Influence of phosphorus on the performance of cowpea (Vigna unguiculata (L) Walp.) varieties in the Sudan savanna of Nigeria

doi:10.4236/as.2011.23042

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Vol.2, No.3, 313-317 (2011)

doi:10.4236/as.2011.23042

Agricultural Scienc es

Influence of phosphorus on the performance of cowpea

(Vigna unguiculata (L) Walp.) varieties in the Sudan

savanna of Nigeria

A. Singh1*, A. L. Baoule1, H. G. Ahmed1, A. U. Dikko2, U. Aliyu1, M. B. Sokoto1, J. Alhassan1, M.

Musa1, B. Haliru1

1Department of Crop Science, Usmanu Danfodiyo University, Sokoto, Nigeria; *Corresponding author: [email protected],

[email protected]

2Department of Soil Science and Agricultural Engineering, Usmanu Danfodiyo University, Sokoto, Nigeria.

Received 28 March 2011; revised 24 May 2011; accepted 21 July 2011.

ABSTRACT

Savanna regions of Nigeria are deficient in ni-

trogen and phosphorus, which retard the

growth and yield of crops. Therefore, a study

was conducted in the wet season of 2006 at the

Dry Land Teaching and Research Farm of Us-

manu Danfodiyo University, Sokoto to evaluate

the effect of phosphorus on the growth and

yield of two cowpea varieties sourced from

Republic of Niger. Treatment consisted of four

(4) rates of phosphorus (0, 20, 40, 60 kg·ha–1)

factorialy combined with (2) varieties of cowpea

(KVX303096G and TN5-78) and laid out in a

randomized complete block design (RCBD) rep-

licated three (3) times. Results showed signifi-

cant response to applied P on pods per plant,

grain and stover yield and 100-seed weight with

highest respon se to the application of 60 kg P ha–1.

From this study it can be concluded that

KVX303096G and TN5-78 could both be sown

under Sokoto condition to obtain reasonable

yield of about 1 t·ha–1 of grain and 1.6 t·ha–1 of

stover. Irrespective of the varieties, application

of 60 kg P2O5 ha–1 could be recommended for

higher yi eld of co wpea (1.4 t·ha–1) rela tive to 0 kg

P/ha that yielded 1.0 t·ha–1.

Keywords: Cowpea [Vigna Ung uiculata (L.) Walp.];

Phosphorus; Sudan Savanna; Nigeria

1. INTRODUCTION

Cowpea (Vigna unguiculata (L.) Walp.) is an important

grain legume in the dry savanna of the tropics covering

12.5 million hectares with annual production of about

3.3 million tones [1]. Nigeria is the world’s largest

producer with 2.1 million tones followed by Niger with

650,000 tones and Mali with 110,000 tones [2]. About

64% of the area under cowpea is grown in central and

east Africa. Cowpea is mostly cultivated in mixture with

others crops such as millet and sorghum mostly in

Sahelian and Sudan region.

Cowpea is well adapted to poor fertility and low

rainfall conditions. Cowpea grows best on fertile, loam

soils with rainfall of 760 - 1520 mm during the growing

period, and thrives best on dry areas of Northern part of

Nigeria and transported to the Southern part of Nigeria

[3]. Cowpea is an important crop because of its role in

human and livestock nutrition. It reduces the shortage of

food by making efficient use of water and nutrient. It is a

source of protein and also less expensive than meat.

Cowpea is of vital importance to the livelihood of

several million of people in east and central Africa [4].

Cowpea is an important legume crop in the dry savannas

of Africa, especially West Africa. Out of the 12.5 million

hectare cultivated to cowpea worldwide, Singh et al. [5]

estimated that eight million hectare are in West and Cen-

tral Africa, distributed predominantly between Nigeria

and Niger. In spite of the fact that grain yields are low,

cowpea has continued to be a popular crop among

farmers. This is because cowpea provides high protein

food for people, especially children; it improves and

sustains soil fertility, and provides high quality fodder

for livestock [6,7]. Cowpea contributes to the improve-

ment of soil fertility by the fixation of nitrogen (N) in

the soil (60 - 70 kg·N·ha–1 to the subsequent crop) [8].

