Nematode infestation and N-effect of legumes on soil and crop yelds in legume-sorghum rotations

doi:10.4236/as.2011.22008

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Vol.2, No.2, 49-55 (2011) Agricultural Sciences

doi:10.4236/as.2011.22008

Nematode infestation and N-effect of legumes on soil

and crop yields in legume-sorghum rotations

Vincent Bado1*, Abdoulsalam Sawadogo2, Bouma Thio2, André B ationo3, Karim Traoré2,

Michel Cescas4

1Africa Rice Center (AfricaRice), Sahel Regional Station , Saint Louis , Senegal; *Corre sponding Author: [email protected]

2Institut de l'Environnement et de Recherches Agricoles, Bobo-Dioulasso, Burkina Faso;

3The Tropical Soil Biology and Fertility Institute of International Center for T ropical Agriculture, Nairobi, Kenya;

4Département des Sols et Génie Agroalimentaire (FSSA), Université Laval Ste Foy Québec, Qué bec, Canada.

Received 28 June 2010; revised 24 March 2011; accepted 31 March 2011.

ABSTRACT

The effects of cowpea (Vignaunguiculata) and

groundnut (Arachis hypogea) on succeeding

sorghum yields, soil mineral N and nematode in-

festation were studied during five cropping sea-

sons (2000 to 2004) in a weakly acid Ultisol of

the agronomy research station of Farakô-Balo-

cated in the Guinean zone of Burkina Faso, West

Africa. A factorial 5 × 5 design of five crop rota-

tions with five fertilizer treatments in a split-plot

arrangement with four replications was used.

Sorghum yields were affected by the two factors

(rotation with legumes a nd fe rti l izer a ppl ications)

during the four years. But interactions were not

observed between the two factors. Monocrop-

ping of sorghum produced the lowest yields and

legume-sorghum rotations increased sorghum

yie l d s by 50% to 300%. Groundnut-sorghum and

cowpea-sorghum rotations increased soil mi-

neral N by 36% and 52%, respectively. Crop ro-

tation influenced nematode infestation but the

effects on soil and sorghum root infestation dif-

fered according to the rotation. The cowpeasor-

ghum rotation increased soil and sorghum root

infestationby nematodes while groundnut-sor-

ghum decreesed the nematode population. The

soil of the cowpea-sorghum rotation contained

1.5 to 2 times more nematodes than the soil of

the monocropping of sorghum. In contrast, the

soil of the groundnut-sorghum rotation con-

t ai ned from 17 to 19 tim es fewer nematodes than

that of themonocropping of sorghum. However,

nematode infestation did not affect any of the

succeeding sorghum yields. It was concluded

that the parasitic effect of nematodes was lim-

ited by the predominance of positive N-effects

on the development of succeeding sorghum.

Keywords: Legume; Nematode; Nitrogen; Crop

Rotation; Sorghum

1. INTRODUCTION

In sub-Saharan Africa, crop yields are limited by

many factors such as nutrient deficiencies. Soils have

inherently low levels of nutrients because of low soil

organic matter levels and limited use of nutrient inputs

by farmers. Nitrogen (N) and phosphorous (P) deficien-

cies are the main soil fertility constraints in most of the

soils of West Africa [1]. Chemical fertilizers are im-

ported from developed countries and remain expensive

for poor small holders who therefore never use them or

only occasionally apply small quantities. While 73

kg·ha-1 of chemical fertilizers are used by farmers in

Asia, only 8 kg·ha-1 are used in Africa [2]. N2-fixing

legume crops can help improving soil fertility as sources

of nitrogen. Some legume crops such as groundnut

(Arachis hypogea L.) and cowpe a (Vignaunguiculata (L.)

Walp) are traditionally cultivated by farmers in rotation

or intercropping with cereals. Legume crops can supply

N for non-fixing cereals via biological nitrogen fixation.

In cropping syste ms, N2-fixing legumes can supply N to

the subsequent crops through fallen senescent leaves and

below ground parts, leading to an increase in succeeding

crop yield [3-5]. However, the improvement of soil N

content by legumes also creates favourable conditions

for the development of soil fauna such as parasitic ne-

matodes that could affect the succeeding crop. Some

legumes such as groundnut can reduce the population of

nematodes, while other legumes can increase nematode

infections [3]. In legume-cereal rotations, we can hypo-

thesize that a high population of parasitic nematodes

induced by a previous legume could probably reduce the

V. Bado et al. / A gricultural Sciences 2 (2011) 49-55

development, N absorption (or N-effect) and the yields

of the succeeding crop. Conversely, legumes that can

reduce nematode infestation such as groundnut should

probably have a better N-effect on the succeeding crop.

