk of nutrient runoff, and soil erosion, as well as N and K leaching

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losses. Legumes as a catch crop can reduce nitrate (Thomsen and Christensen1999; Vos and van der Putten 2004) and K leaching (Askegaard and Eriksen2008). In our study intercropping legumes caused an increase in accumu-lated total biomass of up to 36% (Table 6) and N, P, and K uptake (Table 7).These findings indicate that both legumes acted not only as a N2 fixingcrop but also as a catch crop by taking up additional soil mineral N, P,and K. According to expectations, aboveground biomass of canavalia andassociated nutrient uptake was higher than that of mucuna. Also, NPK con-centrations in the plant tissues of canavalia exceeded those of mucuna (datanot shown). A deeper root system and better adaption to the marginal acidsoils (Peters et al. 2003) certainly could have contributed to canavalia’s bet-ter performance. Comparing five annual legumes for fixation of atmosphericnitrogen, soil water uptake, soil P and nitrate recovery, effects on subsequentcrops and for phosphorus recovery from Busumbu P rock, Wortmann et al.(2000) also found that canavalia produced the most biomass, fixed the mostN2, was most efficient in extraction of soil nitrate, and supplied most N tosubsequent maize and bean crops.

The introduction of legumes described in this study can be seen asan example of ecological complementarity (Erskine et al. 2006; Malézieuxet al. 2009). Complementarity may arise from different exploration pat-terns of the soil profile by the different plant species, and by the differentsowing dates. In our study, overall productivity of the system increaseddue to the presence of the legumes because they also contributed to anincreased N, P, and K uptake from the soil. These findings make legumesan important tool in the studied cropping systems where N and K arethe major yield limiting factors (Flores-Sanchez et al. 2011; Flores-Sanchez,2013).

Legume Agronomy

Canavalia accumulated 20% more biomass than mucuna in 2006, althoughthe difference was not significant. Also because of its prostrate growth habit,canavalia was the agronomically preferred species in 2007. The climbinggrowth habit of mucuna was found to be unattractive by farmers, whoneeded to slash the vines to harvest maize as also reported by other authors(e.g., Nyende and Delve 2004). Important for its deployment in the CostaChica is the additional fact that canavalia as opposed to mucuna is welladapted to acid soils (Carsky et al. 2001; Kaizzi et al 2004), and to low soilfertility conditions in general (Peters et al. 2003; Martens et al. 2008). Despiteits slow initial establishment due to a high level of hardseededness, canavaliacan develop an extensive root system (Alvarenga et al. 1995).

Another useful characteristic is that the leaves of canavalia remain greenand turgid until well into the dry season. In our experiments the Januarysampling revealed fully green plants of canavalia, while mucuna was with-ered and dry. When canavalia is grazed it can regrow during the dry season

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(Douxchamps et al. 2010), thus both providing soil cover during the firstrains in June and serving as a source of animal feed (Martens et al. 2008).Besides, several studies revealed that canavalia leaves contain chemicalcompounds which can inhibit the growth and development of leaf-cuttingants, a common pest of roselle in Costa Chica, and inhibits the symbioticfungus development needed by these ants (Hebling et al. 2000; Sridhar andSeena 2006; Valderrama-Eslava et al. 2009).

Intercropping with legumes that provide similar agro-ecological benefitsfor the cropping systems (e.g., catch crop, soil cover etc.) but in additionalso provide a source of additional income for farmers requires attention.Currently, options to sell products like beans are however limited due tolack of marketing infrastructure (Flores-Sanchez et al. 2011).

Legume Effects on Weed Biomass

Weed biomass reduction was a clear positive benefit of intercroppinglegumes in maize and maize-roselle cropping systems. First year effectsshowed weed biomass reductions between 24 and 45% compared to the non-legume treatments. Other authors found similar or stronger effects (SkóraNeto 1993; Akobundu et al. 2000; Favero et al. 2001; Lawson et al. 2007).In 2006, mucuna was more effective in weed reduction than canavalia. Thistrend may be linked to its growth characteristics. Mucuna had a relatively fastearly growth followed by fast senescence. Weed suppression was linked toshading, and fallen leaves created a ground litter layer of mulch that smoth-ered weeds. Several studies have demonstrated that residue decompositionof mucuna inhibits weed biomass growth due to allelopathic and phy-totoxic compounds (L-3,4-diydroxy-phenylalanine). Thus, competition andallelopathic effects may have acted simultaneously to reduce weed biomassproduction (Fujii et al. 1992; Anaya 1999; Nwaichi and Ayalogu 2010).

Intercropping with legumes may also contribute to a long-term weedmanagement strategy. Reliance on herbicides will decrease as a result ofreduced weed seed production and a gradual depletion of viable seeds inthe soil seed bank. Legume residues generally create a mulching layer thatincreases the physical barrier for early germination (Teasdale et al. 2007;Bastiaans et al. 2008). Such effects do require sufficient residual organicmaterial on the soil surface at the start of the new rainy season, which notonly depends on the amounts produced and the speed of decomposition(Flores-Sanchez 2013) but also on removal by cattle. In the Costa Chica, it iscommon to have animals roaming the fields in the dry season and removingorganic residues.

The absence of negative effects on crop yields and the obvious reduc-tion of weed biomass in the year of implementation constitute importantprerequisites for adoption by farmers. Longer term positive effects of soilcover by organic residues on erosion and weed dynamics, and effects on

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physical and chemical soil fertility by larger organic matter additions to thesoil remain to be investigated.

CONCLUSION

Mucuna and canavalia sown as cover crops 4–6 weeks after maize did notdecrease yield of maize or roselle grown under current farmer practices inthe Costa Chica. Both legumes contributed to the reduction of weed biomass.This opens up perspectives for weed management strategies with reducednumber of herbicide applications. Canavalia was found to perform betterthan mucuna in terms of biomass accumulation, nutrient uptake, and ease ofhandling. We conclude that inclusion of legumes in maize cropping systemsin the Costa Chica is a promising low-cost option to increase N input andreduce nutrient losses.

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Exploring Maize-Legume Intercropping Systems in Southwest Mexico

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