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African Journal of Agricultural Research Vol. 6(7), pp. 1763-1770, 4 April, 2011 Available online at http://www.academicjournals.org/AJAR ISSN 1991-637X ©2011 Academic Journals Full Length Research Paper Performance of semi-determinate and indeterminate cowpeas relay-cropped into maize in Northeast Nigeria A. Y. Kamara1, L. O. Omoigui2, S. U. Ewansiha1, F. Ekeleme3, D. Chikoye1 and H. Ajeigbe1 1 International Institute of Tropic
  African Journal of Agricultural Research Vol. 6(7), pp. 1763-1770, 4 April, 2011 Available online at http://www.academicjournals.org/AJAR ISSN 1991-637X ©2011 Academic Journals   Full Length Research Paper Performance of semi-determinate and indeterminate cowpeas relay-cropped into maize in Northeast Nigeria A. Y. Kamara 1 , L. O. Omoigui 2 , S. U. Ewansiha 1 , F. Ekeleme 3 , D. Chikoye 1  and H. Ajeigbe 1   1 International Institute of Tropical Agriculture, P. M. B. 3112, Sabo Bakin Zuwo Road, Kano, Nigeria. 2 Department of Plant Breeding and Seed Science, College of Agronomy, University of Agriculture, Makurdi, Nigeria. 3 College of Plant Health, Michael Okpara University of Agriculture, Umudike, Nigeria. Accepted 9 December, 2010   Field trials were conducted in 2005 and 2006 in Tilla (northern Guinea savanna) and Sabon-Gari (Sudan savanna) in northeast Nigeria to determine the performance of two improved cowpea varieties when relay-intercropped with early and late maize, 6 and 8 weeks after planting the maize. Grain yield, number of branches and number of pods per plant were higher for the variety IT89KD-288 than for IT97K-499-35, whether planted sole or relay-intercropped with maize. Grain yield was lower for IT97K-499-35 than for IT89KD-288 when relay-intercropped with maize irrespective of the maturity period of the companion maize crop. This may be due to the indeterminate growth habit and shade tolerance of IT89KD-288 which allowed a higher pod load than IT97K-499-35. However, relay-intercropping with early maize gave higher yield than relay-intercropping into late maize. Also relay-intercropping at 6 weeks after planting maize (WAP) gave a higher yield than relay-intercropping at 8 WAP. This therefore, suggests that introducing cowpea into short statured early maize may mean less competition for light and soil resources compared to taller late maize. Also introducing the cowpea earlier may allow the crop to make full use of soil moisture during the cropping season. Key words:  Cowpea, maize, grain, relay-intercropping, savanna, northeast Nigeria. INTRODUCTION Cowpea ( Vigna unguiculata   (L.) Walp.) is an important food legume and an integral part of traditional cropping systems in the semi-arid regions of the tropics (Singh et al., 2003). It is used for food and animal feed and improves soil fertility, thus it has become very valuable in areas where land use has become intensified. Cowpea has outstanding features: drought tolerance, shade tolerance, quick growth, and rapid provision of ground cover (Singh et al., 1997). These characteristics have made cowpea an important component of subsistence agriculture in the dry savannas of the sub-Saharan Africa *Corresponding author. E-mail: a.kamara@cgiar.org. Tel: +234 802 080 4809 or +234 703 118 4878. where it is grown as a companion crop with cereals and other food crops (Singh et al., 2003). In the semi-arid zone of West Africa, cowpea is grown both as sole crop and in mixed crop production systems (Blade et al., 1997). Although sole-cropped cowpea produces higher yields