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African Crop Science Journal
African Crop Science Society
ISSN: 1021-9730 EISSN: 2072-6589
Vol. 8, Num. 1, 2000
African Crop Science Journal, Vol

African Crop Science Journal, Vol. 8. No. 1, pp. 49-62, 2000

PERFORMANCE OF POGEONPEA AND ITS FINGER MILLET AND SORGHUM INTERCROPS

P.R. Rubaihayo, D.S.O Osiru and P. Okware

Department of Crop Science, Makerere University, P.O. Box 7062, Kampala, Uganda

Code Number: CS00005

ABSTRACT

Field trials were conducted to determine the optimum plant population and spatial arrangement of finger millet/pigeonpea and sorghum/pigeonpea intercropping systems, identify the intercrop compatibility of finger millet and sorghum with short- and medium-duration pigeonpea, and evaluate insecticide application strategies for the control of pod borers, pod sucking bugs and podfly on pigeonpea. The experiments were conducted at Makerere University Agricultural Research Institute Kabanyolo (MUARIK) and Ngetta experimental station during the second rains season of 1997 and first rains season of 1998. Theoretical planting densities (2.1, 2.8, 4.2, 4.8, 5.6, 8.3, 11.1, and 16.7 plants m-2 ) for pigeonpea, (8.3, 11.1, 16.7, and 33.3 plants m-2 ) for finger millet and 5.6 plants m-2 for sorghum intercrops were studied using KAT 60/8, ICPL 87091 and ICP 6927 pigeonpea varieties, Pese 1 finger millet variety and Seredo sorghum variety. Spraying against major pigeonpea insect pests was carried out at vegetative stage, vegetative to pod maturity, flower bud initiation to pod formation, and pod formation to pod maturity. In the pigeonpea/finger millet intercrop system, optimal combinations in terms of higher land equivalent ratio (LER) values were given by 16.7 plants m-2 of ICPL 87091 and 8.3 plants m-2 of Pese 1, 4.2 plants m-2 of KAT 60/8 and 33.3 plants m-2 of Pese 1. Planting of pigeonpea and finger millet or pigeonpea and sorghum in a 2:2 row arrangement gave higher total LER values than in the other arrangements and thus, was found to be an optimal row arrangement. Spraying pigeonpea cultivars ICPL 87091 and KAT 60/8 against major insect pests at flower bud initiation to pod formation and at pod formation to pod maturity, respectively, produced significantly (P<0.05) better yields than unsprayed and was more cost effective than the other spraying regimes.

Key Words: Cajanus cajan, insect pest management, intercropping, plant density, spatial arrangement, sole cropping, yield advantage

RÉSUMÉ

Des essais ont été conduit pour détérminer la densité optimale de population de plantes et l’arrangement spacial des systèms d’association et d’eleusine/pois d’embrare et du sorgho/pois d’embrare, identifier la compatibilité de l’association du eleusin le sorgho avec le pois d’embrave de courte et moyenne durée et évaluer de stratégies d’application d’insecticides pour le contr™le des boreurs de gousses, pucerons suceurs de gousses et des podfly sur le pois d’embrave. Les experiences ont été conduites à l’Institut agricole Kabanyoro de l’Université de Makerere (MUARIK) et à la station experimentale de Ngetta pendant la seconde saison de 1997 et dans al premier saison de plue de 1998. La densité de plantation théoriques (2.1, 2.8, 4.2, 4.8, 5.6, 8.3, 11.1, et 16.7 plants par m-2 ) pour le pois d’embrave, (8.3 11.1, 16.7 et 33.3 plants par m-2 ) pour l"eleusine et 5.6 plants m-2 de sorgho en association ont été étudiées utilisant les variétés KAT 60/8, ICPL 87091 et ICP 6927 de pois d’embrare, Pese 1 d’eleusine et de la variété Seredo du sorgho. Le traitment contre les principaux pests du pois d’embrave a été fait au stade végétatif, du stade régétatif à la maturité de gousses, de l’initition de la floraison à la formation de gousses, et de la formation de gousse à la maturité de gousses. Dans le système d’association pois d’embrave et l’eleusine, les combinaisons optimales en termes du rapport equivalent de la terre (LER) les plus élevées ont été données par la densité de 16.7 plantes m-2 pour la variété ICPL 87091 et 8.3 plants m-2 pour Pese 1 et 4.2 plants m-2 pour KAT 60/8 et 33.3 plantes m-2 pour Pese 1. La plantation du pois d’embrave avec l’eleusine ou pois d’embrave avec sorgho dans un arrangement en lignes 2 à 2 a donné le rapports totale LER le plus élevé plus que d’autre arrangements, et il a été Arouvé comme arrangement optimal en lignes. La pulverisation des cultivars ICPL 87091 et KAT 60/8 de pois d’embrave contre les pestes de l’initiation à la formation de gousses et de la formation de gouses à la maturité ont produit significativement de bons rendements plus que les traitements non pulverisés et était plus rentable que d’autres régimes d’application.

