Sfredo G, Sarruge J, Haag H. Absorption of nutrients by two cultivars of sunflower plants (Helianthus annuus L.) under field conditions: I. Macronutrients concentration . An. Esc. Super. Agr. Luiz de Queiroz. 1983;40(2):1135-1163. doi:10.1590/S0071-12761983000200019