Little research has been oriented on the interaction of

N-effect and nematode induced by legumes on soil and

succeeding crop. This research aimed to study the com-

bined effect of the two factors (N and nematode infesta-

tion) on soil and succeeding crop.

2. MATERIALS AND METHODS

The study was undertaken through field experiments

carried out over five year s (2000-2004) at the agrono mic

research station of Farakô-Ba (4°20'West, 11°6'North

and 405 m altitude), located in the Guinean savannah

zone of Burkina Faso. This agro ecological zone has one

rainy season per year, starting in May-June and ending

in October. During the five cropping seasons of the ex-

periment, annual rainfall during the cropping seasons

varied from 1058 mm in year 2000 to 639 mm in year

2002 (Table 1). In general, planting dates occurred in

June and harvesting was carried out in October. The ex-

periment was laid down on a six -year-old fallow area on

an Ultisol, a weakly acid (pH/KCl: 5.6) sandy soil (74%)

with low clay (7%) and organic carbon (0.6%) contents.

Available P (P-Bray I: 5.6 mg·kg–1), Ca, Mg and ex-

changeable K and exchange capacity (ECEC: 1.8 coml.

+ kg–1 soil) were very low.

Two legume crops: groundnut (Arachis hypogea L.)

and cowpea (Vignaunguiculata (L) Walp) were used.

Improved varieties of groundnut (RMP-12) and cowpea

(KVX-61-1) recommended by the national agronomic

research institute (INERA) for the Guinean savannah

zone were sown with, respectively, planting densities of

62,500 and 125,000 plants per hectare. An improved

variety of sorghum (Sariaso) with a planting density of

62,500 plants per hectare was used.

A factorial 5 × 5 experiment in a split-plot experi-

mental design with randomised block arrangement and

four replications was used. The five crop rotations (Ta-

ble 2) were used as first factor in the main plots. Each

main plot was split intofive sub plots for different fer-

tilization treatments (PK, NPK, NPK + Dolomite, NPK

+ Manure and Control) employed as second factor.

Chemical fertilizers were applied at rates of 14 kg N ha–1,

10 kg P ha–1 and 11 kg K ha–1 to the two legumes using

complex NPK fertilizer, triple super phosphate and po-

tassium chloride. For the manure-containing treatments,

three tonnes per hectare of air-dried cattle manure were

applied. Cattle manure contained 1.8%, 18.40%, 0.31%

and 0.16%, respectively, of N, C, P and K. In the dolo-

mite-containing treatments, one tonne ha–1 of dolomite

(249 kg ha–1 of Ca and 114 kg ha–1 of Mg) were used.

Except for urea, all fertilizer s were applied at sowing.

Nitrogen fertilizers were split on sorghum plots: 14 kg

N–1 with NPK fertiliser at sowing and 23 kg N ha–1 40

days after sowing (DAS). Legumes were not inoculated.

As regards farmer ’s traditional practices, the residues of

Table 1. Monthly and annual rainfall at Farakô-Ba during the five years of the ex-

periment.

Years

Months

Total

May

June

July

August

September

October

2000 60 172 236 309 241 41 1059

2001

154

229

153

715

2002 58 65 184 175 125 32 639

2003

11 3

244

243

839

2004

152

161

178

344

268

1201

Mean

11 8

170

260

206

Table 2. Rotation of the three crops of the six treatments during the five years (2000-2004) of ex-

perimentation.

Years

Crop rotations

2000

2001

2002

2003

2004

Cowpea-sorghum

Cowpea

Sorghum

Cowpea

Sorghum

Cowpea

Sorghum-cowpea

Sorghum

Cowpea

Sorghum

Cowpea

Sorghum

Groundnut-sorghum

Groundnut

Sorghum

Groundnut

Sorghum

Groundnut

Sorghum-groundnut Sorghum Groundnut Sorghum Groundnut Sorghum

Sorghum-sorghum

Sorghum

V. Bado et al. / Agricultural Sciences 2 (2011) 49-55 51

sorghum and legumes are exported at the end of each

season. Only the senescent leaves and residues of roots

of the below ground parts remain as a source of organic

residues recycled in the soil.

The N-effects of legumes were evaluated by soil N

mineralization (

NH+

−

) during the first two

months of the second cropping season (2001) after one

season of rotation. Soil samples were taken in the first

20 cm layer at sowing, 9, 20, 30, 40 and 53 days after

sowing. All sub-plots of the five fertilizer treatments

were sampled. Soil samples were taken in sorghum

plots of three rotations (sorghum-sorghum, cowpea-

sorghum and groundnut-sorghum). Mineral N was ex-

tracted with 1M KCl solution and measured by the col-

orimetric method [6].

