Response of sunflower (Helianthus annuus L.) to nitrogen application in a savanna alfisol

Decline in crop yield has been a major problem in Northern Guinea savanna zones of Nigeria due to inherent low fertility status of the soils. Field experiments were conducted for two years (2003 and 2004) on an alfisol of the Northern Guinea savanna of Nigeria to determine the effect of N fertilizer on growth and yield parameters of sunflower. Six rates of nitrogen (0, 30, 60, 90, 120, and 150 kg of N/ha) were applied. Plant height and number of leaves were highly significant 10 weeks after planting (WAP). Highest plant heights of 120 and 138 cm were obtained in 2003 and 2004, respectively, at 120 kg N/ha. Application of N significantly increased seed and oil yields while excess N (150 kg N/ha) reduced the contents of the two parameters. Optimum N requirement of sunflower obtained from this study is between 90 and 100 kg N/ha.