when insecticide spray is used, most farmers traditionally practice mixed cropping (Blade et al., 1997; Singh, et al., 2003). Some studies (Andrews, 1974; Steiner, 1982; Ofori and Stern, 1987) have reported that farmers practice mixed cropping to alleviate the effects of low soil fertility and drought, reduce damage from pests and diseases, and assure higher yield stability. Over the years, the International Institute of Tropical Agriculture (IITA) has developed diverse high yielding cowpea varieties with contrasting growth habit (Singh et al., 1997). Some of these varieties have been evaluated  1764 Afr. J. Agric. Res. Table 1.  Average monthly minimum and maximum temperature (°C) in Sabon-Gari and Tilla in 2005 and 2006. Sabon-Gari, 2005 Sabon-Gari, 2006 Tilla, 2005 Tilla, 2006 Min Max Min Max Min Max Min Max January - - 16.50 37.60 - - 20.23 35.03 February - - 17.50 37.30 - - 20.32 38.07 March - - 24.52 36.13 - - 23.19 36.05 April - - 28.87 32.40 - - 23.23 39.42 May 27.10 39.18 27.80 36.90 - - 21.06 37.13 June 25.50 35.00 22.92 38.15 25.87 35.61 20.50 36.37 July 24.46 32.91 22.31 36.87 23.90 34.93 20.68 34.23 August 23.27 33.09 21.87 33.87 21.19 37.48 20.32 33.00 September 23.63 34.06 21.68 35.97 22.66 34.60 19.97 33.40 October 23.85 35.93 21.27 38.87 21.80 36.58 20.61 35.81 November 21.80 36.73 16.48 38.62 22.18 34.34 20.13 33.57 December 22.82 36.33 23.28 34.07 21.12 32.77 20.16 38.06 under sole- and inter- cropping systems with millet and sorghum in the Sudan savanna zone of Nigeria (Singh et al., 1997; Singh et al., 2003), no work has been reported on their performance when they are relay-intercropped with maize. Maize production has increased tremendously in the Nigerian savannas because of its high yield potential and the crop is becoming important in the drier savannas, in particular where most of the cowpea grown is intercropped with cereals. Because of labour constraints and land scarcity, farmers prefer to relay-intercrop cowpea between 6 and 8 weeks after planting maize (WAP). When intercropped with maize or other cereals, cowpea yield is reduced by shading (Chang and Shibles, 1985; Fukai and Trenbath, 1993). A differential response by cowpea to shading has been reported due to different growth habits (Isenmilla et al., 1981; Nelson and Robichaux, 1997; Terao et al., 1997). The date of introduction into maize crop may also affect the productivity of cowpea. Thus, date of introduction of cowpea into maize is a management practice that may be manipulated to reduce the effect of shading (Olufajo and Singh, 2002). N’tare (1990) reported that the late introduction of early maturing cowpea varieties into millet reduced the grain yield of cowpea in Niger Republic. Several cowpea varieties have been developed for the Nigerian savannas but little information exists on the performance of these varieties when relay-intercropped with maize. Since most of the varieties were selected in sole cropping system, there is a need to evaluate their performance in the intercropping system that is predominant in the Nigerian savannas. This paper reports the results of experiments conducted in the Sudan (SS) and northern Guinea savannas (NGS) of northeast Nigeria to evaluate the performance of two popular cowpea varieties with contrasting growth habit and maturity period when relay-intercropped with maize on different dates. MATERIALS AND METHODS Site description Field studies were conducted at two locations, Sabon-Gari (10o 48.40’ N 12o 27.88’ E 458 m asl) in the SS and Tilla (10o 30.78’ N, 12o 03.56’ E 749 m asl) in the