Nematode populations were assessed dur ing the crop-

ping season of 2001. All sub-plots of the five fertilizer

treatments were sampled. Soil samples were taken in

sorghum plots of the three rotations (sorghum-sorghum,

cowpea-sorghum and groundnut-sorghum). Soil and root

samples of sorghum were removed at 30 and 90 days

after sowing, and nematodes were extracted and meas-

ured using the methodology described by Seinhorst [7].

Many zero values and high coefficient of variation were

observed, particularly on sorghum root infestation by

nematodes. Thus, logarithmic function Eq.1 was used

for data transformation before statistic analysis [8].

y = log x + 1 (1)

x was the number of nematodes and y the transformed

value.

Agronomic data of sorghum yields were first analyzed

per year using the Fisher test for comparison of treat-

ment effects [8]. Then, the global effects of the four

years were analyzed using the year as a factor. The rota-

tions and fertilizers were used as first and second factors,

respectively.

3. RESULTS AND DISCUSSIO NS

3.1. Nematode Infestation

The effects of crop rotations on soil and sorghum

roots infestation by nematodes are presented on (Table

3). Fourgroups of nematodes (Pratylenchus, Scutel-

lonema, Helycotylenchus and Trychodorus) were identi-

fied in the soil. The two most important groups identi-

fied in the soil were Helicotylenchus (55%) and Scute-

lonema (34%). But only two groups (Pratylenchus and

Scutelloma) were identified on sorghum roots. However,

sorghum roots were mainly infested by Pratylenchus

(80%) and Scutelonema (20%) at 30 days after sowing

and by Pratylenchusonly at 90 days after sowing. But

soil and roots infestation by nematodes was not affected

by fertilizer application (data not shown). Only crop

rotation affected soil and roots infestation (p < 0.01) by

nematodes and interactions were not observed between

these two factors. Otherwise, variation in the populations

of nema t ode s wa s due to crop r ot a tions.

Groundnu t and cowpea had opposite effects in the soil

and on the succeeding sorghum root infestation by

nematodes. Compared to the groundnut-sorghum rotation,

a cowpea-sorghum rotationincreased soil (p < 0.01) and

sorghum roots (p < 0.01) infestationby the three groups

of nematodes (Pratylenchus, Scutellonema, Helycotylen-

chus). The soil of the cowpea-sorghum rotation contained

1.5 to 2 times more nematodes than the soil used for-

mono cropping of sorghum. As for cowpea-sorghum ro-

tation, the monocropping of sorghum also increased the

population of Pratylenchus and Scutellonemain the soil

and differences were not observed between the two rota-

tions. On the other hand, groundnut decreased the inci-

dence of the four nematodes in the soil. In ground-

nut-sorghum rotations, the soil contained from 17 to 19

times fewer nematodes than cowpea-sorghum and Môn

croppedsorghum.

3.2. Soil Mineral Nitrogen

For all rotation treatments, soil mineral N decreased

rapidly during the season (Fi g u re 1 ). The first rains of the

season induced a resurgence of microbial activity leading

to a “mineralization flush” of soil organic nitrogen and

increases in mineral N. The mineral N decline can be ex-

plained by the decrease of the mineralization of soil or-

ganic residues, by N uptake by plants, N leaching and

other losses of N. The mineralization of soil organic resi-

dues started with the first rains of the season and de-

creased over time, as indicated by mineral N decreases.

Throughout the season, fertilizer applications did not

affect soil mineral N. However, soil mineral N was af-

fected (p < 0.05) by crop rotation at the start of season (1 -

20 days after sowing) and no interaction was observed

between fert il ize r a nd rotation. During thi s fi rst pe riod ( 1 -

20 days after sowing), the presence of legumes in the

cropping systems increased soil mineral N (p < 0.05) and

differences were not observed between the two legumes

(Fig ure 1). At sowing, soil mineral N varied from 4 2 k g N

ha–1 in monocropping of sorghum to 55 and 62 kg N ha–1

when sorghum was rotated with groundnut and cowpea,

respectively. Otherwise, groundnut-sorghum and cow-

pea-sorghum rotations increased soil mineral N from 36%

and 52%, respe cti vely.

3.3. Sorghum Yields

During the first season (absence of rotation effect),

only the effects of fertilizers were measured. The effects

52 V. Bado et al. / Agricultural Sciences 2 (2011) 49-55

Table 3. Effects of crop rotation with legumes (groundnut-sorghum, cowpea-sorghum) and monocropping of sorghum on soil

(nematodes/dm3 of soil) and sorghum roots (nematodes/g) infestationby nematodes at 30 and 90 days after sowing in 2001.

