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Although Nigeria has no organized system of horticulture comparable to that of the developed world, a range of vegetables are grown casually as backyard crops. Many of these are both palatable and of good nutritional value, and have considerable potential as a supplement to a diet consisting mainly of starchy carbohydrates. To realise this potential, however, improved cultivars are necessary, as well as better crop management and the introduction of methods of preserving wet-season surpluses for use in the dry months.

Two maize cvs, FARZ 23 and FARZ 25, were grown at three densities (37,000, 53,000 and 80,000 plants/ha) in 1979 and 1980. Leaf area index (LAI) increased with increase in plant population and was at a maximum at mid-silk. Grain yield was highest at 53,000 plants/ha. There was no relation between LAI and grain yield but there was a positive correlation between LAI and total dry matter yield.Most farmers in the humid tropics grow their crops at wide and random spacings because of the system of cropping, which involves growing two or more crops together. These crops are introduced onto a piece of land at various times, and allowance is usually made for such introductions. However, as management practices improve and more farmers grow their crops sole, specific plant populations are more likely to be used.The situation in the ordinary farmer's plots is made even more complicated by his pattern of sowing 3-5 grains of maize per stand without thinning. Bartlett's (1980) survey of farming practice in the forest zone of Nigeria reported that one-third of farmers used a spacing of about 90 by 90 cm with 2-3 plants per stand; a smaller proportion (24%) reported a modified spacing of 90 by 60 cm; 15% used 75 by 75 cm; and none used the recommended 90 by 30 cm with one plant per stand. Such management practices are bound to affect the crop.The importance of plant density as a factor determining growth and yield of maize has been well established elsewhere (e.g. Ferry and Janick, 1971;Mock and Heghin, 1976;Moll and Kamprath, 1977;Milbourn et al., 1978) but only few reports are available from Nigeria (Fayemi, 1963;Chinwuba, 1967;Egharevba, 1977), where no definite recommendations are at present made. In a few research establishments and Ministries of Agriculture maize is grown at a population of 37,000 plants ha" 1 (90x30 cm), at which spacing improved maize varieties would probably not exploit the factors necessary for growth to the maximum. Hence this study examined the effect of density on growth and yield of maize.

FARZ 27, a high-yield maize variety, was grown in 1984 and 1985 over a wide range of density treatments (1-9-11-1 plants/m 2 ) and with four rates of nitrogen application (0, 75, 100 and 150 kg N/ha) in Ibadan. south-western Nigeria.There was no significant density or fertilizer effect on morphological characters of number of leaves per plant, height or stem diameter. For total dry-matter yield, the highest density of planting gave the highest yield although less dry matter was obtained in the 1985 experiment than in the 1984 experiment. Optimum density for grain production in both years was 8-8 plants/m 2 . There is an indication that there is no need to increase density of planting of maize beyond 80000 plants/ha in the south-western part of Nigeria. Plants without applied nitrogen fertilizer gave significantly lower total dry-matter and grain yields than plants with applied nitrogen. Highest grain yield was obtained with 150 kg N/ha in both years. By doubling the nitrogen application rate from the present recommended level of 75 kg N/ha to 150 kg N/ha an average increase of 0-42 t/ha of maize was obtained in both years. With the present prices of fertilizer and maize, this increase is economical. It seems therefore that more revenue would accrue to the farmers by using 150 kg N/ha on the 'FARZ series' of maize instead of the present recommendation of 75 kg N/ha.

The growth and development of two varieties of Phaseolus vulgaris (Purley King and Limelight) were compared in two experiments in 1973 and 1974 at a range of planting density from 20 to 100 seeds/m 2 . Within this range, the relationship between seed yield and density in Purley King was asymptotic, although there was a suggestion that if even higher densities had been tested, a downward trend in yield might have occurred. The optimum density of planting for Purley King in Expt 1 was 50 seeds/m 2 while that for Limelight was 40 seeds/m 2 . The corresponding densities in Expt 2 were 75 and 50 seeds/m 2 respectively. Although number of branches per plant generally decreased with increasing density, there was no significant density effect on the number of nodes per plant. Thus stabilization of seed yield occurred even at quite low densities. Although in the low-density treatments, less vegetative tissue was produced, the peak of dry-matter yield occurred later after flowering and the slower subsequent senescence ensured the presence of active photosynthetic tissue throughout the pod-fill stage. Less pod retention occurred at high density which, combined with the ability of widely spaced plants to produce pods over a longer period, resulted in a similar number of pods per unit area over a wide range of density.Although the variety Purley King produced more than double the number of mature pods from its extra nodes and branches, it was outyielded by Limelight by 35 % from the combined effect of more seeds per pod and a higher mean seed weight. Limelight also produced this high yield with less vegetative tissue. In both varieties it appeared that pod photosynthesis could take place, in Purley King because the pods were borne on higher nodes above the canopy and in Limelight due to the earlier senescence of its smaller leaf area. However, in spite of the apparent physiological advantages of Limelight, the pods are not borne high enough on this plant to enable satisfactory mechanical harvesting.