Response of Rainfed Sunflower (Helianthus annuus L.) to Nitrogen Rates and Plant Population in the Semi‐arid Savanna Region of Nigeria

Field experiments were conducted during the wet seasons of 1991,1992 and 1993 at the Abubakar Tafawa Balewa University Farm, Bauchi (10 ° 22‘N, 09 ° 47‘E) to study the response of sunflower (Helianthus annaus L.) to N rates and plant population under rainfed conditions. Four N rates (0, 50, 100 and 150 kg N ha ‐1) and four plant populations (40000,80000,120000 and 160000 plants ha‐1) were factorially combined in a randomized complete block design with three replications. Leaf area index, shoot dry weight and seed yield (kg ha‐1) increased significantly with increasing N rates from 0 to 100 kg N ha‐1. The growth and yield parameters per plant decreased significantly with increasing plant populations from 40000 to 160000 plants ha‐1, but the seed yield (kg ha‐1) obtained at 80000 plants ha‐1 was significantly higher than all the other plant populations. The interactions of N x plant population confounded the main effect of each factor on the growth and yield of sunflower. The seed yield (3425 kg ha‐1) obtained from the use of 100 kg N ha‐1 at 80000 plants ha‐1 was significantly higher than those obtained from all other combinations of N x population and out‐yielded the main effects of 100 kg N ha‐1 and 80000 plants ha‐1 by 18 % and 25 %, respectively. The use of 100 kg N ha‐1 at 80000 plants ha‐1 is therefore recommended for maximum yield of sunflower in Bauchi.