Field experiments were conducted during the wet seasons of 1986 and 1987 at the Yandev Agricultural Experiment Station to investigate the effects of component density on the yield of sorghum or maize intercropped with soybean. Seed yield of the monocrops of sorghum, maize and soybean were higher than the individual components in the intercrops. Yields of component crops in the intercrop varied significantly with the components population density. The sorghum/soybean intercrops which had LER (Land Equivalent Ratio) up to 1.40 in 1986 and 1.35 in 1987 were more productive than soybean/maize intercrop with maximum LER of 1.28 and 1.34 respectively during 1986 and 1987. Similarly the ATER (Area X Time Equivalent Ratio) of sorghum/soybean was greater than in soybean/maize. However, for maximum productivity of sorghum or maize intercropped with soybean, optimum population of one component crop plus 1/2 optimum population of the companion crop is recommended depending on which of the crop is regarded as main or minor crop.

Nicotiana tabacum L. cv. Ky-14 plants were grown in an intermittently irrigated gravel culture system in a greenhouse. The nutrient variables were either Mo (0 to 0.66 μeq/l) or Mo (0 and 0.33 μeq/l) plus SO42− (0 to 0.50 meq/l). About 45 days after initiating the treatments, the plants were harvested and separated into leaves, midribs, stalk epidermis, stalk xylem–phloem, and stalk pith for Mo, S, NO3−, total N, and nitrate reductase (NR) (EC 1.6.6.1) activity assay. Other plants were grown in complete Hoagland's solution (i.e., 0.66 μeq Mo/l and 0.50 meq SO42−/l) for all nutrient elements and used for determinations of canopy and seasonal profiles of NR activity.Molybdenum concentration in all plant parts increased with increasing solution Mo concentration. Sulfate drastically reduced the concentration of Mo, and the inhibition was essentially equal in all plant parts. Greatest reduction of Mo occurred with the first increment of SO42− (0.05 meq/l), with little effects from further additions of SO42−. The data suggest that the inhibitory effects of SO42− on Mo content occur primarily during the absorption process, with some antagonistic mechanism involved during translocation from roots to leaves. Molybdenum was not inhibitory to S accumulation. Contents of Mo and S in leaves were greater than in any other plant part.NR activity generally increased from bottom to top leaves. About 60% of the NR in the plant occurred in the leaves. The canopy profiles suggest that the recent, completely open leaf (7–9 in. long) and the second and third leaves below it could be sampled for maximum NR activity for NO3− reduction experiments. Sulfate nutrition increased NR activity, as a result of increased NR synthesis, while Mo nutrition was without effect on NR in these experiments. The NO3− content was not affected by SO42−, but NO3− increased in the absence of Mo.

SUMMARYSeed yam production potential of three yam species (Dioscorea rotundata, Dioscorea alata and Dioscorea cayenensis) was assessed for two systems – the traditional method using 100 to 200 g setts, and the mini-sett technique using 25, 20, 15 and 10 g setts cut from mother tubers. The mini-sett technique required only 6–33% of the number of tubers needed for the traditional planting system, and resulted in plants superior to those produced by the traditional method in all their production attributes especially in the case of D. alata and D. rotundata.

Field experiments were conducted to determine the direct and residual contributions of legumes to the yield and nitrogen (N) uptake of maize during the wet seasons of 1994 and 1995 at the University Farm, Abubakar Tafawa Balewa University, Bauchi, Nigeria, located in the Northern Guinea savannah of Nigeria. Nodulating soybean, lablab, green gram and black gram contributed to the yield and N uptake of maize either intercropped with the legumes or grown after legumes as a sole crop. Direct transfer of N from the nodulating soybean, lablab, green gram and black gram to the intercropped maize was 24.9–28.1, 23.8–29.2, 19.7–22.1 and 18.4–18.6 kg N ha–1, respectively. However, the transfer of residual N from these legumes to the succeeding maize crop was 18.4–20.0, 19.5–29.9, 12.0–13.7 and 9.3–10.3 kg N ha–1, respectively. Four years of continuous lablab cropping resulted in yields and N uptake of the succeeding maize crop grown without fertilizer N that were comparable to the yields and N uptake of the succeeding maize crop supplied with 40–45 kg N ha–1 and grown after 4 years of continuous sorghum cropping. It may therefore be concluded that nodulating soybean, lablab, green gram and black gram may be either intercropped or grown in rotation with cereals in order to economize the use of fertilizer N for maize production in the Nigerian savannah.