The result obtained from a research work carried by IITA

[9] showed that cowpea fixed 240 kg·ha–1 of N. The crop

provides a high proportion of its own requirement,

besides leaving a fixed N deposit in the soil of up to 60 -

70 kg·ha–1. In addition to its role-played in mixture with

cereals, the crop is advantageous in terms of weed

A. Singh et al. / Agricultural Science 2 (2011) 313-317

314

control, soil cover, protection from soil erosion and

dispersal of insects [10].

Phosphorus (P) is among the most needed elements

for crop production in many tropical soils. However,

many tropical soils are P-deficient [11]. Phosphorus,

although not required in large quantities, is critical to

cowpea yield because of its multiple effects on nutrition

[12]. All growing plants require P for growth and

development in significantly large quantity. P deficiency

is the most limiting soil fertility factor for cowpea

production [10]. Phosphorus although not required in

large quantities is critical to cowpea yield (particularly

for improved photoperiod-insensitive cultivars) because

of its multiples effects on nutrition. It not only increases

seed yields but also nodulation. Others workers have

reported that phosphorus application influences the

content of others nutrients in leaves [13] and seed. The

deficiency can be so acute in some soils of the savanna

zone of western Africa that plant growth ceases as soon

as the P stored in the seed is exhausted [14]. Because of

its multiple effects on plant nutrition (not only on

nodulation), a phosphorus fertilizer is recommended to

increase yields (P2O5: 20 - 60 kg·ha–1) [10]. Smyth and

Cravo [15] working on Xanthic Hapludox near Manaus,

Brazil reported that for cowpea critical levels for soil P

was 60 kg·P·ha–1.

Despite the importance of cowpea in human diet and

feed for animals, the yield obtained by most farmers is

very low. In Nigeria the average yield per hectare in the

respective years were 0.75 t·ha–1 in 1990, 0.72 t·ha–1 in

1991, 0.51 t·ha–1 in 1992, 1993 and 1994, 0.49 t·ha–1 in

1995, 0.45 t·ha–1 in 1996, 0.48 t·ha–1 in 1997, 0.41 t·ha–1

in 1998, 0.42 t·ha–1 in 1999, 2000, 2001 and 2002; 0.43

t·ha–1 2003 and 2004 [16]. Because of the rapid increase

in population, there is a high demand for food and

therefore, there is a need to augment the production of

cowpea. N is not critical for legumes because legumes

fix atmospheric N2 through symbiotic association with

strains of Rhizobium sp. Phosphorus is the second most

important nutrient after N and could be used to increase

production of cowpea as most soils in the tropics are P

deficient. Phosphorus is known to increases the yield of

cowpea by increased N2 fixation through nodulation and

utilization of N fertilizer [10]. Thus, this study was con-

ducted to evaluate the effect of phosphorus fertilizer on

yield of cowpea and select cowpea variety responsive to

phosphorus application.

2. MATERIALS AND METHODS

The experiment was conducted in 2006 cropping

season at the dry land farm of Usmanu Danfodiyo

University, Sokoto. Sokoto is located on latitude 13˚01′

N and at longitude 05˚15′ E and lies at an altitude of 350

m above the sea level. It falls in Sudan Savanna agro-

ecological zone. The rainfall starts mostly in June and

ends in October with a mean annual rainfall of about 350

- 700 mm. The maximum and minimum temperature of

Sokoto ranges from 40 to 15˚C, respectively [17]. The

treatments consisted of factorial combinations of four (4)

levels of phosphorous (0, 20, 40 and 60) and twovarieties

of cowpea (KVX303096G and T5-78) (8 treatment

combinations) laid out in a randomized complete block

design (RCBD) replicated 3 times.