Nématodes

Daysaftersowing Croprotations Pratylenchus Scutellonema Helycotylenchus Trychodorus Total

Nematodes in

the soil

Groundnut-sorghum 5 c 130 c 97 c 62 b 158 c

Cowpea-sorghum

157 ab

1138 ab

3157 a

55 bc

3212 a

Sorghum-sorghum 175 a 1228 a 843 b 377 a 1220 b

Groundnut-sorghum

53 c

135 c

510 c

207

905 c

Cowpea-sorghum

518 a

1213 a

3532 a

618

5880 a

Sorghum-sorghum

407 ab

940 ab

1892 b

122

3360 b

Nematodes in

sorghum roots

Groundnut-sorghum 8 c 4 c 0 0 12 c

Cowpea-sorghum

389 a

60 ab

449 a

Sorghum-sorghum

160 ab

72 a

232 ab

Groundnut-sorghum

4 c

90 Cowpea-sorghum 109 a 0 0 0 109 a

Sorghum-sorghum

69 ab

Values affected by the same letter in the same column are not significantly different at p < 0.05, according to Fisher’s test

19 2030 40 53

D a ys after sowing

Kg N ha-1

Groundnut-Sorghum

Cowpea-Sorghum

Sorghum-Sorghum

Figure 1. Effects of monocropping of sorghum, cowpea-sorghum and groundnut-sorghum

rotations on soil mineral N during the 53 days after sowing in year 2001.

of rotations were evaluated over the next four years

(2001-2004). Sorghum grain yields were affected (p <

0.001) by fertilizer applications, crop rotations and years

(Fi g u re s 2 and 3). However, interactions were not ob-

served between rotations and fertilizers, indicating that

previous legumes (rotations) affected sorghum yields

whether fertilizers are applied or not, and conversely.

Interaction was not observed between year and fertilizer,

showing good responses to fertilizer whatever the rain-

fall in a given seaso n.

During the first year, sorghum produced high yields

even when fertilizers were not applied wh ile yields were

very low during the final two years (Fi gu re 2). This can

be explained by the positive effects of the previous fal-

low in the first year of cultivation and the subsequent

nutrient decrease. In the absence of fertilizer, soil nutri-

ents are exported, leading to declining fertility and yield

decrease during the next four years [9]. Chemical NPK

fertilisation alone increased sorghum grain yields in the

presence of this low soil fertility, thereby indicating

good response to chemical fertilizer [1,9,10]. Applica-

tion of chemical NPK fertilizer associated with manure

produced the highest yields during the five years of this

experiment. Similar results relating to the beneficial ef-

fects of chemical and organic fertilizers on crop yields

have been reported, although they are usually attributed

to the role of organic materials both in correcting soil

acidity and acting as a source of nutrients [1,9,11].

Kg N ha

–1

V. Bado et al. / Agricultural Sciences 2 (2011) 49-55 53

500

1000

1500

2000

2500

2000 2001 2002 2003 2004

Years

Grain yields (kg ha-1)

NPK

NPK+D

NPK+M

Control

Figure 2. Effect of fertilizer applications on three rotations (cowpea-sorghum, groundnut-sorghum and sorg-

hum-sorghum) on sorghum grain yields during four years (2001-2004).

Cow- So r g

Grou-Sorg

Sorg-Sorg

Cr op Rota tion s

1000

2000

3000

Grain Yields (kg ha-1)

Cow- So r g

Grou-Sorg

Sorg-Sorg

Cr op Rota tion s

1000

2000

3000

4000

Grain Yields (kg ha-1)

Cow-Sorg

Grou-Sorg

Sorg-Sorg

Cr op Rota tion s

500

1000

1500

2000

2500

Grain Yields (kg ha-1)

Cow- So r g

Grou-Sorg

Sorg-Sorg

Cr op Rota tion s

500

1000

1500

2000

2500

Grain Yields (kg ha-1)

Figure 3. Effect of monocropping of sorghum and rotations with legumes (groundnut-sorghum and cow-

pea-sorghum) on sorghum grain yields during four years (2001-2004). Cow-Sorg = cowpea-sorghum; Grou-Sorg =

groundnut-sorghum; Sorg -Sorg = sorghum-sorghum.

