Helmy, Ayman M., and Mohamed Fawzy Ramadan. “Agronomic Performance and Chemical Response of Sunflower (Helianthus Annuus L.) to Some Organic Nitrogen Sources and Conventional Nitrogen Fertilizers under Sandy Soil Conditions”. Grasas y Aceites 60, no. 1 (March 30, 2009): 55–67. Accessed February 8, 2023. https://grasasyaceites.revistas.csic.es/index.php/grasasyaceites/article/view/546.