Mots Clés: Pois cajan, gestion d’insecte nuisible, association, densité des plantes, arrangement spatial, culture en pure, avantage de rendement

INTRODUCTION

Pigeonpea (Cajanus cajan L. Millsp.) is grown in the drier areas of Uganda with mean annual rainfall ranging from 768-1115 mm in the north-east and north, and 1065-1670 mm in the wetter areas of the north-west of the country. Pigeonpea as a grain legume forms an important part of the diet in these regions (Acland, 1986).

The main pigeonpea cultivars in the country are landraces which take 6-10 months to mature. The crop is judiciously intercropped with finger millet (Eleusine corocana L. Gaertn.) and sorghum (Sorghum bicolor L. Moench) (Silim et al., 1994). In traditional cropping system, actual pigeonpea yields on-farm are very low, 0.3-0.6 t ha-1. However, in experimental situations grain yields as high as 1.4 t ha-1 have been achieved (Obuo et al., 1996). Low yields obtained at the farm level are attributed to numerous constraints, particularly poor mana-gement of the intercropping systems with respect to plant population, spatial arrangement, unimproved cultivars, and the heavy insect damage.

Higher yields from crops associated with pigeonpea in paired-row sowings have been reported by Umrani et al. (1987) and Ali (1990) who found that this system allowed more radiation to reach short component crops grown between the tall crop rows and minimised competition for light. The current improved pigeonpea cultivars including ICPL 87091, KAT 60/8 and ICP 6927 are shorter than the landraces and mature in 3-5 months. The cultivars have demonstrated a potential to replace the landraces. Obuo et al. (1996) reported that sole ICPL 87091 cultivar required plant spacing of 60 x 20 cm (8.3 plants m-2 ) and KAT 60/8 required 60 x 30 cm (5.5 plants m-2 ) for maximum grain yield. Knowledge on the performance of these varieties under intercropping systems is, however, lacking.

Pod damage by insect pests can greatly reduce crop yield, particularly since pigeonpea potential to compensate for pod damage is limited (Reed and Lateef, 1990). Minja (1996) identified pod borers, pod sucking bugs and podfly as the most important pod damaging insect pests limiting pigeonpea production. Reed and Lateef (1990) observed that pod borer damage in pigeonpea starts when the larvae bore into buds, flowers and developing pods, and the large nymphs and adult pod sucking bugs suck the developing seed through pod walls. Reed et al. (1989) reported that the podfly larvae feed on developing seed. Control of pigeonpea pod borers, pod sucking bugs and podfly has been mostly through use of chemical insecticides based on recommended application regimes and on calendar intervals. However, Reed and Lateef (1990) suggested a regime based on plant growth stages to provide better synchrony of pesticide application with pest attack.

This study was conducted to determine the optimum plant population and plant row arrangement of finger millet/pigeonpea and sorghum/pigeonpea systems, and evaluate insecticide application strategies using Reed and Lateef (1990) suggested regime for the control of pod borers, pod sucking bugs and podfly on pigeonpea.

Materials and methods

The experiments were carried out at Makerere University Agricultural Research Institute, Kabanyolo (MUARIK) and Ngetta experimental station. Three improved pigeonpea varieties ICPL 87091 (4 months duration), KAT 60/8 and ICP 6927 (5-6 months duration) were used in the study. Varieties ICPL 87091 and KAT 60/8 are among pigeonpea varieties that have been tested on-farm in Uganda and found to be acceptable to the farmers (Okurut-Akol et al., 1996). Finger millet (cv. Pese 1) and sorghum (cv. Seredo) were used as the component cereals. Crops were thinned to the desired populations within 2 weeks after emergence. Fields were weeded two to three times by hand. The crops were protected against pest attack by spray application of Nurelle-D [a mixture of cypermethrin (600 g l-1) and dimethoate (200 g l-1)] at two weeks interval starting four weeks after planting to maturity. The experiments were in a split plot design with sub-plot sizes of 3 x 8.4 m at Kabanyolo and 6 x 5 m at Ngetta replicated three times.

Experiment 1. The effect of plant population (intra-row spacing) on yield of pigeonpea and finger millet component crops was investigated using single alternating rows (1:1) in the second rains of 1997 (October-December) at MUARIK and in the first rains of 1998 (March - July) at Ngetta. The pigeonpea/cereal intercrops formed the main plots and the intra-row spacing of the component crops formed the sub-plots. Similar treatments were accorded to the sole crops. The treatments are given in Table 1.

Table1. Treatments used in the plant population experiment in MUARIK and Ngetta

Cropping system

Pigeonpea

Finger millet

Spacing (cm)

Plant density m-2

Spacing (cm)