NGS, in northeast Nigeria during the 2005 and 2006 cropping seasons. The two sites have a unimodal rainfall pattern with annual rainfall mean of 976 mm for Sabon-Gari and 1425 mm for Tilla. Sabon-Gari has a growing period of about 120 days. The soil is loam with 8.3 g kg -1  organic carbon, 0.98 g kg -1  nitrogen, 4.0 mg kg -1  phosphorus, 0.32 Cmol (+) kg -1  potassium and a pH of 5.4. Tilla has a growing period of about 150 days. The soil is sandy clay with 9.8 g kg -1  organic carbon, 1.7 g kg -1  nitrogen, 1.6 mg kg -1  phosphorus, 0.51 Cmol (+) kg -1  potassium, and a pH of 5.65. The temperature and rainfall during the trial period are given in Table 1 and Figure 1. Treatments The experiment was set up as a split-split plot design with the date of cowpea introduction into maize as the main plot, cropping systems as subplot, and cowpea variety as sub-subplot. The cropping systems were cowpea relay-intercropped with early maturing maize (TZE COMP5-W), cowpea relay-intercropped with late maturing maize (97 TZL COMP1-W), with sole cowpea as the control. Two cowpea varieties with contrasting growth habit (IT89KD-288, indeterminate; IT97K-499-35 semi-determinate) were introduced into maize crop 6 and 8 weeks after maize was planted. The two cowpea varieties were also sole-planted at the time of introduction into the maize crop to serve as controls. Planting and cultural practices Before the first crop was established, the field was disc-harrowed and ridged. In 2005, maize was planted on 10 July at Sabon-Gari and on 05 July at Tilla. In 2006, maize planting was done on 21 June at Sabon-Gari and on 19 June at Tilla. Three maize seeds were planted on ridges 0.75 m apart at an intra-row spacing of 0.50 m and later thinned to 2 plants per hill to give a population of 53,333 plants ha -1 . A mixture of Paraquat (1:1-dimethyl- 4, 4’-bipyridinium dichloride; Manufacturer: Syngenta Crop Protection  Kamara et al. 1765 Figure 1.  Mean monthly rainfall in Sabon-Gari and Tilla in 2005 and 2006. Table 2.  Dates of introduction of cowpea into maize. Date of introduction 2005 2006 6 weeks after maize Sabon-Gari 21 August 02 August Tilla 16 August 31 July 8 weeks after maize Sabon-Gari 02 September 16 August Tilla 30 August 14 August Canada Inc.) at the rate of 276 g a.i.L -1  and Primextra (Syngenta Crop Protection Canada Inc.) at the rate 3 L ha-1 was applied as a pre-emergence herbicide to control weeds. Hoe weeding was done at 3 WAP. At planting, fertilizer in the form of NPK 15:15:15 was applied at the rate of 40 kg ha -1  to all plots. Nitrogen fertilizer was top dressed in the form of urea at the rate of 60 kg N ha -1  at 5 WAP of maize. Cowpea was planted 6 and 8 weeks after maize (Table 2). Three seeds of cowpea were planted between two hills of maize which is equivalent to 0.50 m between two hills of cowpea. The cowpeas were later thinned to 2 plants per hill to give a population of 53,333 plants per ha. Sole cowpea was planted on ridges 0.75 m apart with intra-row spacing of 0.50 m and two plants per hill to give a cowpea population similar to that of maize. Insect pests of cowpea were controlled by spraying cowpea plants with Best Action (30 g L -1  cypermethrin + 250 g L -1  dimethoate; Manufacturer: Modern Insecticides Ltd, India)) at the rate of 1L ha -1  during floral bud formation, flowering, and podding stages. Measurements At harvest five cowpea plants were randomly selected from the two middle rows to determine the number of pods per plant. Branches on the five plants were counted and the total number was