Grain yield and yield components of single, double, and synthetic maize lines grown at four N levels in three ecological zones of West Africa

The objective of this research was to determine the responses of 10 maize cultivars (six single-cross hybrids, three double-cross hybrids, and one synthetic cultivar) to N fertilization in West Africa. Factorial combinations of N rates (0, 7, 140, and 210 kg N ha(-1)) and 10 maize cultivars were studied in a split-plot design. The study was conducted in 1991 at Mokwa (9 degrees 18' N, 5 degrees 04' E) and Samaru (11 degrees 11' N, 7 degrees 38' E), and in 1992 at Ikenne (6 degrees 55' N, 3 degrees 55' E), Mokwa (9 degrees 18' N, 5 degrees 04' E), and Kaduna (10 degrees 36' N, 7 degrees 27' E), to represent the forest, southern, and northern Guinea savannah ecological zones of West Africa, respectively. Cultivars responded differently to N with respect to grain yield, with the hybrids producing higher yields than the synthetic cultivar. Forest ecology had the lowest grain yield when compared with savannah ecologies. Marked differences existed among the ecologies in maize grain yield response to N with Samaru and Kaduna having the highest response at 210 kg N ha(-1), while responses of 70 and 140 kg N ha(-1) were obtained at Ikenne and Mokwa, respectively. Most cultivars had similar values for most of the yield component parameters, except for ear length, harvest index, and total dry matter (DM), where the hybrids had greater values than the synthetic cultivar. However, cultivars that had higher values in total DM, 100-kernel weight, and harvest index had higher grain yield. Cultivar 1386 x KU1414-SR performed the best among the cultivars evaluated in terms of grain yield.