Ye ar 2001

Year 2002

Ye ar 2003

Ye ar 2004

Grain yields (kg ha

–

Grain yields (kg ha

–

Grain yields (kg ha

–

Grain yields (kg ha

–

Grain yields (kg ha

–

54 V. Bado et al. / Agricultural Sciences 2 (2011) 49-55

An interaction was only observed between years and

rotation. The distribution of rainfall seemed to be more

important than the quantity of water received during the

season. For example, the highest grain yields were ob-

tained in 2001 and 2002 when there was good distribu-

tion of rains, particularly in September and August, even

though the total rainfall was lowest of the five years of

the experiment.

Mono cropping of sorghum produced the lowest

yields during the four years, and rotation of sorghum

with legumes increased sorghum yields by from 50% to

300% compared to monocropping (Figure 3). The ef-

fects of legumes were particularly noticeable during the

first year of rotation (2001). Sorghum grain yields in-

creased from 0.9 tonnes ha–1 in monocropping of sor-

ghum to 1.7 and 2.0 tonnes ha–1 when sorghum was ro-

tated with groundnut and cowpea, respectively. Except

for one year (2002), sorghum yields were higher in

cowpea-sorghum than a groundnut-sorghum rotation.

4. DISCUSSIO N

The two legumes increased soil mineral N during the

first weeks of the cropping season. Legume residues

provided more organic N, a source of mineral N for the

succeeding crop [12]. Despite the exportation of legume

shoots, the remaining crop residues and the below

ground part of legumes can improve organic matter of

the topsoil. Compared to sorghum, the residues of leg-

umes are of better quality. As shown by soil mineral N,

they better contributed to supplying more N in leg-

ume-sorghum rotations. Giller et al. [13] estimated that

15% to 20% of the nitrogen of legumes is recycled for

the succeeding crop by legume residues. The positive

interaction between organic and mineral N can justify

the effecti veness of legume on N upt ake by sorghum.

Our data confirmed the differences between the two

legumes on soil and roots infestation by nematodes. As

observed by other studies, cowpea increased nematode

infestation [14], while groundnut decreased the popula-

tion of nematodes [3,15,16]. The biological effects of

legumes are complex [17] but our results showed that

the N-effect seemed to be the most important factor

governing sorghum response to crop rotation. Nitrogen

and P are known to be the most limiting factors of Al-

fisols and Ultisols of West Africa [1,5]. Legumes can

also improve other soil properties such aspH of acid

soils, microbial N and fungal biomass in the rhizosphere

[17]. In the sensitive rainfed ecosystem of West Africa,

the mineral N supplied by legume residues at the start of

the season as a basal source of N can explain the good

development and yields of sorghum. The good soil con-

ditions created by legume residues such as cowpea can

assist the development of nematodes. The infestation by

nematodes was lowest in a groundnut-sorghum rotation,

probably because groundnut is not a favourable host for

nematodes of sorghum [3]. Despite high infestation

(cowpea) or reduction in nematode population (ground-

nut), nematodes didn’t affect sorghum yields and no re-

lationship was observed between sorghum yields and

nematode densities in soil or sorghum roots. The better

growth of sorghum in legume-sorghum rotations domi-

nated or limited the effects of nematodes. The quantity

and quality (organic N) supplied by the residues of leg-

umes improve soil N, biological properties and avail-

ability of other nutrients, leading to better growth and

good health for the succeeding sorghum. As reported

inprevious work, subsequent cereal yields are usually

increased in legume-cereal rotations [3,4,18] as a con-

sequence of mineral N provided by mineralization of

legume residues [19-22] and the improvement of soil

biological properties and availability of nutrients [17].

Then, despite the increase of the population of nema-

todes, the succeeding sorghum benefits from good nu-

triational conditions and has quicker and better growth,

particularly during the first period of the season. Other-

wise, the highest yields in cowpea-sorghum rotations

explained the predominance of N-effect on the negative

effects of parasitic nematodes.

5. CONCLUSIONS

Compared to the monocropping of sorghum, the two

legumes (cowpea and groundnut) increased N uptake by

succeeding sorghum as a consequence of organic N sup-

plied by legume residues (fallen senescent leaves and

below ground parts). Groundnut remains the most effec-

tive legume for reducing nematode infestation. Cowpea,

on the other hand, increased nematode infestation, but

because of the predominance of the N-effect of legume

residues and the improvement in physical, chemical and

biological conditions of the soil by legume residues,

nematode infestation did not affect the productivity of

the succeeding sorghum.

6. ACKNOWLEDGEMENTS

This study was partly funded by the International Atomic Energy

Agency (IAEA) under IAEA Contract BKF-10952. This research was

conducted as part of FAO/IAEA Coordinated Research Project on

Tropical Acid Soils. The authors are grateful to IAEA, FAO/IAEA

division and Dr. F. Zapata, Project Officer for his assistance.

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