Field experiments were carried out between September and December in 2007 and 2008 at Akamkpa (15° 15'' N; 8° 22'' E), Nigeria. The objective was to investigate the productivity of maize and soybean as sole crops and as additive mixtures (100:100) in response to five levels of nitrogen (0, 25, 50, 75 and 100 kg/ha) and five crop arrangements (sole maize at 53,333 plants/ha, sole soybean at 266,666 plants/ha and maize: soybean intercrop arrangements of 1:1, 2:2 and 1:2). The trial was a split-plot design in a randomized complete block with nitrogen in main plot and crop arrangement in sub-plot, with three replications. Nitrogen fertilization increased yield in both maize and soybean at all the treatment levels, when grown sole or in mixtures. Application of 100kg N/ha to maize increased number of ears per plant, cob diameter, cob length, 100-grain weight, cob yield and grain yield by 46, 106, 95, 35, 138 and 153 percent, respectively in 2007, and by 15, 33, 63, 48, 88 and 109 percent, respectively in 2008, over no nitrogen application. Similarly, application of 100kg N/ha to soybean increased number of pods per plant, number of barren pods and 1000-seed weight by 53, 120 and 16 percent, respectively in 2007, and by 55, 99 and 14 percent, respectively in 2008, over no nitrogen application. Optimum seed yield in soybean was obtained at 50 kg N/ha. The yield values of 1,352.8 and 1,158.2 kg/ha were higher than those obtained at 0 kg N/ha by 31 and 21 percent in 2007 and 2008, respectively. Increasing the nitrogen level further to 100 kg/ha depressed seed yield by 8 percent in 2007 over 0 kg/ha. The nitrogen x crop arrangement interaction effects on grain yield and all other parameters were not significant (p< 0.05). Late season maize and soybean may be planted at 50 kg N/ha to take advantage of optimum soybean seed yield and 66-76 percent of the maize grain yield. Keywords: maize, soybean, intercropping, additive mixtures, interplant arrangement
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