The seeds of cowpea varieties were obtained from the

research institute of Niger Republic known as INRAN in

Tahoua State and sown on the 18th of June, 2006. Two

seeds were sown per hill at a depth of 3 - 4 cm and 75

cm apart at a plant-to-plant spacing of 50 cm within a

row. Urea at the rate 15 kg·ha–1 was applied as a starter

dose to all the plots while P2O5 was applied as per

treatment (0, 20, 40, and 60 kg P2O5 ha–1). Weeding was

carried out twice manually at 5 and 8 weeks after sowing.

The plots were sprayed with karate (Lambda cyhorlothrim)

to take care of Aphis craccivora. Harvesting was done

manually at physiological maturity when the pods had

turned yellowish brown.

Data collected on yield parameters were subjected to

analysis of variance (ANOVA) technique using Statisti-

cal Analysis System (SAS) [18]. Significant different

between treatments were further analyzed using least

significant different test (LSD) for mean separation.

3. RESULTS AND DISCUSSION

3.1. Physico-Chemical Prope rties of the So il

The general chemical and physical properties of the

surface soils (0 - 15 cm) used for the field experiments

are presented in Tabl e 1 . Soils at the experimental site

were largely Sandy and the soil pH (H2O) was moder-

ately acidic (6.5). The organic carbon (OC), total N and

available P in the soil was very low while exchangeable

K in the soil at the experimental site was low. The total

annual rainfall at the experimental site was 604 mm with

peak in August. The rain established in June and ceased

in October coinciding with sowing and harvesting of

cowpea, respectively (Figure 1).

Ta bl e 1 . Physico-chemical characteristic of the soil at the ex-

periment site.

Parameters Value Remarks

Texture Sandy

pH in water 6.50 Mod. acidic

pH in CaCl2 6.19

Total phosphorus (P) (mg·kg–1) 1.80 Very Low

Organic carbon (g·kg–1) 1.58 Very Low

Total nitrogen (N) (g·kg–1) 0.65 Very low

Exchangeable potassium (K) (cmol·kg–-1) 0.65 Low

A. Singh et al. / Agricultural Science 2 (2011) 313-317

315315

Figure 1. Monthly rainfall pattern and total annual

rainfall at the Experimental site. (Source: Energy Re-

search Center, Usmanu Danfodiyo University, Soko-

to).

Table 2. Effect of variety and phosphorus on the number of

pods per plant and seeds per pod.

Treatment Pods per plant Seeds per pod

Variety (V)

KVX303096G 52 ± 6.8 9.7 ± 2.8

TN5-78 49 ± 8.4 10.8 ± 3.8

SE 2.1 0.51

Significance level ns ns

Phosphorus (P)

0 43 ± 8.3b 11.1 ± 1.8

20 50 ± 7.8ab 9.9 ± 1.2

40 54 ± 3.4a 10.3 ± 2.4

60 54 ± 3.2a 9.7 ± 1.8

SE 2.9 0.73

Significance level s ns

Interaction

V × P ns ns

3.2. Number of Pods per Plant and Seeds

per Pod

There was no significant effect of the variety on the

number of pods per plant. However, variety KVX303096

G recorded higher number of pods per plant (52) than

the variety TN5-78 (49) (Table 2). Phosphorus had

significant (P < 0.05) effect on the number of pods per

plant. Significantly (P < 0.05) higher pods per plant

were recorded in plots applied with 40 (54) and 60 (54)

kg P ha–1 than 0 (43) and 20 (50) kg P ha–1 (Tab le 2).

This could be due to higher level of P in those plots.

Mokwunye and Bationo [19] have reported that, P is

essential for photosynthesis, pod development and grain

filling in leguminous crops. P is responsible for nodu-

lation in cowpea. Thus higher nodulation resulted in

higher nitrogen fixation and eventually the number of

pods per plant. There was no significant effect of

interaction of variety and phosphorus on pods per plant.

The results of the present study are higher than that

recorded by Okeleye et al. [20] where the number of

pods per plants obtained ranged from 7.3 to 30.8 by ap-

plying a rate of 20 and 30 kg P ha–1 using short and me-

dium duration cowpea varieties.

Both the variety and phosphorus had no significant

effect on the number of seeds per pod. Statistically simi-

lar seed number per pod was recorded in variety TN5-78

(10.8) and KVX303096G(9.7). Interaction between vari-

ety and phosphorus had no significant effect on the num-

ber of seeds per pod.

