Effect of nitrogen fertilizer treatments on duration of senescense, harvest time and yield in some varieties of cowpea (Vigna unguiculata (L.) Walp)

The effects of liquid nitrogen fertilizer (150% N) and benzyl amino purine (BAP 200 ppm) on senescence, yield and nutrients mobilization in two cowpea varieties were investigated in the rainy and dry seasons. The study was conducted in a screen house at the University of Lagos, Nigeria (6°27ʺ1, 3°45ʺ E). The duration of the study was between August 2012 and January 2013. The experimental design used was completely randomized block design. The four treatments (nitrogen fertilizer, BAP, nitrogen fertilizer and BAP combination in 3:1 ratio and the control) were applied through foliar spray at 3, 6 and 9 weeks after planting and data on time of senescence and yield was collected. The days to 50% senescence, 90% senescence and death of the plants was earlier in IT89KD-288 than in Kanannado, while senescence started earlier in plant treated with liquid nitrogen fertilizer (15%N). For the first harvest, variety IT89KD-288 had higher number of pods (10), number of seeds (13) and length of pods (15.8 cm) than kanannado that had 8.0, 12.0, 14.68 cm, 3.17 and 18.53 for number of pods, number of seeds, length of pods, weight of grains per pod and weight of grains per plant, respectively, while at the second harvest, kanannado had higher number of pods (5), number of seeds (10), length of pods (12.12 cm), weight of grains per pod (2.68) and weight of grains per plant (12.03) than IT89KD-288 that had 4.0, 9.0, 11.31 cm, 2.05 and 11.27 for number of pods, number of seeds, length of pods, weight of grains per pod and weight of grains per plant, respectively. The combined treatment induced significantly greater yield than the other treatments. Yields were higher in the rainy season than dry season. The longer the duration of senescence, the higher the grain yield at the second harvest; therefore, confirming a direct relationship between senescence, harvest time and yield among cowpea varieties. Key words: Cowpea, benzyl amino purine, nitrogen, kanannado, fertilizer.