Growth and Yield Response of Sunflower (Helianthus annuus l) to Spacing and Nitrogen Fertilization in Southern Guinea Savanna Ecological Zone of Nigeria

The experiments were conducted during 2016 and 2017 rainy season; to determine the optimal rate of nitrogen fertilizer and adequate plant spacing for production of sunflower in southern guinea savanna agroecology zone of Nigeria. The treatments consisted of planting spacing three (20cm, 30cm, 40), four levels of nitrogen fertilizer (0, 80, 100 and 120 N Kg ha -1 ). A factorial experiment laid in a Randomized Complete Block Design (RCBD) and replicated three times. The results showed that planting at 40cm significantly produced plants with higher number of leaves; the tallest plants (57.86 and 58.21cm) and bigger plants with stem girth of 2.93cm and 2.94cm respectively. The shortest plants (51.82 and 52.34cm) and the smallest stem girths (2.03 and 2.08cm) were recorded on sunflower that were planted on 20cm plant spacing in both years of cropping. Application of 120 N kg ha -1 significantly produced sunflower plants with the highest number of leaves (18.76 and 18.83), tallest sunflowers (60.45 and 61.23cm) and biggest stem girth of 3.03 and 3.12cm in both 2016 and 2017 cropping seasons. These results above were at par with the other rates of nitrogen fertilizer application, but higher than the control plots. Sunflower planted at 40cm apart also significantly produced the heaviest head weight per plant of 149.40 and 152.30g; seed weight per head (78.12 and 87. 66 g) and seed yield  of 512. 45 and 524.21 kg ha -1 . Application of 120 N kg ha -1 produced the highest seed yield of 561.59 and 549.42 kg ha -1 of sunflower in both cropping seasons. This result is statistically at par with application rates of 100 N kg ha -1 which produced 557.41 and 547.06 kg ha -1 seed yield of sunflower; and also the same with application of rate of 80 N kg ha -1 which produced 528.87 and 525. 10 kg ha -1 seed yield of sunflower in both cropping seasons. The control plots produced the lowest seed yield (312.89 and 322.23 kg ha -1 ) in both years of cropping. It can be concluded that 80 N kg ha -1 is the optimal nitrogen requirement and planting at 40cm apart is adequate plant spacing for production of sunflower in southern guinea savanna agroecology zone of Nigeria.  Keywords: Fertilizer, Growth, Nitrogen, Spacing, Sunflower, Yield.