Plant density m-2

KAT 60/8 + Pese 1

60 x 20

8.3

60 x 20

8.3

KAT 60/8 + Pese 1

60 x 30

5.6

60 x 15

11.1

KAT 60/8 + Pese 1

60 x 35

4.8

60 x 10

16.7

KAT 60/8 + Pese 1

60 x 40

4.2

60 x 5

33.3

ICPL 87091 + Pese 1

60 x 10

16.7

60 x 20

8.3

ICPL 87091 + Pese 1

60 x 15

11.1

60 x 15

11.1

ICPL 87091 + Pese 1

60 x 20

8.3

60 x 10

16.7

ICPL 87091 + Pese 1

60 x 30

5.6

60 x 5

33.3

KAT 60/8 sole

60 x 30

5.6

-

-

ICPL 87091 sole

60 x 20

8.3

-

-

Pese 1 sole

-

-

30 x 10

33.3

Experiment 2. The effects of plant row arrangement on yield of pigeonpea/sorghum and pigeonpea/millet component crops were investigated using pigeonpea varieties KAT 60/8, ICP 6927 and ICPL 87091, and Seredo sorghum and Pese 1 finger millet. The intercrops of pigeonpea were laid out in the main plots and the plant row arrangement in the sub-plots. In August 1997, KAT 60/8, ICP 6927 and ICPL 87091 and Seredo were planted at MUARIK under the row arrangements given in Table 2. In April 1998, however, only KAT 60/8 and ICPL 87091 were planted with Pese 1 and Seredo in the combinations shown in Table 3.

Table 2. Treatments used in the plant row arrangement experiment during the second season of 1997 at MUARIK

Cropping system

Row arrangement

Pigeonpea

Sorghum

Spacing (cm)

Plant density m-2

Spacing (cm)

Plant density m-2

KAT 60/8 + Seredo

1:1

120 x 30

2.8

120 x 15

5.6

KAT 60/8 + Seredo

1:2

180 x 30

2.8

180 x 15

5.6

KAT 60/8 + Seredo

2:2

240 x 30

2.8

240 x 15

5.6

ICPL 87091 + Seredo

1:1

180 x 20

4.2

120 x 15

5.6

ICPL 87091 + Seredo

1:2

180 x 20

4.2

180 x 15

5.6

ICPL 87091 + Seredo

2:2

240 x 20

4.2

240 x 15

5.6

ICP 6927 + Seredo

1:1

120 x 40

2.1

120 x 15

5.6

ICP 6927 + Seredo

1:2

180 x 40

2.1

180 x 15

5.6

ICP 6927 + Seredo

2:2

240 x 40

2.1

240 x 15

5.6

KAT 60/8 sole

-

60 x 30

5.6

-

-

ICPL 87091 sole

-

60 x 20

8.3

-

-

ICP 6927 sole

-

60 x 40

4.2

-

-

Seredo sole

-

-

-

60 x 20

8.3

TABLE 3. Treatments used in the plant row arrangement experiment during the first rains season of 1998 at MUARIK

Cropping system

Row arrangement

Pigeonpea

Finger millet

Sorghum

Spacing (cm)

Plant density (m-2 )

Spacing (cm)

Plant density (m-2 )

Spacing (cm)

Plant density (m-2 )

KAT 60/8 + Pese 1

1:1

120 x 15

5.6

120 x 5

16.7

-

-

KAT 60/8 + Pese 1

1:2

180 x 15

5.6

180 x 5

16.7

-

-

KAT 60/8 + Pese 1

2:2

240 x 15

5.6

240 x 5

16.7

-

-

ICPL 87091 + Pese 1

1:1

120 x 10

8.3

120 x 5

16.7

-

-

ICPL 87091 + Pese 1

1:2

180 x 10

8.3

180 x 5

16.7

-

-

ICPL 87091 + Pese 1

2:2

240 x 10

8.3

240 x 5

16.7

-

-

KAT 60/8 + Seredo

1:1

120 x 30

2.8

-

-

120 x 15

5.6

KAT 60/8 + Seredo

1:2

180 x 30

2.8

-

-

180 x 15

5.6

KAT 60/8 + Seredo

2:2

240 x 30

2.8

-

-

240 x 15

5.6

ICPL 87091 + Seredo

1:1

120 x 20

4.2

-

-

120 x 15

5.6

ICPL 87091 + Seredo

1:2

180 x 20

4.2

-

-

180 x 15

5.6

ICPL 87091 + Seredo

2:2

240 x 20

4.2

-

-

240 x 15

5.6

KAT 60/8 sole

-

60 x 30

5.6

-

-

-

-

ICPL 87091 sole

-

60 x 20

8.3

-

-

-

-

Pese 1 sole

-

-

-

30 x 10

33.3

-

-

Seredo sole

-

-

-

-

-

60 x 20

8.3

Experiment 3. Identification of appropriate stage of pigeonpea growth for insecticide application as an aid in reducing cost of spraying against pest damage on pigeonpea was carried out at Ngetta in 1998, to determine the critical stage of pigeonpea growth for economic spraying against pod borers, pod sucking bugs and podfly, by using two pigeonpea varieties ICPL 87091 and KAT 60/8 in sole plots. Pigeonpeas were protected with sprays of Nurelle-D at various stages of growth (Table 4). The first spray was applied two weeks after crop emergence and subsequent sprays were carried out at 7 day intervals to pod maturity. Damage was accessed on basis of pods bored and seeds sucked.