3.3. Grain and Stover Yield

There was significant effect of phosphorus on the

stover yield of cowpea. Similar to the grain yield, sig-

nificantly (P < 0.05) higher stover yield was recorded in

plots supplied with 60 (2115 kg·ha–1) than with 0 (1411

kg·ha–1), 20 (1482 kg·ha-1) and 40 kg P2O5 ha–1 (1571

kg·ha–1). This could again be attributed to the availability

of P that would have increased the intensity of nodula-

tion and thus nitrogen fixation. Higher nitrogen fixation

would result in higher yield of the crop. Interaction be-

tween phosphorus and variety had no significant effect

on the stover yield of cowpea.

Variety had no significant effect on the grain yield of

cowpea. Statistically similar grain yield was recorded in

both KVX303096G (1120 kg·ha–1) and TN5-78 (1074

kg·ha–1) (Table 3). This indicated the similar performance

of the two varieties under Sokoto agro-ecology.

There was significant (P < 0.05) response to applied P

on the grain yield of cowpea. Significantly higher grain

yield was recorded in plots applied to 60 (1353 kg·ha–1)

than 0 (1017 kg·ha–1), 20 (1067 kg·ha–1) and 40 kg P ha–1

(951 kg·ha–1). Application of 20 and 40 kg P2O5 ha–1 was

Ta b le 3 . Effect of variety, phosphorus and their interaction on

the grain and stover yield of cowpea.

Va ri e ty P levels

(kg·ha–1)KVX303096GTN5-78

Mean phosphorus

levels (Main effect P)

Grain yield (kg·ha-1)

0 928 ± 239 b 1106 ± 188 ab 1017±216 b

20 1165 ± 179 ab968 ± 218 b 1067±209 b

40 914 ± 82 b 988 ± 298 b 951±200 b

60 1472 ± 266 a 1235 ± 61 a 1353±216 a

Means

Va ri e ty 1120 ± 294 1074 ± 211

SE SEVa ri e ty = 62.6; SEphosphorus = 88.6;

SEVariety × Phosphorus = 125.28

Stover yield (kg·ha–1)

0 1314 ± 261 1509 ± 522 1411 ± 384 b

20 1753 ± 665 1546 ± 202 1649 ± 454 ab

40 1595 ± 416 1881 ± 539 1738 ± 458 ab

60 2072 ± 265 2158 ± 284 2115 ± 250 a

Means

Va ri e ty 1684 ± 468 1773 ± 449

SE SEVa ri e ty = 100.1; SEphosphorus = 141.5;

SEVariety × Phosphorus = 259.9

Values following ± are standard deviation of the means. Means in a column

for Phosphorus and across row and column for variety x P interaction fol-

lowed by same letter (s) are not significantly different at 5% level, ns = Not

significant, *Significant at 5% level.

A. Singh et al. / Agricultural Science 2 (2011) 313-317

316

not different from those plots that were not applied with

P (0 kg P ha–1). This indicated that P became a limiting

factor at later stage of plant growth. Higher yield re-

corded with 60 kg·ha–1 was attributed to higher avai-

lability of P that is responsible for effective nodulation

in cowpea. Okeleye and Okelana [21] also observed sig-

nificantly increased nodulation, grain yield, and total dry

matter for cowpea varieties in response to P application.

Variety had no significant effect on the stover yield of

cowpea as both varieties recorded 1600 kg·ha–1 of cow-

pea stover (Table 3).

There was significant effect of phosphorus on the

stover yield of cowpea. Similar to the grain yield,

significantly (P < 0.05) higher stover yield was recorded

in plots supplied with 60 (2115 kg·ha–1) than with 0

(1411 kg·ha–1), 20 (1482 kg·ha–1) and 40 kg P2O5 ha–1

(1571 kg·ha–1). This could again be attributed to the

availability of P that would have increased the intensity

of nodulation and thus nitrogen fixation. Higher nitrogen

fixation would result in higher yield of the crop. In-

teraction between phosphorus and variety had no sig-

nificant effect on the stover yield of cowpea.

