Agronomic and physiological assessment of nitrogen use, uptake and acquisition in sunflower

A field experiment was conducted to study the effects of N fertilization on uptake,accumulation/remobilization, use efficiency and yield of sunflower grown in alluvial plains ofnorthwestern India comprising four hybrids (PSH 996, PAC 3789, PSH 569 and SH 3322)and five N levels (Control, 40, 80, 100 and 120 kg N ha-1) in split-plot design with threereplications. Increased N fertilizer rates significantly prompted sunflower yield only up to 100kg N ha-1. Every additional kilogram of N taken up increased sunflower yield by 26 kg ha-1.Significant genetic variation for seed yield and NUE traits explicated PSH 569 as the efficientone at sub-optimal N application while PSH 996 outperformed others at N80, N100 and N120. Drymatter accumulation pattern revealed average harvest index of 30% with 29% of the biomass asstalk, 19% as leaf and 22% as thalamus. Temporal changes in N acquisition indicated most ofthe total N uptake upto 50% flowering while maximum remobilization takes place duringreproductive phase. Significant correlation between N uptake and N use efficiency parameterswith yield indicate the importance of N nutrition in sunflower; LAI (r=0.841 **), N uptake(r=0.956**), NUpE (r= -0.814**), NUtE (r= -0.787**), NUE (r=-0.802**). Variation in NUE wasmore closely associated with NUpE (r=0.996**) than NUtE (r=0.812**) and linearly decreasedwith increasing leaf greenness (R2=0.70) and total leaf area (R2=0.81). This work willcomplement other studies to establish a baseline for breeding N efficient sunflower genotypesbe grown under semi-arid tropical conditions in India and similar environments.