In all experiments, data collected were taken from a quadrant of size 4 m2 marked in the centre of each plot. The total grain weight obtained from the plant stand harvested quadrant was used to estimate yield m-2 and yield in kg ha-1. The data collected were subjected to analysis of variance using MstatC and the means separated using LSD tests at P=0.05. Land Equivalent Ratios (LERs) were computed as described by Willey (1979) and Mead and Willey (1980) to indicate the yield advantage of intercropping finger millet and sorghum with introduced pigeonpea varieties.

Table 4. Different stages of pigeonpea growth at which insecticide was applied at Ngetta

Spray regimes

Vegetative stage

Flower bud initiation

Pod formation

Pod maturity

1-0-0-0

1

0

0

0

1-1-1-1

1

1

1

1

0-1-1-0

0

1

1

0

0-0-1-1

0

0

1

1

0-0-0-0

0

0

0

0

0 = Unsprayed, 1 = Sprayed

RESULTS AND DISCUSSION

Pigeonpea plant height was significantly (P<0.05) influenced by intercropping (Tables 5 and 6). The mean plant height of KAT 60/8 intercrop varied from 100.7 to 129.1 cm during the second season of 1997 (Table 5) and from 115.4 to 135.0 cm during the first season of 1998 (Table 6). For ICPL 87091 intercrop, heights ranged from 71.0 to 76.4 cm (Table 5), which was non-significant, and from 82.0 to 94.9 cm (Table 6) where intercropping at a plant density of 16.7 plants m-2 and 8.3 plants m-2 caused significant (P<0.05) increase in ICPL 87091 plant height. Plant heights of KAT 60/8 or ICPL 87091 pigeonpea were shorter during the second season of 1997 than the first season of 1998. It was also noted that KAT 60/8 at a plant density of 4.2 plants m-2 in finger millet plant density of 33.3 plants m-2 had significantly (P<0.05) taller plants than the sole cropped KAT 60/8 during 1998 (Table 5).

Table 5. Means of yield and yield components of the component crops and mixtures during second rains season of 1997 at MUARIK

Component plant density m-2 (pigeonpea + intercrop)1

Yield components of pigeonpea

Yield (kg ha-1

Total LER

Plant height

Branches plant-1

Pods plant-1

Seeds pod-1

Pigeonpea

Finger millet

Combined

PP1+FM (8.3+8.3)

119.2

5.0

24.6

5.2

848

867

1715

1.18

PP1+FM (5.6+11.1)

100.7

5.9

30.2

5.0

785

989

1774

1.17

PP1+FM (4.8+16.7)

109.7

5.6

25.3

5.3

691

1100

1791

1.13

PP1+FM (4.2+33.3)

129.1

2.2

10.3

4.8

593

1300

1893

1.12

PP2+FM (16.7+8.3)

73.5

5.0

20.4

5.4

1417

933

2350

1.35

PP2+FM (11.1+11.1)

76.4

4.8

29.4

5.4

1100

944

2044

1.14

PP2+FM (8.3+16.7)

75.2

4.4

19.6

5.4

887

1067

1954

1.05

PP2+FM (5.6+33.3)

71.0

2.2

9.5

5.1

883

1650

2533

1.30

SolePP1 (5.6)

112.9

6.0

66.6

5.2

1044

1044

1.00

 

SolePP2 (8.3)

88.4

7.4

54.6

5.4

1481

1481

1.00

 

Sole FM (33.3)

-

-

-

-

-

2352

2352

1.00

LSD (0.05)

10.0

0.8

3.7

NS

111.2

72.8

159.3

-

C.V (%)

6.0

9.8

9.8

6.5

6.9

3.7

4.5

-

1Refer to Table 1;PP1 = KAT 60/8 (pigeonpea),PP2= ICPL 87091 (pigeonpea), and FM= PESE 1 (finger millet); NS= Not significant at P=0.05

Table 6. Means of yield and yield components of component crops and mixtures during 1998 at Ngetta

Component plant density m-2 (pigeonpea + intercrop)1

Yield components of pigeonpea

Yield (kg ha-1)

Plant height (cm)

Branches plant-1

Pods plant-1

Seeds pod-1

Pigeonpea

Finger millet

Combined

Total LER

PP1+FM (8.3+8.3)

115.4

3.9

35.9

5.3

1378

1472

2850

1.01

PP1+FM (5.6+11.1)

135.0

5.2

55.3

5.0

1098

1830

2928

0.99

PP1+FM (4.8+16.7)

127.1

4.8

41.2

4.8

789

2861

3650

1.14

PP1+FM (4.2+33.3)

132.7

4.7

48.4

5.2

709

3944

4655

1.40

PP2+FM (16.7+8.3)

94.9

4.4

33.5

5.4

2345

1325

3670

1.19

PP2+FM (11.1+11.1)

82.0

4.9

23.8

5.0

1645

1428

3073

0.97

PP2+FM (8.3+16.7)

82.7

4.4

25.9

5.2

926

2200

3126

0.93

PP2+FM (5.6+33.3)

88.8

3.9

25.2

5.4

850

3156

4006

1.17

SolePP1 (5.6)

136.0

5.0

92.0

5.3

2272

-

2272

1.00

SolePP2 (8.3)

103.3

5.4

53.5

5.4

2844

-

2844

1.00

Sole FM (33.3)

-

-

-

-

-

3622

3622

1.00

LSD (0.05)