3.4. Harvest Index and 100-Seed Weight

Harvest index is the proportion of grain in the total

aboveground biomass of the crop expressed in percent-

age and it ranged from 36% to 40%. This indicated that

only 36% to 40% of the photosynthate was translocated

to the grain. Variety did not have significant influence on

the HI of the crop. KVX303096G recorded statistically

(P > 0.05) similar HI with TN5-78 variety (Ta b le 4). P

also did not have significant influence on the HI of the

crop implying that HI is a genetic trait and will only be

influenced by variety differences. Effect of interaction

between variety and phosphorus was not significant

(Table 4).

There was no significant effect of variety on the hun-

dred seeds weight (Figure 2). The two varieties recorded

similar 100-seed weight of about 20.2 g. Effect of phos-

phorus on 100-seed weight was significant (P < 0.05)

Table 4. Effect of variety, phosphorus and their interaction on

harvest index of cowpea.

Harvest index (%) P levels

(kg·ha–1) KVX303096G TN5-78

Mean phosphor-

rus levels

0 41.2 ± 1.8 43.0 ± 6.6 42 ± 4.4

20 40.9 ± 6.4 38.4 ± 6.9 40 ± 6.1

40 37.0 ± 5.7 35.2 ±13.7 36 ± 9.4

60 41.4 ± 1.4 36.6 ± 3.7 39 ± 3.7

Means Variety 40.0 ± 4.2 38.0 ± 7.9

SE SEVa r ie t y = 2.10; SEphosphorus = 2.97;

SEVariety × Phosphorus = 4.196

Values following ± are standard deviation of the means.

Figure 2. Main effect of variety on 100-seed weight of

cowpea.

Figure 3. Main effect of phosphorus levels on 100-

seed weight of cowpea. Bars with same letter (s) are

not significantly different using LSD at 5% level.

Table 5. Interaction effect of variety x phosphorus on 100-

grain weight of cowpea.

100-grain weight (g) Phosphorus levels

(kg·ha-1) KVX303096G TN5-78

0 18.32 ± 0.06 b 18.59 ± 0.54 b

20 20.51 ± 1.05 a 20.60 ± 0.23 a

40 21.50 ± 0.57 a 20.54 ± 0.93 a

60 20.30 ± 0.73 a 20.98 ± 1.31 a

SE 0.439

Values following ± are standard deviation of the means. Means across rows

and columns followed by same letter (s) are not significantly different using

LSD at 5% level.

with 40 kg·ha–1 (54.17 g) and 60 kg·ha–1 (54.17 g)

recording significantly higher 100-seed weight than 0 kg

P ha–1 (42.83 g) (Figure 3). The interaction of variety

and phosphorus on 100-grain weight of cowpea was

significant (Table 5). For both variety KVX303096G and

TN5-78, application of 20, 40 and 60 kg P ha–1 resulted

in similar 100-grain weight (Table 5). For all levels of P

including control, the two varieties were at par. These

results coincide with the results recorded by Okeleye et

al. [20] where the weight of 100 seed of cowpea ranged

A. Singh et al. / Agricultural Science 2 (2011) 313-317

317317

from 13.50 to 39.7 g by the application of 20 and 30 kg

P ha–1. Phosphorus intervenes in the formation of seed

and improves seed quality [21].

Openly accessible at

4. CONCLUSIONS

From this study it can be concluded that KVX303096G

and TN5-78 could both be sown under Sokoto condition

to obtain reasonable yield of about 1 t·ha–1 of grain and

1.6 t·ha–1 of stover. Irrespective of the varieties, applica-

tion of 60 kg P2O5 ha–1 could be recommended for higher

yield of cowpea (1.4 t·ha–1) relative to 0 kg P2O5 ha–1

that yielded 1.0 t·ha–1. However, 60 kg P2O5 ha–1 may not

be the optimum as further application of P may or may

not increase the yield of cowpea. Therefore it is subject

to investigation.

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