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Experiments were conducted in Nigeria to evaluate the optimum plant population density for okra (Abelmoschus esculentus) sown in monoculture or intercropped with cassava (Manihot esculenta). The crops were sown as late and early season crops in 1997 and 1998. Okra was sown at varied spacings to achieve final plant densities of 25 000, 35 000 and 50 000 plants\ha in both monoculture and mixed stands. Intercropping had no significant effect on okra phenology (time to vegetative growth, flowering and fruiting). However, it significantly reduced weed growth by 25-45 % and nematode infection in okra by 36 %, and kept the canopy environment of cassava cooler by 3n0-4n4 mC and more moist by 5-10 g\kg, compared with monoculture. The durations of vegetative and reproductive growth and the weed-control ability of okra in both cropping systems were influenced by population density. Okra sown at 50 000 plants\ha took the longest time to reach specific phenological stages, controlled weeds best and gave the highest fresh pod yields in both seasons. There was little increase in pod yields between 35 000 and 50 000 plants\ha in mixed stands in late season sown crops. The growth and tuber yield of cassava were not significantly affected by intercropping and okra population density.The growth of okra and cassava were better with early than late season sowing, irrespective of okra population density or cropping system. This appears to have been due mainly to the effect of temperature and rainfall differences between the seasons. The substantial variation in the weather during the two seasons also had greater effect in monoculture than mixed stands. It is concluded that when rainfall is limiting, okra could be intercropped with cassava using population density up to 35 000 plants\ha to allow the vegetable to develop and to maximize pod yield under the relatively dry conditions. The optimum target suggested is 50 000-60 000 plants\ha during the wet periods.

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SUMMARYThe effects of various intercropping patterns of maize and melon on soil temperature and moisture content and crop growth and yield were compared in field trials over a two year period. Intercropping raised soil temperature in the upper 10 cm at 0600 h and reduced it at 1000, 1400 and 1800 h, and also increased soil moisture content by about 30%, compared with maize sole cropping. Melon biomass and seed yields were reduced by intercropping but maize growth characters were unaffected. However, the reduction in melon yields was less when grown with maize in widely spaced rows. Maize intercropped with melon in alternate pairs of rows (2:2) gave the best land equivalent ratio (LER).

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Nitrogen fertilization of okra (Abelmoschus esculentus) when intercropped with cassava (Manihot esculenta) and maize (Zea mays) was studied using three N rates (0, 60 and 120 kg/ha) in two field experiments in Nigeria between 1995 and 1997. The okra was grown between the cassava and maize rows. The effect of using two contrasting maize cvs. TZE Composite 3 Cl (less-tall, early-maturing with narrow leaves) and DMRSR-Y (tall, late-maturing with broad leaves) on N response of okra in the mixture was also investigated. Intercropping with maize or cassava and maize significantly increased stem elongation, delayed pod harvest, and decreased branch or pod formation and marketable pod yield in okra. In the cassava/maize/okra combination, maize had greater effect than cassava in determining most growth and pod yield attributes of the okra crop, regardless of N rate. However, the effect was relatively less severe in mixtures with early-maize cv. TZE Composite 3 Cl than with late-maize cv. DMRSR-Y. Although applied N at rates above 60 kg/ha in intercropping increased maize grain and cassava tuber yields, this did not result in a further significant gain in pod yield of the associated okra crop. The present recommendation of 60 kg/ha for N fertilization of cassava/maize intercrop was found to be applicable to okra grown between the cassava/maize rows using the less-tall, early-maize cultivar with relatively narrow leaves, and possibly reduced leaf area.