21.53

NS

12.09

NS

235.0

238.9

159.3

-

C.V (%)

11.29

17.72

18.81

4.00

10.85

5.90

5.48

-

1Refer to Table 1;PP1 = KAT 60/8 (pigeonpea),PP2= ICPL 87091 (pigeonpea), and FM= Pese 1 (finger millet); NS= Not significant at P=0.05

The mean number of branches of KAT 60/8 were significantly (P<0.05) influenced by intercropping and varied from 2.2 to 5.9 (Table 5) and from 3.9 to 5.2 (Table 6). The number of branches of ICPL 87091 were significantly (P<0.05) influenced by intercropping with finger millet (Table 5). Similar results were observed during1998 (Table 6). The results indicated that intercropping had more influence on the number of branches of pigeonpea than locations and seasons. Treatments KAT 60/8 + Pese 1 and ICPL 87091 + Pese 1 with recommended sole-finger millet population of 33.3 plants m-2 in both seasons produced the lowest number of branches, indicating a high influence of cereal competition to the branching capacity of pigeonpea. This influence was translated into reduced number of pods per plant and finally yield per unit area.

The mean number of pods of KAT 60/8 was significantly (P<0.05) influenced by intercropping and ranged from 10.3 to 30.2 in 1997 (Table 5) and from 35.9 to 55.3 in 1998 (Table 6). Similar influence was observed for ICPL 87091 intercrop where pod numbers varied from 9.5 to 29.4 (Table 5) and from 23.8 to 33.5 (Table 6). The number of pods of KAT 60/8 was influenced by intra-row spacing during 1997 and 1998 but ICPL 87091 was only affected in 1997 (Table 5). The high number of pods for KAT 60/8 intercrop at a plant density of 5.6 plants m-2 was due to more branches formed, while for ICPL 87091 intercrop it was at a plant density of 11.1 plants m-2 (Table 5) and 16.7 plants m-2 (Table 6) thus the taller plants possibly gave the cultivar a better position for light interception and increased stimulation for pod formation leading to better yield. Obuo et al. (1996) reported that KAT 60/8 required 5.6 plants m-2 for maximum grain yield.

The mean number of seeds of both cultivars in the two seasons and locations was not significantly influenced by intercropping, indicating the stability of this character. However, the estimated yield per hectare of both cultivars showed significant (P<0.05) influence, of intercropping with finger millet between seasons and locations. Estimated higher yields per hectare were observed at the highest plant density of 8.3 plants m-2 for KAT 60/8 and at 16.7 plants m-2 for ICPL 87091 intercropped with finger millet at the lowest plant density of 8.3 plants m-2 . The lower yields were obtained at lowest plant density of 4.2 plants m-2 for KAT 60/8 and at 5.6 plants m-2 for ICPL 87091 intercropped with finger millet at the highest plant density of 33.3 plants m-2 due to increased competition from finger millet.

The estimated yield per hectare of finger millet was influenced by intercropping with both cultivars, seasons and locations (Tables 5 and 6). Higher yields per hectare of intercropped finger millet were obtained in treatments where KAT 60/8 or ICPL 87091 intercrops provided less competition due to lower plant populations per unit area. This is probably the reason why the farmers treat the pigeonpeas in the intercropping systems as a minor component crop.

The total land equivalent ratio (LER) values of finger millet intercropped with KAT 60/8 varied from 1.12 to 1.18 (Table 5) and from 0.99 to 1.40 (Table 6) while ICPL 87091 intercrop gave total LER values which varied from 1.05 to 1.35 (Table 5) and from 0.93 to 1.19 (Table 6). The second season of 1997 (Table 5), produced total LER values greater than 1 while total LER values of less than 1 were recorded in some intercrops in 1998, indicating no land-use yield advantage of intercropping in these combinations (Willey, 1979; Mead and Willey, 1980). In the 1997 season, the highest yield advantage (LER=1.35) was recorded where ICPL 87091 was planted at the closer intra-row spacing of 10 cm (16.7 plants m-2 ) with Pese 1 at the wider intra-row spacing of 20 cm (8.3 plants m-2 ). In the same season, KAT 60/8 /Pese1 intercrop planted at the same intra-row spacing of 20 cm gave the highest LER value of 1.18 in treatments involving KAT 60/8. Planting finger millet at plant density of 33.3 plants m-2 together with KAT 60/8 at 4.2 plants m-2 and ICPL 87091 at 5.6 plants m-2 gave significantly (P<0.05) higher estimated yield than from sole pigeonpea and/or sole finger millet (Table 5).

In the 1998 season, the highest yield advantage (LER=1.40) was from KAT 60/8 planted at the wider intra-row spacing of 40 cm (4.2 plants m-2 ) with Pese 1 at the closer intra-row spacing of 5 cm (33.3 plants m-2 ). Within the same season ICPL 87091 intercrop planted at the closer intra-row spacing of 10 cm (16.7 plants m-2 ) with finger millet at the wider intra-row spacing of 20 cm (8.3 plants m-2 ) gave the highest LER value of 1.19 in treatments involving KAT 60/8. For treatments involving ICPL 87091, the highest LER value of 1.17 was obtained when this cultivar was planted at the wider intra-row spacing of 30 cm (5.6 plants m-2 ) with finger millet at the closer intra-row spacing of 5 cm (33.3 plants m-2 ). This treatment also gave significantly (P<0.05) higher estimated total yield than that from the pure stand of finger millet indicating that the highest yield advantage from a pigeonpea/finger millet intercrop was influenced by the pigeonpea cultivar.

