Cowpea [Vigna unguiculata (L.) Walp.] is one of the important food legumes and a valuable component of traditional cropping systems in semiarid tropics (Henriet et al., 1997; Mortimore et al., 1997). It makes a valuable contribution toward human food and livestock fodder. As human food, cowpea can provide both vegetable and grain. This dual-purpose character has made it an attractive crop where land is becoming scarce (Singh et al., 2003). Its shade tolerance characteristic makes it compatible as an intercrop with maize, millet, sorghum as well as with several plantation crops (Singh and Emechebe, 1998). These characteristics have made cowpea an important component of subsistence agriculture in the semiarid tropics of Africa, Latin America, and Southeast Asia.
In many cowpea-growing areas of Africa and Asia, the crop is mainly grown by small-scale farmers who practice intercropping to maximize productivity on their small land holdings. Thus, although monocrop cowpea is profitable, farmers plant cowpea in various types of intercropping systems (Singh et al., 2003). Under such cropping systems, cowpea not only offers diversification in available food stuffs, but also serves as a security crop in case of failure of the main crops.
Two main systems are commonly used in the production of cowpea. Where the crop is grown purely for vegetable production, the entire plant is uprooted at the three to five true leaf stage before the leaves become too mature and fibrous. In the case of dual-purpose production, sequential leaf harvests are made during the vegetative stage of the crop followed by seed harvesting at the end of the season. The latter system predominates with most subsistence growers who practice intercropping. However, there is paucity of information on the effects of leaf harvesting on nitrogen composition and subsequent productivity of most cowpea–cereal-based cropping systems.
Defoliation influences tissue nitrogen content and subsequent yields of companion crops in an intercrop system. Nyeko et al. (2004) recorded increased maize shoot nitrogen content and yield with increase in defoliation intensity of a companion alder crop. In contrast, alder shoot nitrogen content was significantly decreased with increase in defoliation intensity. No information is available on how tissue nitrogen content and yield of companion crops of a dual-purpose cowpea–maize intercrop are influenced by leaf harvesting initiation time and frequency of the cowpea component at its vegetative stage. Also, information is lacking on the effects of harvesting cowpea leaves at the vegetative stage of the crop on individual crop performance in a dual-purpose cowpea–maize intercropping system. Moreover, studies on cowpea–cereal-based intercropping systems have mostly concentrated on grain yield, ignoring the potential vegetable yields and how these yields could influence the overall productivity of such systems (Rao and Mathuva, 2000; Reda et al., 2005; Rusinamhodzi et al., 2006). The objectives of this study were, therefore, to determine the effects of leaf harvesting initiation time and frequency of cowpea on 1) tissue nitrogen content of companion crops in a dual-purpose cowpea–maize intercrop; and 2) cowpea and maize yield and the overall productivity of a cowpea–maize intercrop measured by land equivalent ratios (LER).
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Mortimore, M.J. Singh, B.B. Harris, F. Blade, S.B. 1997 Cowpea in traditional cropping systems 99 113 Singh B.B. Mohan Raj D.R. Dashiell K. Jackai L.E.N. Co-publication of International Institute of Tropical agriculture (IITA) and Japan International Center for Agricultural Sciences (JIRCAS), IITA Ibadan, Nigeria
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Singh, B.B. , Ajeigbe, H.A. , Tarawali, S.A. , Fernandez-Rivera, S. & Abubakar, M. 2003 Improving the production and utilization of cowpea as food and fodder Field Crops Res. 84 169 177
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Singh, B.B. Emechebe, A.M. 1998 Increasing productivity of millet–cowpea intercropping systems 88 95 Emechebe A.M. Ikwelle M.C. Ajayi O. Amino Kano M. Anosa A.B. Proc. of the Pre-season Planning Meeting for the Nationally Coordinated Research Programme for Pearl Millet, Maidiguri 21–24 April 1997 Lake Chad Research Institute Maiduguri, Nigeria
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