Nassr ع.م. and Assakkaf ع.ع. 2015. The effect of nitrogen and phosphorus fertilization on some vegetative growth of three sunflower (Heliathus annus L.) cultivars. University of Aden Journal of Natural and Applied Sciences. 19, 1 (Apr. 2015), 13–23. DOI:https://doi.org/10.47372/uajnas.2015.n1.a02.