Yields from first season 1998 were significantly better than from the second season of 1997 indicating the influence of the amount of rainfall in the seasonal effect on the productivity of the pigeonpea/finger millet intercrop. The second season of 1997 had a mean monthly rainfall of 220.4 mm with a daily mean rainfall ranging from 1.96 to 10.98 mm while the second season of 1998 had 111.74 mm with a daily variation from 1.44 to 5.9 mm. The results of estimated total yields per hectare suggested that the pigeonpea/millet intercrop require low pigeonpea and high millet stand for better productivity per unit area. This explains productivity trends in the adopted traditional farming system where farmers regard finger millet as the main crop and the pigeonpea component as a minor crop (Ali, 1990).

The influence of the effect of plant row arrangement on the performance of pigeonpea and its sorghum intercrop are shown in Table 7. The plant row arrangement significantly (P<0.05) influenced all the yield and yield component characters within the pigeonpea cultivars KAT 60/8, ICPL 87091 and ICP 6927 used in the intercrops. The highest number of branches for KAT 60/8 and ICPL 87091 were obtained in a 2:2 row arrangement and the least branching in a 1:1 row arrangement. The high number of branches in a 2:2 arrangement could be attributed to a wider space which minimised competition from the sorghum for moisture, nutrients and light (Ali, 1990).

Table 7. Means of yield components of pigeonpea and yield of component crops obtained during 1997 at MUARIK

Treatments1

Pigeonpea

Yield (kg ha-1)

Total LER

Branches plant-1

Pods plant-1

100-seed weight (g)

Pigeonpea

Sorghum

Combined

PP1+S (1:1)

4.4

30.3

15.9

333

1912

2245

0.91

PP1+S (1:2)

5.0

35.3

14.0

417

2575

2992

1.20

PP1+S (2:2)

5.6

39.4

15.6

506

3550

4056

1.57

PP2+S (1:1)

4.2

20.3

14.7

383

1892

2275

0.88

PP2+S (1:2)

4.8

29.6

15.5

600

3304

3904

1.45

PP2+S (2:2)

5.9

33.7

14.7

750

3325

4075

1.62

PP3+S (1:1)

4.9

29.6

14.9

256

2054

2310

0.98

PP3+S (1:2)

5.0

26.6

14.0

375

1979

2354

1.15

PP3+S (2:2)

6.0

34.6

15.0

379

3025

3404

1.45

SolePP1

7.4

66.6

15.7

878

-

878

1.00

SolePP2

6.0

54.6

13.8

1083

-

1083

1.00

Sole PP3

6.7

60.6

14.2

629

-

629

1.00

Sole S

-

-

-

-

3575

3575

1.00

LSD (0.05)

0.78

5.31

NS

48.46

230.7

242.9

-

CV (%)

8.67

9.60

11.33

6.13

4.94

4.45

-

1Refer to Table 2;PP1 = KAT 60/8 (pigeonpea),PP2= ICPL 87091 (pigeonpea), PP3= ICP 6927 (pigeonpea) and S= SEREDO (sorghum); NS= Not significant at P=0.05

Number of pods per plant was significantly (P<0.05) influenced by plant row arrangement. Highest number of pods for each pigeonpea cultivar was obtained in the 2:2 row arrangement, and the lowest was in the 1:1 row arrangement. Highest number of pods obtained in the 2:2 row arrangement was due to less shading effect from the pigeonpea itself and the component crops thus allowing increased pod bearing on lower branches as light could reach the lower parts of the pigeonpea canopy (Ali, 1990).

Estimated grain yield of the pigeonpea cultivars KAT 60/8, ICPL 87091 and ICP 6927 were significantly (P<0.05) reduced due to inter-cropping, and plant row arrangement had a significant (P<0.05) effect on yield. The 2:2 row arrangement of pigeonpea and sorghum gave higher estimated yields of all the pigeonpea cultivars than in 1:1 and 1:2 row arrangements. Similarly, the 2:2 row arrangement gave better estimated sorghum yields without reducing the pigeonpea yield as much as was observed in the 1:1 and 1:2 row patterns.