divided by five to determine the number of branches per plant. The two central rows were harvested when the first flush of pods were mature and dry. Grain yield was based on all plants that were harvested from the two central rows of each plot and was reported on a 100% dry matter basis. Data analysis  All data were subjected to an ANOVA using the PROC MIXED procedure (Littell et al., 1996) of SAS (SAS Institute, 1995) with the cowpea variety analyzed as sub-subplot, dates of cowpea introduction as subplot, and cropping systems as main plot. Block was treated as a random effect; dates of cowpea introduction and cowpea varieties were treated as fixed effects in determining the expected mean square and appropriate F test in the analysis of variance. Differences between two treatment means were compared with the t-test based on the SED at 5% level of probability. RESULTS Cowpea grain yield The three-way interactions among the date of introduction of cowpea into maize crop (D), cropping system (C) and variety (V) were significant for cowpea  1766 Afr. J. Agric. Res. Table 3.  P values for the combined ANOVA for grain yield (kg ha -1 ), branches plant -1 , and pods plant -1  of cowpea planted sole and relayed into early and late maturing maize at Sabon-Gari and Tilla in Borno State, northeast Nigeria. Grain yield(kg ha -1 ) Branches plant -1  Pods plant -1  Effect SBG† Tilla SBG Tilla SBG Tilla Year (Y) 0.6467 0.0012 0.0001 <.0001 0.0132 0.1867 Cowpea relay date (D) 0.0003 0.2553 0.0315 0.0268 0.0386 0.1398 Y × D 0.5522 <.0001 <.0001 0.7394 <.0001 0.2598 Cropping system (C) <.0001 <.0001 <.0001 <.0001 <.0001 <.0001 Y × C 0.0038 0.0011 0.0013 0.0275 0.0429 0.5003 D × C 0.1884 0.4438 0.0067 0.0470 0.6260 0.4130 Y × D × C 0.7671 0.2400 0.0010 0.0094 <.0001 0.2739 Variety (V) <.0001 <.0001 <.0001 <.0001 <.0001 <.0001 Y × V 0.0003 0.2541 0.0282 0.0684 0.0002 0.1604 D × V 0.0045 0.0214 0.7189 0.1417 0.0171 0.2057 C × V <.0001 0.2688 0.5661 0.9756 0.5003 0.0646 Y × D × V 0.1961 0.6218 <.0001 0.0513 <.0001 0.0302 Y × C × V 0.0606 0.0009 0.0861 0.0058 0.0952 0.5788 Y × D × C 0.1961 0.6218 <0.0001 0.5136 <0.0001 0.0302 D × C × V 0.0003 0.0912 0.5872 0.6142 0.1576 0.2563 Y × D × C × V 0.0940 0.1282 0.3380 0.6221 0.1338 0.0405 †SBG = Sabon-Gari. Table 4.  Effect of time of cowpea introduction, cropping system and variety on cowpea grain yield (kg ha -1 ) at Sabon-Gari and Tilla in Borno State, northeast Nigeria. 6wap 8wap Cropping system IT89KD-288 IT97K-499-35 Mean IT89KD-288 IT97K-499-35 Mean Sabon-Gari Early maturing maize 1716.4 486.7 1101.5 1162.3 499.6 831.0 Late maturing maize 1301.1 338.0 819.5 986.6 483.0 734.8 Sole cowpea 1325.7 1272.4 1299.1 1340.5 1011.3 1175.9 Mean 1447.7 699.0 1163.1 664.7 S.E.D ( D × C) ‡ 74.86 S.E.D (D×V) 60.87 S.E.D (C × V) 74.86 S.E.D (D × C × V) 107.17 Tilla Early maturing maize 1266.9 771.9 1019.4 1037.4 867.9 952.7 Late maturing maize 1133.1 449.8 791.5 844.8 510.7 677.7 Sole cowpea 1522.5 1099.8 1311.1 1570.6 1103.6 1337.1 Mean 1307.5 773.8 1150.9 827.4 S.E.D (D × C) 77.05 S.E.D (D × V) 63.67 S.E.D (C × V) 77.98 S.E.D (D × C × V) 107.62 ‡D = Time of cowpea introduction, C = cropping system, V = variety. grain yield in Sabon-Gari but not in Tilla (Table 3). At both times of introduction of cowpea into maize crop (6 and 8 WAP), IT89KD-288 produced a higher grain yield than IT97K-499-35 in both locations (Table 4). Grain yield of IT97K-499-35 was higher when sole-cropped than when relay-intercropped into early and late maize at all times of
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