Nitrogen and phosphorus fertilization of sunflower crop in alkaline Cambisol
ABSTRACT Sunflower is a crop that has aroused the interest of farmers because of its adaptability to wide climatic conditions and for its use in biodiesel production. However, there are only a few studies on sunflower fertilization in alkaline soils. This study aimed to evaluate nitrogen (N) and phosphorus (P) fertilization in sunflower (Helianthus annuus L.) cultivated in alkaline soil. A field experiment was carried out in Baraúnas-RN, Brazil, in a Haplic Cambisol derived from calcareous rock, where the sunflower H-251 hybrid was cultivated. The treatments were a combination of four doses of N (30, 60, 90 and 120 kg ha-1) and four doses of P2O5 (30, 60, 90 and 120 kg ha-1). Sunflower growth and yield increased with the doses of N and P2O5. Doses of 30 kg ha-1 of N and 30 kg ha-1 of P2O5 were more economical, corresponding to grain yield of 2378 kg ha-1. Critical levels associated with these doses of N and P2O5 were 28.2 g kg-1 for N leaf content, 2.84 for P leaf content, and 6.75 mg dm-3 for soil available P extracted by Mehlich-1.