The land equivalent ratio (LER) values suggested that the yield advantage of intercropping pigeonpea and sorghum was mainly from 1:2 and 2:2 row arrangements. The yield advantage was 19-57% in intercropping of KAT 60/8, 47-63% in intercropping of ICPL 87091, and 15-45% in intercropping of ICP 6927, with sorghum. Maximum yield (4075 kg ha-1) and yield advantage (63%) was obtained by growing ICPL 87091 and Seredo together in a 2:2 row arrangement. Higher yield advantages (45%) for ICP 6927 and (57%) for KAT 60/8 were also obtained from a 2:2 row pattern. Higher yield advantages obtained from the double rows of pigeonpea grown between double rows of sorghum was due to efficiency in use of resources such as light, water, and soil nutrients between the crops in association (Willey et al., 1981). Rao and Willey (1983) and Ali (1990) reported that crops grown in paired rows yield more than those grown in uniformly spaced rows because 2:2 row arrangement of crops allows more radiation to reach the lower part of the canopy and minimises competition. In the second season 1997, the LERs of intercropping systems under 1:1 were close to 1.0, indicating no land-use advantage of intercropping pigeonpea and sorghum during this season (Willey, 1979). Natarajan and Willey (1985) reported similar results from intercropping of pigeonpea with sorghum in that arrangement.

Table 8 shows the effect of plant row arrangement on the performance of pigeonpea and its sorghum and finger millet intercrops during the first season of 1998. As was the case in 1997, number of branches for KAT 60/8 and ICPL 87091 intercrops were significantly (P<0.05) affected by the plant row arrangement. The highest number of branches for KAT 60/8 and ICPL 87091 were again obtained in a 2:2 row arrangement and the least branching was in a 1:1 row arrangement.

Table 8. Means of yield components of pigeonpea and yield of component crops during first rains season of 1998 at MUARIK

Treatments1

Yield components of pigeonpea

Yield (kg ha-1)

Total LER

Branches plant-1

Pods plant-1

100-seed mass (g)

Pigeonpea

Finger millet

Sorghum

Combined

PP1+FM (1:1)

4.7

30.2

16.2

864

640

-

1504

1.30

PP1+FM (1:2)

6.3

22.3

15.6

669

636

-

1305

1.16

PP1+FM (2:2)

9.0

31.8

14.9

907

839

-

1746

1.54

PP2+FM (1:1)

3.7

12.6

6.3

588

722

-

1310

1.37

PP2+FM (1:2)

4.3

18.1

7.1

391

928

-

1319

1.38

PP2+FM (2:2)

6.3

19.7

11.1

1010

701

-

1711

1.79

PP1+S (1:1)

4.3

21.5

10.9

433

-

1807

2240

0.95

PP1+S (1:2)

4.7

21.3

11.4

404

-

2594

2998

1.21

PP1+S (2:2)

6.0

23.7

14.0

777

-

2220

2997

1.35

PP2+S (1:1)

3.3

9.5

5.2

349

-

1547

1896

0.91

PP2+S (1:2)

4.7

7.3

6.3

334

-

1865

2199

1.00

PP2+S (2:2)

5.7

10.3

4.0

632

-

2247

2879

1.45

SolePP1

8.7

51.5

24.5

1359

-

-

1359

1.00

SolePP2

7.3

20.6

11.5

956

-

-

956

1.00

Sole FM

-

-

-

-

958

-

958

1.00

Sole S

-

-

-

-

-

2848

2848

1.00

LSD (0.05)

0.96

1.05

0.90

96.1

113.6

121.9

122.5

-

C.V (%)

10.53

3.18

5.11

9.05

5.04

5.04

3.52

-

1Refer to Table 3;PP1 = KAT 60/8 (pigeonpea),PP2= ICPL 87091 (pigeonpea), FM= PESE 1 (finger millet) and S= SEREDO (sorghum)

The number of pods also were significantly (P<0.05) influenced by plant row arrangement with higher pod numbers for all the pigeonpea cultivars being observed in the 2:2 row arrangement. Unlike in 1997, the 100-seed weights of pigeonpea were significantly (P<0.05) affected by different intercrops and plant row arrangement in 1998 (Table 8). The mean seed weights of the pigeonpea cultivars intercropped with sorghum were higher in 1997 than in 1998, suggesting that pigeonpea cultivars were less subjected to competition from the cereal component crop during 1997 than in 1998.

Intercropping and plant row arrangement effects were significant (P<0.05) on estimated grain yield of pigeonpea, finger millet and sorghum (Table 8). In this season also a 2:2 row planting of pigeonpea gave higher estimated yields of finger millet and sorghum than 1:1 and 1:2. Grain yield of both the pigeonpea cultivars KAT 60/8 and ICPL 87091 were also significantly (P<0.05) reduced by intercropping.

The land equivalent ratio (LER) values suggested the existence of yield advantage of intercropping pigeonpea and finger millet or sorghum except in the case of pigeonpea planted with sorghum in a 1:1 row arrangement. The yield advantage was 15-31% in intercropping of KAT 60/8, and 37-79% in intercropping of ICPL 87091 with finger millet and 21-35% in intercropping of KAT 60/8, and 0-45% in intercropping of ICPL 87091 with sorghum (Table 8). The maximum yield advantage (79%) was obtained by growing pigeonpea cultivar ICPL 87091 and finger millet in a 2:2 row arrangement.

