Studies on performance of some open-pollinated maize cultivars in the Guinea savanna zone of Ghana. 1. Effects of plant density, nitrogen level and their interactions on yield
AbstractPlant density and nitrogen (N) fertilizer responses of one local and three improved open-pollinated cultivars of maize (Zea mays L.) developed in different eras of maize breeding were studied on sandy-loam Alfisols in the Guinea savanna zone of Ghana in 1992 and 1993. A split-plot design was used in which plant densities (30 000, 50 000, 70 000 plants/ha) were the main-plots and 12 combinations of N fertilizer levels (0, 80, 160 kg N/ha) and cultivars (Local, Composite 4, Dobidi, Okomasa) were the sub-plots in four replicates. A cross location analysis for grain yield showed environment, plant density, nitrogen and cultivar effects were highly significant (P<0.01). The environment W ultivar, environment W nitrogen, density W nitrogen, and nitrogen W cultivar interactions were also significant (P<0.05). The density W cultivar interaction and all second- and third-order interactions involving the three factors were not significant. The mean yields were 3.08 and 4.51 t/ha for the local and the improved cultivars, respectively. For all cultivars, yields increased by 10 per cent after each 20 000 plants/ha increase in plant density. Similar N response patterns were observed for all the improved cultivars. Estimated biological optimum N rates were 154 kg N/ha for the local cultivar and 183 kg N/ha for the improved cultivars. Grain yields at the optimum N levels were 3.50 t/ha for the local and 5.53 t/ha for the improved cultivars. The greatest yield response to N was observed at 80 kg N/ha for all cultivars. The data showed that (1) improved cultivars out-yielded the local cultivar at low as well as at higher levels of soil fertility, (2) breeding did not result in varieties that required higher N rates to produce high yields, and (3) the data support the current N fertilizer recommendations for the Guinea savanna zone of Ghana.
Ghana Jnl agric. Sci. Vol.30(2) 1997: 151-159
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