Fertilizer N Recovery in Sunflower Crop and Interaction Between Bio and Inorganic Fertilization Using Stable ¹⁵N Isotope

A field experiment was done (randomized complete block design, 3 replicates) on the response of sunflower (Helianthus annuus, cv. Sakha 53) on a sandy soil, to bio and inorganic fertilization with application of ¹⁵N technique; during 2014 summer season under drip irrigation system involving two factors. Factor A: Inorganic fertilization :no N (N₀); 105 kg N ha^-1 (N₁ ); 140 kg N ha^-1 (N₂) and 175 kg N ha^-1 (N₃). Factor B: Bio fertilization: no bio fertilizer (B₀); Azotobacter chroococcum bio fertilizer (B1); Azospirillum brasilense bio fertilizer (B₂) and Bacillus megaterium in 3 replicates. The Azotobacter and Azospirillum are N₂-fixing bacteria (N₂-fixers) while B. megaterium are P-dissolving bacteria (PDB). Plot area 10 m².All plots received 21 Mg ha^-1 organic manure, 24 kg P ha^-1 and 80 kg K ha^-1 and sprayed with Fe, Mn, Zn and Cu; sown on 15/4/2014, harvested on 13/7/2014 (95 days). Application of N was of positive response under all conditions and enhanced in presence of bio fertilizers. Application of bio fertilizers was of no or little effect end in some cases negative effect when given non combined with N. In presence of N all bio fertilizers increased yield and uptake of nutrients