Insect damage and chemical spray studies indicated that both cultivars ICPL 87091 and KAT 60/8 suffered significantly (P<0.05) more seed damage from spraying in the vegetative stage only or no spray at all (Table 9). Continuous spray from vegetative stage to pod formation did not control pod sucking bugs in ICPL 87091 better than the control, while spraying at vegetative stage alone or at flower stage to pod maturity in KAT 60/8 did not control the pod sucking bugs better than no spraying. Spraying at only vegetative stage in ICPL 87091 did not reduce seed damage by both pod borers and podfly compared to the controls. At all spraying regimes, pigeonpea gave higher grain yields than unsprayed (control), but yields obtained by spraying at only vegetative stage were not significantly different from the controls. The highest yield in ICPL 87091 and KAT 60/8 were obtained when spraying was done at flower bud initiation to pod formation and at pod formation to pod maturity, respectively. Cultivar ICPL 87091 is determinate and therefore highly vulnerable to flower destroying insects while KAT 60/8 is indeterminate and can compensate for flowers destroyed.

Table 9. Seed damage by insect pests under different spray regimes and pigeonpea growth stage, and yield at Ngetta, 1998

Insecticide spray regime

Sole ICPL 87091

Sole KAT 60/8

% seed damage by

Total seed damage

Yield
(kg ha-1)

% seed damage by

Total seed damage

Yield
(kg ha-1)

Pod sucking bugs

Borers

Podfly

Pod sucking bugs

Borers

Podfly

1-0-0-0

4.7

3.9

6.0

14.6

2367

12.8

3.5

2.6

18.9

2588

1-1-1-1

4.0

1.3

1.0

6.3

2522

6.5

0.6

1.0

8.1

2856

0-1-1-0

3.3

3.1

2.1

8.5

2797

7.2

2.4

1.0

10.6

2854

0-0-1-1

2.1

1.0

1.0

4.1

2624

9.1

0.3

1.0

10.4

3030

0-0-0-0

5.4

5.2

6.1

16.7

1967

11.9

3.6

3.9

19.4

2127

LSD(0.05)

2.3

1.4

2.0

2.9

541

3.8

0.2

0.7

5.0

714

C.V(%)

22.11

27.40

27.91

22.59

15.40

21.23

24.97

24.81

21.34

14.62

0 = unsprayed, 1= sprayed

The results of cost-benefit ratios for spraying pigeonpea at various stages of growth are presented in Table 10. Spraying ICPL 87091 twice at flower bud initiation to pod formation (iii) and KAT 60/8 at pod formation to pod maturity (iv) with Nurelle-D was the most effective and economical with high cost-benefit ratios of 2.43 and 2.60, respectively. Minja (1996) reported little or no pesticide use to control insect pests in pigeonpea in Uganda because it was considered expensive. These results suggest that a judicious application of insecticides at the different critical stages of different cultivars is cost-effective.

TABLE 10. Benefit/cost ratio for spraying two pigeonpea varieties at various stages of growth under sole cropping system in 1998 at Ngetta

Item

ICPL 87091

KAT 60/8

i (4)

ii (8)

iii (2)

iv (2)

i (4)

ii (8)

iii (2)

iv (2)

Insecticide

6,000

12,000

3,000

3,000

6,000

12,000

3,000

3,000

Knapsack sprayerb

150,000

150,000

150,000

150,000

150,000

150,000

150,000

150,000

Labour for sprayingc

20,000

40,000

10,000

10,000

20,000

40,000

10,000

10,000

Labour for harvesting and threshing extra grainsd

20,000

27,750

41,500

32,850

23,050

36,450

36,350

45,150

Total cost

196,000

229,750

204,500

195,850

199,050

238,450

199,350

208,150

Extra yield (kg ha-1)

400

555

830

657

461

729

727

903

Revenuee

240,000

333,000

498,000

394,200

276,600

437,400

436,200

541,800

Profit

44,000

103,250

293,500

198,350

77,550

198,950

236,850

333,650

Benefit/cost ratio

1.22

1.45

2.43

2.01

1.39

1.83

2.19

2.60

i-iv indicates the stage of spray application and numbers in brackets = number of sprays applied
Exchange rate: US$ 1 = Ug.Shs 1,200; bCost calculated at 15% interest p.a. and depreciation over 5 years; cCost calculated at 2 man-days (Ug.Shs 5,000); d Cost calculated at 4 man-days (Ug.Shs 5,000) for every additional 100 kg; eCurrent average market price of pigeonpea, Ug.Shs 600/kg

CONCLUSIONS

Changing intra-row spacing significantly affected yield advantage of pigeon/cereal intercropping systems depending on the maturity group of the pigeonpea cultivars. Closer spacing for short duration and wider spacing for medium duration pigeonpeas cultivars had better land use for intercrops. Where moisture was not a constraint the inter-row spacing of 5 cm for finger millet and 15 cm for sorghum and wider inter row of 15-30 cm for pigeonpea was most advantageous. Yield advantage was also achieved when double rows of pigeonpea were planted in between paired rows of cereals. The study showed that spraying Nurelle-D twice at flower bud initiation to pod formation for short duration and pod formation to maturity for medium duration pigeonpea cultivars gave the most effective crop protection and best cost-benefit.

AKNOWLEDGEMENT

The research work reported in this paper was funded by European Union Contract No. ERBIC18CT960130.

REFERENCES

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©2000, African Crop Science Society

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